MCAT gen chem chap 9 solutions 8%
coordinate covalent bond
" in which an electron pair donor (a Lewis base) and an electron pair acceptor (a Lewis acid) form very stable Lewis acid-base adducts." ex: hemoglobin
remember this about dissolutions
"Most dissolutions are endothermic, although the dissolution of gas into liquid is exothermic"
mcat expertise ksp
"On the MCAT, if you remember that Ksp is just a specialized form of Keq, then you can simplify a lot of problems by using the same concepts that you do for all equilibria, including Le Châtelier's principle."
"Describe the differences between solubility and saturation:" Excerpt From: Kaplan Test Prep. "MCAT General Chemistry Review 2021-2022." Apple Books.
"Solubility is the amount of solute contained in a solvent. Saturation refers to the maximum solubility of a compound at a given temperature; one cannot dissolve any more of the solute just by adding more at this temperature." Excerpt From: Kaplan Test Prep. "MCAT General Chemistry Review 2021-2022." Apple Books.
solubilty
"Solubility is the maximum amount of a solute that can be dissolved in a given solvent at a given temperature; it is often expressed as molar solubility—the molarity of the solute at saturation."
"What is one way in which solubility of a compound can be increased?
"Solubility of solids can be increased by increasing temperature. Solubility of gases can be increased by decreasing temperature or increasing the partial pressure of the gas above the solvent (Henry's law)" Excerpt From: Kaplan Test Prep. "MCAT General Chemistry Review 2021-2022." Apple Books.
"Describe the process of solvatio" Excerpt From: Kaplan Test Prep. "MCAT General Chemistry Review 2021-2022." Apple Books.
"Solvation refers to the breaking of intermolecular forces between solute particles and between solvent particles, with formation of intermolecular forces between solute and solvent particles. In an aqueous solution, water is the solvent." Excerpt From: Kaplan Test Prep. "MCAT General Chemistry Review 2021-2022." Apple Books.
"What is the molar solubility of Zn(OH)2 (Ksp = 4.1 × 10−17) in a 0.1 M solution of NaOH?" Excerpt From: Kaplan Test Prep. "MCAT General Chemistry Review 2021-2022." Apple Books.
"Start by writing the balanced reaction for the least soluble salt in the problem: Zn(OH)2 → Zn2+ + 2 OH- . Next, write out the Ksp equation and enter the variables for the concentrations. The Zn2+ concentration will equal x, the molar solubility under these conditions, but the OH- concentration will come from two contributors: the dissociated Zn(OH)2, and the 0.1 M NaOH solution. This results in the following Ksp expression: Ksp = [Zn2+][OH−]2 = (x)(0.1 + 2x)2. Since the Ksp for Zn(OH)2 is 4.1 x 10-17, x will be negligible compared to the 0.1 M from NaOH. The Ksp expression simplifies to: Ksp = (x)(0.1)2. Thus, 4.1 × 10−17 = 0.01x. x = molar solubility of Zn(OH)2= 4.1 × 10−15." Excerpt From: Kaplan Test Prep. "MCAT General Chemistry Review 2021-2022." Apple Books.
saturation point
"Systems move spontaneously toward the equilibrium position, and any movement away from equilibrium is nonspontaneous. In the process of creating a solution, the equilibrium is defined as the saturation point, where the solute concentration is at its maximum value for the given temperature and pressure. "
parts per million
"Though not a unique means of measuring concentration or dilution, the term "parts-per" can be used to indicate concentration of a dissolved substance in a solution (most commonly water). Parts-per-million (ppm, 10-6) is the most common usage. If a problem states there is one ppm of substance X in water, that would indicate there is 1 mg/L of water, as there would be 1 millionth of a gram per gram of water, and the density of water is 1 g/mL. On Test Day, prior to converting from ppm, make sure to assess whether conversion to a different unit of measure is actually required, as this conversion can typically be avoided on the MCAT." Excerpt From: Kaplan Test Prep. "MCAT General Chemistry Review 2021-2022." Apple Books.
"Determine the new boiling point of a solution containing 190 g MgCl2 in 1500 g water at room temperature: " Kb= .512 Excerpt From: Kaplan Test Prep. "MCAT General Chemistry Review 2021-2022." Apple Books.
190/95= 2 1500= 1.5 kg 2/1.5 *3 *.512= 2 k 373+2= 375 k
"An aqueous solution was prepared by mixing 70 g of an unknown nondissociating solute into 100 g of water. The solution has a boiling point of 101.0°C. What is the molar mass of the solute? (Note: kb= .512 ) 358 32 123 233 " Excerpt From: Kaplan Test Prep. "MCAT General Chemistry Review 2021-2022." Apple Books.
A "The equation ΔTb = iKbm can be used to solve this problem. The change in boiling point is 101.0 − 100 = 1.0°C. Then, plug that into: 1 k/ (1)(.512)= 2m The van't Hoff factor for this solute is 1 because the molecule does not dissociate into smaller components. Then, convert to grams of solute using the definition of molality: (2m)(.1kg)= .2 mol " "The mass used in this equation is 0.1 kg because 100 mL of water has a mass of 0.1 kg. Then, determine the molar mass: 70/.2= 350 which is closest to (A)." Excerpt From: Kaplan Test Prep. "MCAT General Chemistry Review 2021-2022." Apple Books. Excerpt From: Kaplan Test Prep. "MCAT General Chemistry Review 2021-2022." Apple Books.
"Lead is a toxic element that can cause many symptoms, including mental retardation in children. If a body of water is polluted with lead ions at 200 ppb (parts per billion), what is the concentration of lead expressed as molarity? (Note: The density of water is and ppb = grams per 109 grams of solution) 9.7 × 10−10 M Pb2+ 9.7 × 10−7 M Pb2+ 6.2 × 10−7 M Pb2+ 6.2 × 10−6 M Pb2+" Excerpt From: Kaplan Test Prep. "MCAT General Chemistry Review 2021-2022." Apple Books.
A B "200 ppb of Pb2+ is equivalent to 200 grams of Pb2+ in 109 grams of solution; given the extremely low concentration of lead, the mass of the water can be assumed to be approximately 109 grams, as well. To solve, set up a dimensional analysis question. The units needed at the end are moles per liter (molarity), so convert from grams of lead to moles of lead and grams of water to liters of water:" 200g pb/ 10e9 h20 1000g h20/ 1 l 1 mol pb/ 207 g 200e3/200e9 1e-6= 10e-7
"Two organic liquids, pictured in the figure below, are combined to form a solution. Based on their structures, will the solution closely obey Raoult's law? Yes; the liquids differ due to the additional methyl group on toluene and, therefore, will not deviate from Raoult's law. Yes; the liquids are very similar and, therefore, will not deviate from Raoult's law. No; the liquids differ due to the additional methyl group on toluene and, therefore, will deviate from Raoult's law. No; the liquids both contain benzene rings, which will interact with each other and cause deviation from Raoult's law." Excerpt From: Kaplan Test Prep. "MCAT General Chemistry Review 2021-2022." Apple Books.
B "Benzene and toluene are both organic liquids and have very similar properties. They are both nonpolar and are almost exactly the same size. Raoult's law states that ideal solution behavior is observed when solute-solute, solvent-solvent, and solute-solvent interactions are all very similar. Therefore, benzene and toluene in solution will be predicted to behave as a nearly ideal solution." Excerpt From: Kaplan Test Prep. "MCAT General Chemistry Review 2021-2022." Apple Books.
dilution
M1V1=M2V2 "M is molarity, V is volume, and the subscripts i and f refer to the initial and final values, respectively."
ideal solution
a solution that obeys Raoult's law -old and new interactions same energy, enthalpy is 0
solutions
homogeneous mixtures - "MCAT will focus almost exclusively on solids dissolved into aqueous solutions, but it's important to remember that solutions can be formed from different combinations of the three phases of matter."
colligative properties
properties that depend on the concentration of solute particles but not on their identity "vapor pressure depression, boiling point elevation, freezing point depression, and osmotic pressure—are usually associated with dilute solutions."
aqueous solution
solvent is water -rely on interactions between water and solutes - " It is also important to note that in some solutions, such as acids, the formation of a complex called the hydronium ion (H3O+) can occur. This is facilitated by the transfer of a hydrogen ion (H+) from a molecule in solution to a water molecule (H2O)." "CH3COOH (aq) + H2O (l) ⇌ CH3COO− (aq) + H3O+ (aq)" - h+ never found alone, always bound to a carrier- coordinate covalent bond
solutes
substance dissolved in a solution
freezing point depression
ΔTf = iKfm "where ΔTf is the freezing point depression, i is the van't Hoff factor, Kf is the proportionality constant characteristic of a particular solvent, and m is the molality of the solution. " The presence of solute particles in a solution interferes with the formation of the lattice arrangement of solvent molecules associated with the solid state. Thus, a greater amount of energy must be removed from the solution (resulting in a lower temperature) in order for the solution to solidify. For example, pure water freezes at 0°C, but for every mole of solute dissolved in 1 kg of water, the freezing point is lowered by 1.86°C. Therefore, the Kf for water is 1.86 As is the case for Kb, the values for Kf are unique to each solvent and will be provided on Test Day. "
van't Hoff factor
" corresponds to the number of particles into which a compound dissociates in solution. For example, i = 2 for NaCl because each formula unit of sodium chloride dissociates into two particles—a sodium ion and a chloride ion—when it dissolves. Covalent molecules such as glucose do not readily dissociate in water and thus have i values of 1." Excerpt From: Kaplan Test Prep. "MCAT General Chemistry Review 2021-2022." Apple Books.
another way to imagine entropy
" measure of molecular disorder, or the number of energy microstates available to a system at a given temperature" ex:nacl breaks up and has more components with interactions, thus increasing entropy absolutely - water decreses it's entropy because it has to be join to na or cl ions - over all entropy change is positive "Because of the relatively low endothermicity and relatively large positive change in entropy, sodium chloride will spontaneously dissolve in liquid water (ΔG = ΔH - TΔS)."
dilute and concentrated
"A solution in which the proportion of solute to solvent is small is said to be dilute, and one in which the proportion is large is said to be concentrated" -still considered unsaturated if max equillibrium is not reached
7 guidelines for aqeos solutions
"All salts containing ammonium (NH4+) and alkali metal (Group 1) cations are water-soluble. All salts containing nitrate (NO3−) and acetate (CH3COO−) anions are water-soluble. Halides (Cl−, Br−, I−), excluding fluorides, are water-soluble, with the exceptions of those formed with Ag+, Pb2+, and Hg22+. All salts of the sulfate ion (SO42−) are water-soluble, with the exceptions of those formed with Ca2+, Sr2+, Ba2+, and Pb2+. All metal oxides are insoluble, with the exception of those formed with the alkali metals, ammonium, and CaO, SrO, and BaO, all of which hydrolyze to form solutions of the corresponding metal hydroxides. All hydroxides are insoluble, with the exception of those formed with the alkali metals, ammonium, and Ca2+, Sr2+, and Ba2+. All carbonates (CO32−), phosphates (PO43−), sulfides (S2-), and sulfites (SO32−) are insoluble, with the exception of those formed with the alkali metals and ammonium."
"An ionic solid introduced into a polar solvent dissociates into its component ions, and the dissociation of such a solute in solution may be represented by"
"AmBn (s) ⇌ m An+ (aq) + n Bm− (aq)" balance first
MCAT expertise boiling and freezing
"As with boiling point elevation, there is a distinction between the calculated value and a final answer. The freezing point depression calculates the amount that the normal freezing point is lowered. As always, read the question to determine if it is asking for the change in temperature (ΔT) or the new (altered) boiling or freezing point." Excerpt From: Kaplan Test Prep. "MCAT General Chemistry Review 2021-2022." Apple Books.
bends
"Because gases become more soluble in solution as pressure increases, a diver who has spent time at significant depths under water will have more nitrogen gas dissolved in his or her blood because nitrogen gas is the main inert gas in the air we breathe. If the diver rises to the surface too quickly, the abrupt decompression will lead to an abrupt decrease in gas solubility in the plasma, resulting in the formation of nitrogen gas bubbles in the bloodstream. The gas bubbles can get lodged in the small vasculature of the peripheral tissue, mostly around the large joints of the body, causing pain and tissue damage (hence the name, the bends). The condition is painful and dangerous and can be fatal if not properly treated." Excerpt From: Kaplan Test Prep. "MCAT General Chemistry Review 2021-2022." Apple Books.
mcat expertise solubility
"Because most solutions in the real world involve water as the solvent, it is not a surprise that solutions are common on the MCAT. These solubility rules are not bad to know, but memorizing them all may be a little excessive. It is never a bad thing to know facts, but being able to apply them is more important. Know rules 1 and 2 for sure, and be aware of some of the more common insoluble exceptions, like Pb2+ and Ag+."
"What is a colligative property?" Excerpt From: Kaplan Test Prep. "MCAT General Chemistry Review 2021-2022." Apple Books.
"Colligative properties are those that depend on the amount of solute present, but not the actual identity of the solute particles. Examples include vapor pressure depression, boiling point elevation, freezing point depression, and osmotic pressure." Excerpt From: Kaplan Test Prep. "MCAT General Chemistry Review 2021-2022." Apple Books.
key concepts
"Every sparingly soluble salt of general formula MX will have Ksp = x2, where x is the molar solubility (assuming no common ion effect)." "Every sparingly soluble salt of general formula MX2 will have Ksp = 4x3, where x is the molar solubility (assuming no common ion effect)." "Every sparingly soluble salt of general formula MX3 will have Ksp = 27x4, where x is the molar solubility (assuming no common ion effect)."
maddness examples "A 0.1 mol sample of CuS is added to 1.00 L of 1.00 M NH3. What is the final concentration of the complex ion, tetraamminecopper(II)?" Excerpt From: Kaplan Test Prep. "MCAT General Chemistry Review 2021-2022." Apple Books.
"First determine the amount of copper ion produced from copper sulfide (CuS) in solution. Comparison of the two equilibrium constants shows that the CuS dissociation has a Ksp of 8 × 10-37, indicating that this reaction is unlikely to proceed as the forward reaction is not favorable. However, if the formation of the complex ion occurs simultaneously, the large Kf of 1.1 × 1013 for this process will drive the dissociation of CuS forward as the Cu2+ ions are consumed in the second reaction due to Le Châtlier's principle. Note that, even without quantitative analysis, the large value of Kf is a sign that the formation of the product of the second reaction will be highly favorable. In fact, if these two reactions are simultaneous, the CuS will ultimately be completely consumed due to this effect. Thus, the amount of Cu2+ available to react is given by The reactions given show a 1:1 relationship between the Cu2+ available and the [Cu(NH3)4]2+ that is generated. In other words, almost all of the Cu2+ ions will be used up to form the complex. Therefore, the concentration of the [Cu(NH3)4]2+ complex ion is 0.1 M. " Excerpt From: Kaplan Test Prep. "MCAT General Chemistry Review 2021-2022." Apple Books.
ex vapor pressure "What is the vapor pressure at room temperature of a mixture containing 58 g butane (C4H10) and 172 g hexane (C6H14)? (Note: The vapor pressures of pure butane and pure hexane are 172 kPa and 17.6 kPa, respectively, at 25°C.)" Excerpt From: Kaplan Test Prep. "MCAT General Chemistry Review 2021-2022." Apple Books.
"First, determine the number of moles of each substance. 58 g butane represents 1 mole of butane. 172 g hexane represents 2 moles of hexane. Then, determine the mole fractions of each component of the mixture. xbutane= mole butane/total= 1/3 xhexane= mole hexane/total= 2/3 Then, calculate the vapor pressure of each component: P butane= xbutanepbutane= 1/3 (172)= 57 phexane= xhaexanephexane= 2/3(17.6)= 12 57+12=69 The total vapor pressure is the sum of the two vapor pressures. Thus, the total vapor pressure is 60 + 12 = 72 kPa (actual = 69.1 kPa)." Excerpt From: Kaplan Test Prep. "MCAT General Chemistry Review 2021-2022." Apple Books.
"Calculate the Ksp of Ni(OH)2 in water, given that its molar solubility is 5.2 × 10−6 M." Excerpt From: Kaplan Test Prep. "MCAT General Chemistry Review 2021-2022." Apple Books.
"First, write out the balanced equation: Ni(OH)2= Ni2+. 2OH- Next, identify that the molar solubility x represents the amount of Ni(OH)2 that dissociates, creating x of Ni2+ and 2x of OH-. Write out the Ksp equation, and plug in the values of x to solve for Ksp: Ksp= (ni2+)(2OH-)= (x)(2x)^2 Ksp= (5.2e-6)(2*5.2e-6)^2 ksp= 5e-6 *(10 x 10e-6)^2= 5e-6 (10e-5) ksp= 5e-6 (10 e-10)= 5e-16 " Excerpt From: Kaplan Test Prep. "MCAT General Chemistry Review 2021-2022." Apple Books.
example of common ion
"For example, if a salt such as CaF2 is dissolved into water already containing Ca2+ ions (from some other salt, perhaps CaCl2), the solution will dissolve less CaF2 than would an equal amount of pure water. The common ion effect is really Le Châtelier's principle in action. Because the solution already contains one of the constituent ions from the products side of the dissociation equilibrium, the system will shift toward the left side, reforming the solid salt. As a result, molar solubility for the solid is reduced, and less of the solid dissolves in the solution—although the Ksp remains constant." Excerpt From: Kaplan Test Prep. "MCAT General Chemistry Review 2021-2022." Apple Books.
complex ions
"Formation of complex ions increases the solubility of otherwise insoluble ions (the opposite of the common ion effect)." "The process of forming a complex ion involves electron pair donors and electron pair acceptors such as those seen in coordinate covalent bonding."
Name two ions that form salts that are always soluble:" Excerpt From: Kaplan Test Prep. "MCAT General Chemistry Review 2021-2022." Apple Books.
"Group I metals, ammonium, nitrate, and acetate salts are always soluble" Excerpt From: Kaplan Test Prep. "MCAT General Chemistry Review 2021-2022." Apple Books.
key concept ip
"IP < Ksp: unsaturated, solute will continue to dissolve IP = Ksp: saturated, solution is at equilibrium IP > Ksp: supersaturated, precipitation will occur"
solubility product constant (Ksp)
"Ksp = [An+]m[Bm-]n " " For example, we can express the Ksp of silver chloride as: "AgCl (s) ⇌ Ag+ (aq) + Cl− (aq)" Ksp = [Ag+][Cl−]" "You'll notice that, for the law of mass action of solutions, there is no denominator. Remember that pure solids and liquids do not appear in the equilibrium constant. Because the silver chloride solution was formed by adding pure solid silver chloride to pure water, neither the solid silver chloride nor the water is included. Indeed, dissociation reactions—by definition—have a solid salt as a reactant; thus, Ksp expressions should never have denominators." - temperature dependent -pressure dependent if gas in liquid - " the solubility product constant increases with increasing temperature for non-gas solutes and decreases for gas solutes. Higher pressures favor dissolution of gas solutes, and therefore the Ksp will be larger for gases at higher pressures than at lower ones. "
"How are molality and molarity related for water? How are they related for other solvents?" Excerpt From: Kaplan Test Prep. "MCAT General Chemistry Review 2021-2022." Apple Books.
"Molarity (M) and molality (m) are nearly equal at room temperature. This is only because 1 L solution is approximately equal to 1 kg solvent for dilute solutions (the denominators of the molarity and molality equations, respectively). For other solvents, molarity and molality differ significantly because their densities are not 1 g/ml like water." Excerpt From: Kaplan Test Prep. "MCAT General Chemistry Review 2021-2022." Apple Books.
MCAT expertise molarity
"Note that for dilute solutions, the volume of the solution is approximately equal to the volume of solvent used, which simplifies our calculations on Test Day. However, technical questions could ask you to distinguish between these two. For example, when you add two kilograms of sucrose (table sugar) to a liter of water at room temperature (achieving saturation), the volume of solution is certainly larger than 1 L!" REMEBER ITS LITERS
osmotic pressure
"Osmotic pressure refers to a "sucking" pressure generated by solutions in which water is drawn into a solution. Formally, the osmotic pressure is the amount of pressure that must be applied to counteract this attraction of water molecules for the solution. The equation for osmotic pressure is: ∏ = iMRT" "where ∏ is the osmotic pressure, i is the van't Hoff factor, M is the molarity of the solution, R is the ideal gas constant, and T is the temperature." water moves in direction of higher solute concentration
mca xpertise normality
"Simple ideas on Test Day will make things easier. So, when you come across normality, think of it as molarity of the stuff of interest in the reaction." Excerpt From: Kaplan Test Prep. "MCAT General Chemistry Review 2021-2022." Apple Books.
key to remembe r
"Sodium and nitrate ions are generally used as counterions to what is actually chemically important; for example, if a pH problem gives a sodium formate concentration of 0.10 M, it is really indicating that the concentration of the formate ion is 0.10 M because the sodium ion concentration does not affect pH. The only time one needs to worry about the nitrate ion concentration is in an oxidation-reduction reaction, for the nitrate ion can function—although only weakly—as an oxidizing agent. In all other cases with nitrate ions, only focus on the cation as the chemically reacting species."
"The Ksp of Ba(OH)2 is 5.0 × 10−3. Assuming that barium hydroxide is the only salt added to form a solution, calculate the ion product of the following solutions based on the concentration of Ba2+. Then, predict the behavior of the given solutions (dissolution, equilibrium, or precipitation): [Ba2+] Ion Product Behavior of Solution 0.5 M 0.1 M 0.05 M " Excerpt From: Kaplan Test Prep. "MCAT General Chemistry Review 2021-2022." Apple Books.
"Start with the balanced reaction and calculation for Ksp, which can also be used to calculate Q. Keep in mind that for every x of Ba(OH)2 that dissolves, x of Ba2+ will be produced, and 2x of OH-." Ba(OH)2= Ba2+ 2OH- kap= (Ba2+)(OH-)^2 "[Ba2+] Ion Product Behavior of Solution 0.5 M (0.5 M)(1 M)2 = 0.5 0.5 > 5.0 × 10−3 → precipitation 0.1 M (0.1 M)(0.2 M)2 = 4.0 × 10−3 4.0 × 10−3 < 5.0 × 10−3 → dissolution 0.05 M (0.05 M)(0.1 M)2 = 5.0 × 10−4 5.0 × 10−4 < 5.0 × 10−3 → dissolution" "Note that the concentration of hydroxide is double that of barium. While there will be a very small contribution of hydroxide from the autoionization of water, this amount is negligible compared to the values given in the question."
MCAT expertise boiling point wlwvation
"The boiling point elevation formula calculates the amount that the normal boiling point is raised. The value calculated is not the boiling point itself." Excerpt From: Kaplan Test Prep. "MCAT General Chemistry Review 2021-2022." Apple Books.
common ion ex "The Ksp of AgI in aqueous solution is 8.5 × 10−17. If a 1 × 10−5 M solution of AgNO3 is saturated with AgI, what will be the final concentration of the iodide ion?"
"The concentration of Ag+ in the original AgNO3 solution will be 1 × 10−5 M because AgNO3 will fully dissociate (review the solubility rules from earlier in this chapter). Some small amount of AgI will dissociate into the solution, which is the molar solubility x of AgI under these conditions. The net silver concentration from both AgNO3 and AgI will become 1 × 10−5 M + x. Because no iodide was present in solution until the AgI began dissociating, the concentration of iodide will be x. Thus, the Ksp expression for the dissociation of AgI can be written as:" Ksp= (Ag)(I) 8.5e-17= (1e=5 + x)(x) "Given that the value of Ksp for this reaction is 10-16, only a minuscule amount of AgI will be dissociated. Thus, the value of x is sufficiently small to be negligible when added to 10-5. Thus, the math simplifies to:" 8.5e-17 = (1e-5)X 8.5e-12=x "This question asks for the concentration of iodide, which—based on the equilibrium expression—is represented by x. Thus, [I−] = 8.5× 10−12 M."
ex more maddness "What are the concentrations of each of the ions in a saturated solution of CuBr, given that the Ksp of CuBr is 6.27 × 10−9 at 25°C? If 3 g CuBr are dissolved in water to make 1 L of solution at 25°C, would the solution be saturated, unsaturated, or supersaturated?"
"The first step is to write out the dissociation reaction: CuBr (s) → Cu+ (aq) + Br− (aq) Ksp = [Cu+][Br−] Let x equal the molar solubility of CuBr, which is the amount of CuBr that dissolves at equilibrium. The concentration of Cu+ and Br- will each equal x. " ksp= x*x= x^2 6.27e-9= x^2 6.3e-9=x^2 63e-10=x^2 8e-5=x "Therefore, [Cu+] is about 8 × 10-5 M, and [Br−] is also about 8 × 10−5 M. Note that 8 × 10−5 M also represents the molar solubility of copper(I) bromide. Next, we convert 3 g of CuBr into moles: 3/150= .002 2 × 10−2 mol CuBr in 1 L of solution represents a molarity of 2 × 10−2 M, which is more than 100 times higher than the molar solubility of CuBr. Therefore, this is a supersaturated solution."
complex and common ions
"The formation or stability constant (Kf) is the equilibrium constant for complex formation. Its value is usually much greater than Ksp. The formation of a complex increases the solubility of other salts containing the same ions because it uses up the products of those dissolution reactions, shifting the equilibrium to the right (the opposite of the common ion effect). The common ion effect decreases the solubility of a compound in a solution that already contains one of the ions in the compound. The presence of that ion in solution shifts the dissolution reaction to the left, decreasing its dissociation." Excerpt From: Kaplan Test Prep. "MCAT General Chemistry Review 2021-2022." Apple Books.
ex of this bogusness "The molar solubility of Fe(OH)3 in an aqueous solution was determined to be 4 x10^-10 What is the value of the Ksp for Fe(OH)3 at the same temperature and pressure?" Excerpt From: Kaplan Test Prep. "MCAT General Chemistry Review 2021-2022." Apple Books.
"The molar solubility is given as 4 × 10−10 M. The equilibrium concentration of each ion can be determined from the molar solubility and the balanced dissociation reaction of Fe(OH)3. The dissociation reaction is: Fe(OH)3 (s) ⇌ Fe3+ (aq) + 3 OH− (aq) Ksp = [Fe3+][OH−]3 The molar solubility can be expressed as x, the amount of Fe(OH)3 that dissolves to make a saturated solution at equilibrium. As it dissolves, Fe(OH)3 dissociates to create x of Fe2+ and 3x of OH-. This can be entered into the Ksp equation to give: Ksp = [x][3x]3 If the molar solubility x is 4 × 10−10 M, then x = 4 × 10−10 M Fe(OH)3 has dissolved, yielding x = 4 × 10−10 M Fe3+ and 3x = 3 × 4 × 10−10 M OH− (because there are three OH− ions released per Fe(OH)3 molecule dissolved). Thus, " (4e-10)(3x4e-10)^3 (4e-10)(27x4e-10)^3 27x4e-10^4 27s256e-40 =7500e-40= 7,5e-37
ex freezing point depression "400 g of AlCl3 is dissolved in 1.5 L of water at room temperature Kf- 1.86. What is the new freezing point of this solution?" Excerpt From: Kaplan Test Prep. "MCAT General Chemistry Review 2021-2022." Apple Books.
"Using the same variables for i and m from the previous example, (4)(1.86)(2m)= 15 The normal freezing point of water is 273 K. The freezing point is going to be depressed (or decreased) by 15 K. The new freezing point is therefore 273 - 15 = 258 K = -15°C." Excerpt From: Kaplan Test Prep. "MCAT General Chemistry Review 2021-2022." Apple Books.
key oncept vapor pressure depression
"Vapor pressure depression goes hand in hand with boiling point elevation. The lowering of a solution's vapor pressure would mean that a higher temperature is required to match atmospheric pressure, thereby raising the boiling point."
ex boiling point elevation "400 g AlCl3 is dissolved in 1.5 L of water at room temperature K= .512. How much does the boiling point increase after adding the aluminum chloride?" Excerpt From: Kaplan Test Prep. "MCAT General Chemistry Review 2021-2022." Apple Books.
"Water at room temperature has a density of 1 g/l Therefore, 1.5 L is the same as 1.5 kg. The van't Hoff factor for aluminum chloride is 4 because it breaks down to form 1 aluminum cation and 3 chloride anions. To determine the molality, we will also need to know how many moles 400 g AlCl3 represents. 400/133.5- 3 mol. The molality is therefore 3/1.5- 2 m Then, plug into the boiling point elevation equation. (4)(.512)(2)= 4 k " Excerpt From: Kaplan Test Prep. "MCAT General Chemistry Review 2021-2022." Apple Books.
relationship between vapor pressure deprssion and boiling point elevation
"We've just seen that adding solute to a solvent results in a decrease in the vapor pressure of the solvent in the solution. If the vapor pressure of a solution is lower than that of the pure solvent, then more energy (and consequently a higher temperature) will be required before its vapor pressure equals the ambient pressure." Excerpt From: Kaplan Test Prep. "MCAT General Chemistry Review 2021-2022." Apple Books.
ex of dissoltion with enthalpy and entropy
"When NaCl dissolves in water, its component ions dissociate from each other and become surrounded by water molecules. For this new interaction to occur, ionic bonds between Na+ and Cl− must be broken, and hydrogen bonds between water molecules must also be broken. This step requires energy and is therefore endothermic. Because water is polar, it can interact with each of the component ions through ion-dipole interactions: the partially positive hydrogen end of the water molecules will surround the Cl− ions, and the partially negative oxygen end of the water molecules will surround the Na+ ions, as shown in Figure 9.2. The formation of these ion-dipole bonds is exothermic, but the magnitude is slightly less than the energy required to break the ionic bonds and hydrogen bonds. As a result, the overall dissolution of table salt into water is endothermic and favored at high temperatures. "
gibbs and solubility
"When the change in Gibbs free energy for the dissolution reaction is negative at a given temperature, the process will be spontaneous, and the solute is said to be soluble. When the change in Gibbs free energy is positive, the process will be nonspontaneous, and the solute is said to be insoluble"
ex solubility with glucose
"at 25°C, a maximum of 90.9 g glucose will dissolve in 100 mL H2O. Thus, the solubility of glucose is 909 g/L If more glucose is added to an already saturated glucose solution, it will not dissolve but rather will remain in solid form, precipitating to the bottom of the container."
formation of complex ions
"increases the solubility of a salt in solution" very high Ksp values ex FE and CN. forms FeCN6 3- "When forming a complex ion, one must often use a mixture of solutions. For this reason, a distinction must be made between the Ksp of the solution and that of the complex ion itself. The dissolution of the original solution is termed Ksp, and the subsequent formation of the complex ion in solution is termed Kf (the formation or stability constant of the complex in solution). An example is shown below in which the diamminesilver(I) complex is formed in a silver chloride solution:" "Notice that the formation constant (Kf) of the complex ion is significantly larger than the Ksp of the compound providing the metal ion. This is part of the explanation for why the initial dissolution of the metal ion is the rate-limiting step of complex ion formation. However, Le Châtelier's principle is at play in these reactions as well. Ultimately, complex ions form to become more soluble in solution. And as an amount of silver ion is being used up to form the complex ion itself, the dissociation reaction of AgCl shifts to the right, providing more silver for complex ion formation." Excerpt From: Kaplan Test Prep. "MCAT General Chemistry Review 2021-2022." Apple Books.
solutes considered soluble if
"molar solubility above 0.1 M in solution. " Excerpt From: Kaplan Test Prep. "MCAT General Chemistry Review 2021-2022." Apple Books.
solubility
"of a substance is the maximum amount of that substance that can be dissolved in a particular solvent at a given temperature. When this maximum amount of solute has been added, the dissolved solute is in equilibrium with its undissolved state, and we say that the solution is saturated."
ion product
"which is analogous to the reaction quotient, Q, for other chemical reactions. The ion product equation has the same form as the equation for the solubility product constant: IP = [An+]m[Bm-]n" - compare to ksp, basically Q - if IP < Ksp, unsaturated solution. "dissolution is thermodynamically favored over precipitation" - IP>Ksp, supersaturated, can precipitate if disturbed IP=Ksp, saturated, precipitate and dissolution equal. - molarilty of saturated solution called molar solubility
exothermic solvation
- new interactions stronger than original -favored at low temp - "Le Châtelier's principle tells us this is the reason that lowering the temperature of a liquid favors solubility of a gas in the liquid."
"Determine the freezing point depression of a solution containing 58.5 g of NaCl in 1800 g of water at room temperature:"Kf= 1.86 Excerpt From: Kaplan Test Prep. "MCAT General Chemistry Review 2021-2022." Apple Books.
1/1.8 *1.86 * 2 = 2 k= 271 k
molality ex: "If 10 g NaOH are dissolved in 500 g of water, what is the molality of the solution" Excerpt From: Kaplan Test Prep. "MCAT General Chemistry Review 2021-2022." Apple Books.
10/40= mol naoh .25/.5kg = .5m
"Determine the vapor pressure of a solution containing 190 g MgCl2 in 540 g water at room temperature: (Note: The vapor pressure of pure water at 25°C is 3.2 kPa.)" Excerpt From: Kaplan Test Prep. "MCAT General Chemistry Review 2021-2022." Apple Books.
190/95= 2 mol 540/18= 30 mol 30/32 (3.2)= 3 kPa
"Which of the following combinations of liquids would be expected to have a vapor pressure higher than the vapor pressure that would be predicted by Raoult's law? Ethanol and hexane Acetone and water Isopropanol and methanol Nitric acid and water" Excerpt From: Kaplan Test Prep. "MCAT General Chemistry Review 2021-2022." Apple Books.
A "Mixtures that have a higher vapor pressure than predicted by Raoult's law have stronger solvent-solvent and solute-solute interactions than solvent-solute interactions. Therefore, particles do not want to stay in solution and more readily evaporate, creating a higher vapor pressure than an ideal solution. Two liquids that have different properties, like hexane (hydrophobic) and ethanol (hydrophilic, small) in (A), would not have many interactions with each other and would cause positive deviation; i.e. higher vapor pressure. (B) and (C) are composed of liquids that are similar to one another and would not show significant deviation from Raoult's law. (D) contains two liquids that would interact very well with each other, which would actually cause a negative deviation from Raoult's law—when attracted to one other, solutes and solvents prefer to stay in liquid form and have a lower vapor pressure than predicted by Raoult's law." Excerpt From: Kaplan Test Prep. "MCAT General Chemistry Review 2021-2022." Apple Books.
mixtures
A combination of two or more substances that are not chemically combined "all solutions are considered mixtures, but not all mixtures are considered solutions."
solvent
A liquid substance capable of dissolving other substances " If the two substances are already in the same phase (for example, a solution of two liquids), the solvent is the component present in greater quantity. If the two same-phase components are in equal proportions in the solution, then the component that is more commonly used as a solvent in other contexts is considered the solvent."
"When ammonia, NH3, is used as a solvent, it can form complex ions. For example, dissolving AgCl in NH3 will result in the complex ion [Ag(NH3)]2+. What effect would the formation of complex ions have on the solubility of a compound like AgCl in NH3? The solubility of AgCl will increase because complex ion formation will cause more ions to exist in solution, which interact with AgCl to cause it to dissociate. The solubility of AgCl will increase because complex ion formation will consume Ag+ ions and cause the equilibrium to shift away from solid AgCl. The solubility of AgCl will decrease because Ag+ ions are in complexes, and the Ag+ ions that are not complexed will associate with Cl− to form solid AgCl. The solubility of AgCl will decrease because complex ion formation will consume Ag+ ions and cause the equilibrium to shift toward the solid AgCl." Excerpt From: Kaplan Test Prep. "MCAT General Chemistry Review 2021-2022." Apple Books.
B "Formation of complex ions between silver ions and ammonia will cause more molecules of solid AgCl to dissociate. The equilibrium is driven toward dissociation because the Ag+ ions are essentially being removed from solution when they complex with ammonia. This rationale is based upon Le Châtelier's principle, stating that when a chemical equilibrium experiences a change in concentration, the system will shift to counteract that change." Excerpt From: Kaplan Test Prep. "MCAT General Chemistry Review 2021-2022." Apple Books.
"Reverse osmosis is a process that allows fresh water to be obtained by using pressure to force an impure water source through a semi-permeable membrane that only allows water molecules to pass. What is the minimum pressure that would be required to purify seawater at 25°C that has a total osmolarity of 1,000 mOsm/L? 23.5 atm 24.5 atm 24,000 atm 24,500 atm" Excerpt From: Kaplan Test Prep. "MCAT General Chemistry Review 2021-2022." Apple Books.
B "Osmotic pressure is given by the formula pi= iMRT Entering the values from the question stem gives: (1000 e-3)(.08)(298 k) 1 x .08 x 300= 24 Notice that the concentration of seawater is given for all solutes, which represents i×M. It is also given in mOsm/L, which is converted to moles per liter by multiplying by 10-3. Also, the question asks for the minimum pressure required, which means that the correct answer choice must be slightly above the calculated pressure in order for reverse osmosis to proceed."
"Which of the following will cause the greatest increase in the boiling point of water when it is dissolved in 1.00 kg H2O? 0.4 mol calcium sulfate 0.5 mol iron(III) nitrate 1.0 mol acetic acid 1.0 mol sucrose" Excerpt From: Kaplan Test Prep. "MCAT General Chemistry Review 2021-2022." Apple Books.
B "The equation to determine the change in boiling point of a solution is as follows: ΔTb = iKbm. m is the molality of the solution, and Kb is the boiling point elevation constant. In this case, the solvent is always water, so Kb will be the same for each solution. What is needed is the number of dissociated particles from each of the original species. This is referred to as the van't Hoff factor (i) and is multiplied by molality to give a normality (the concentration of the species of interest—in this case, all particles). The normality values determine which species causes the greatest change in boiling point. Species Number of Moles Number of Dissolved Particles i × m (Normality) CaSO4 0.4 2 0.8 Fe(NO3)3 0.5 4 2.0 CH3COOH 1.0 Between 1 and 2 (acetic acid is a weak acid and a low percentage of the molecules will dissociate into 2 particles) Between 1.0 and 2.0" "C12H22O11 1.0 1 1.0 The choice is between iron(III) nitrate and acetic acid. The fact that acetic acid is a weak acid indicates that only a few particles will dissociate into H+ and acetate. Therefore, the normality of the acetic acid will be much closer to 1.0 than 2.0." Excerpt From: Kaplan Test Prep. "MCAT General Chemistry Review 2021-2022." Apple Books.
"One hundred grams of sucrose are dissolved in a cup of hot water at 80°C. The cup of water contains 300.00 mL of water. What is the percent composition by mass of sugar in the resulting solution? (Note: Sucrose = C12H22O11, density of water at 80C= .975) 25.0% 25.5% 33.3% 34.2%" Excerpt From: Kaplan Test Prep. "MCAT General Chemistry Review 2021-2022." Apple Books.
B "The mass percent of a solute equals the mass of the solute divided by the mass of the total solution times 100%. Plug in the values given for sucrose, the volume of water and the density of water to determine the %mass of sucrose. Keep in mind that in rounding while calculating, the denominator was estimated to be larger than the actual value, thus giving an answer that is slightly lower than the actual value. Thus, the correct answer is (B), 25.5%. (A) results if rounding error is not taken into account. While these answers are very close, the mass of the water must be slightly less than 300 g, given the density value, so the percent composition of sucrose must be slightly higher than 25%. If the solute's mass is not added to the solvent's, the calculated value is 34.2%, which is (D). (C) neglects both the addition step and the rounding error." Excerpt From: Kaplan Test Prep. "MCAT General Chemistry Review 2021-2022." Apple Books.
"A saturated solution of cobalt(III) hydroxide (Ksp = 1.6 × 10−44) is added to a saturated solution of thallium(III) hydroxide (Ksp = 6.3 × 10−46). What is likely to occur? Both cobalt(III) hydroxide and thallium(III) hydroxide remain stable in solution. Cobalt(III) hydroxide precipitates and thallium(III) hydroxide remains stable in solution. Thallium(III) hydroxide precipitates and cobalt(III) hydroxide remains stable in solution. Both thallium(III) hydroxide and cobalt(III) hydroxide precipitate." Excerpt From: Kaplan Test Prep. "MCAT General Chemistry Review 2021-2022." Apple Books.
B C "Thallium (III) hydroxide has a lower Ksp value than cobalt (III) hydroxide. It is important to note that one can assume the molar solubility of thallium (III) hydroxide is lower than cobalt (III) hydroxide only because both salts have a formula MX3 (one of one particle, three of another). When the solutions are mixed, [OH-] is at saturation levels in the cobalt solution, which is higher than saturation levels in the thallium solution. Therefore the ion product for thallium (III) hydroxide is higher than its solubility product constant, and the system will shift left to form solid thallium (III) hydroxide, which precipitates." Excerpt From: Kaplan Test Prep. "MCAT General Chemistry Review 2021-2022." Apple Books.
"The entropy change when a solution forms can be expressed by the term ΔS°soln. When water molecules become ordered around an ion as it dissolves, the ordering would be expected to make a negative contribution to ΔS°soln. An ion that has more charge density will have a greater hydration effect, or ordering of water molecules. Based on this information, which of the following compounds will have the most negative contribution to ΔS°soln? KCl CsI CaS NaCl" Excerpt From: Kaplan Test Prep. "MCAT General Chemistry Review 2021-2022." Apple Books.
C "CaS will cause the most negative contribution to ΔS°soln through hydration effects because the Ca2+ and S2− ions have the highest charge density compared to the other ions. All of the other ions have charges of +1 or -1,whereas Ca2+ and S2− each have charges with a magnitude of 2." Excerpt From: Kaplan Test Prep. "MCAT General Chemistry Review 2021-2022." Apple Books.
"Which of the following explanations best describes the mechanism by which solute particles affect the melting point of ice? Melting point is elevated because the kinetic energy of the substance increases. Melting point is elevated because the kinetic energy of the substance decreases. Melting point is depressed because solute particles interfere with lattice formation. Melting point is depressed because solute particles enhance lattice formation." Excerpt From: Kaplan Test Prep. "MCAT General Chemistry Review 2021-2022." Apple Books.
C "Melting point depresses upon solute addition, making (A) and (B) incorrect. Solute particles interfere with lattice formation, the highly organized state in which solid molecules align themselves. Colder-than-normal conditions are necessary to create the solid structure." Excerpt From: Kaplan Test Prep. "MCAT General Chemistry Review 2021-2022." Apple Books.
"The salt KCl is dissolved in a beaker. To an observer holding the beaker, the solution begins to feel colder as the KCl dissolves. From this observation, one could conclude that: ΔS°soln is large enough to overcome the unfavorable ΔH°soln. KCl is mostly insoluble in water. ΔS°soln must be negative when KCl dissolves. boiling point depression will occur in this solution." Excerpt From: Kaplan Test Prep. "MCAT General Chemistry Review 2021-2022." Apple Books.
C A "Dissolution is governed by enthalpy and entropy, which are related by the equation ΔG°soln = ΔH°soln − TΔS°soln. The cooling of the solution indicates that heat is used up in this bond-breaking reaction. In other words, dissolution is endothermic, and ΔH is positive. The reaction is occurring spontaneously, so ΔG must be negative. The only way that a positive ΔH can result in a negative ΔG is if entropy, ΔS, is a large, positive value as in (A). Conceptually, that means that the only way the solid can dissolve is if the increase in entropy is great enough to overcome the increase in enthalpy. (B) is incorrect because it is clearly stated in the question stem that KCl dissolves; further, all salts of Group 1 metals are soluble. (C) is incorrect because ΔS°soln must be positive in order for KCl to dissolve. Finally, (D) is incorrect because solute dissolution would cause the boiling point to elevate, not depress. It is also not a piece of evidence that could be found simply by observing the beaker's temperature change" Excerpt From: Kaplan Test Prep. "MCAT General Chemistry Review 2021-2022." Apple Books.
"Which phases of solvent and solute can form a solution? Solid solvent, gaseous solute Solid solvent, solid solute Gaseous solvent, gaseous solute I and II only I and III only II and III only I, II, and III" Excerpt From: Kaplan Test Prep. "MCAT General Chemistry Review 2021-2022." Apple Books.
C D "All three choices can make a solution as long as the two components create a mixture that is of uniform appearance (homogeneous). Hydrogen in platinum is an example of a gas in a solid. Brass and steel are examples of homogeneous mixtures of solids. The air we breathe is an example of a homogeneous mixture of gases; while these are more commonly simply referred to as mixtures, they still fit the criteria of a solution." Excerpt From: Kaplan Test Prep. "MCAT General Chemistry Review 2021-2022." Apple Books.
"The following equilibrium exists when AgBr (Ksp = 5.35 × 10−13) is in solution: AgBr (s) ⇌ Ag+ (aq) + Br− (aq) What is the solubility (g/l) of AgBr in a solution of 0.0010 M NaBr? " Excerpt From: Kaplan Test Prep. "MCAT General Chemistry Review 2021-2022." Apple Books.
D "The solubility of AgBr can be determined using the Ksp value given in the equation. Some amount of AgBr will dissolve; this is the molar solubility x for these conditions. When AgBr dissociates, there will be x amount of silver(I) formed and x amount of bromide—which is added to the 0.0010 M Br- already present from NaBr. 5.35 e-13- (x)(.0010 M + x) Given the Ksp of 5.4 × 10-13, x will be negligible compared to 0.0010 M. Thus, the math can be simplified to: 5.35 e -13= (x)(.001) 5.35e-13/.10e-3 Therefore, x, the molar solubility, is 5.35 × 10−10, which looks like (C). However, the units of the answer choices are grams per liter, not molarity, and the result must be multiplied by the molar mass 187.8 5.35 x 187.8= 5e -10 x200= 1000e-10= 1 e -7 which is close to (D). Note that a very accurate approximation was reached by rounding down the first number and rounding up the second, balancing the error."
"The process of formation of a salt solution can be better understood by breaking the process into three steps: Breaking the solute into its individual components Making room for the solute in the solvent by overcoming intermolecular forces in the solvent Allowing solute-solvent interactions to occur to form the solution Which of the following correctly lists the enthalpy changes for these three steps, respectively? Endothermic, exothermic, endothermic Exothermic, endothermic, endothermic Exothermic, exothermic, endothermic Endothermic, endothermic, exothermic" Excerpt From: Kaplan Test Prep. "MCAT General Chemistry Review 2021-2022." Apple Books.
D "The first step will most likely be endothermic because energy is required to break molecules apart. The second step is also endothermic because the intermolecular forces in the solvent must be overcome to allow incorporation of solute particles. The third step will most likely be exothermic because polar water molecules will interact with the dissolved ions, creating a stable solution and releasing energy." Excerpt From: Kaplan Test Prep. "MCAT General Chemistry Review 2021-2022." Apple Books.
"You are working in a sewage treatment facility and are assaying chlorine in a water sample. You need to dilute the water sample from 100 ppm stock to 25 ppm and create 100 mL of solution. Calculate the amount of stock solution needed and determine how you would create your final solution:" Excerpt From: Kaplan Test Prep. "MCAT General Chemistry Review 2021-2022." Apple Books.
MiVi= MfVf= Vi=MfVf/Mi= 25*100/ 100 ml= 25 ml "Thus, start with 25 mL of the stock solution and add 75 mL pure water to get 100 mL of solution with 25 ppm Cl2." Excerpt From: Kaplan Test Prep. "MCAT General Chemistry Review 2021-2022." Apple Books.
molarity
Moles of solute/ liters of solution -most common form -indicated using brackets - denominator is solutio volume, not volume of solvent used to prepare solution - "Molarity is used for rate laws, the law of mass action, osmotic pressure, pH and pOH, and the Nernst equation."
Raoult's Law
PA = XAPA° "where PA is the vapor pressure of solvent A when solutes are present, XA is the mole fraction of the solvent A in the solution, and PA° is the vapor pressure of solvent A in its pure state." only ideal soltions accounts for vapor pressure depression caused by solutes in solution. As solute is added to a solvent, the vapor pressure of the solvent decreases proportionately. add solute to solution, increase temp needed to reached boiling point For example, consider compound A in Figure 9.9. Compound A in its pure form (mole fraction = 1.0) has a particular vapor pressure, indicated by PA° . At the same temperature, compound B has a lower vapor pressure, indicated by PB° . Note that, as the concentration of B increases, the vapor pressure of A decreases. Indeed, as more solute is dissolved into solvent (as more B is dissolved into A), the vapor pressure of the solvent decreases." "On a molecular level, the presence of the solute molecules can block the evaporation of solvent molecules but not their condensation. This reduces the vapor pressure of the solution compared to the pure solvent, as seen in Figure 9.10."
sparingly soluble salts
Solutes that dissolve minimally in the solvent, molar solubility under 0.1 M.
ex vapor depression "What is the change in vapor pressure when 180 grams of glyceraldehyde (C3H6O3) are added to 0.18 L of water at 100°C?
Solution: The density of water at 100°C is close to 1g/ml and the vapor pressure of water at the same temperature is 1 atm because this is the boiling point of water. In order to find the mole fraction of the solvent, first find the molar mass of the solute (glyceraldehyde) and solvent (water). 180 g glyceraldehyde represents 2 moles of glyceraldehyde. 0.18 L of water has a mass around 180 g, which represents 10 moles of water. The mole fraction of water is therefore 10 mol water/ 12 mole total= 5/6 = .833 To find the vapor pressure change, we want to find the difference in the old pressure and the new pressure. The new pressure can be calculated from Raoult's law: PA = XAPA° = (0.83)(1 atm) = 0.83 atm. The change in vapor pressure is therefore 1 atm - 0.83 atm = 0.17 atm."
chelation
The process of binding metal ions to the same ligand at multiple points ."Chelation therapy is often used to sequester toxic metals (lead, arsenic, mercury, and so on). Even biologically necessary metals, such as iron, can be toxic in overload states; "
solvation
The process of surrounding solute particles with solvent particles to form a solution -also known as dissolution -when solvent is what, termed hydration - "Solvation involves breaking intermolecular interactions between solute molecules and between solvent molecules and forming new intermolecular interactions between solute and solvent molecules together"
common ion effect
a decrease in the solubility of an ionic compound caused by the addition of a common ion "As described above, the molar solubility of a compound is its concentration (in moles per liter) at equilibrium at a given temperature. If X moles of AmBn (s) can be dissolved in one liter of solution to reach saturation, then the molar solubility of AmBn (s) is X molar." "Pay attention to the effect of the common ion: its presence results in a reduction in the molar solubility of the salt. "
coordination compound
compound composed of complex ion and counter ions sufficient to give no net charge "refers to a molecule in which a cation is bonded to at least one electron pair donor (which could include the water molecule). The electron pair donor molecules are called ligands"
dissolution takes place if
enthalpy and entropy - at constant temp and pressure, entropy always increases upon dissolution - "spontaneous processes are associated with a decrease in free energy, while nonspontaneous processes are associated with an increase in free energy. Thus, whether or not dissolution will happen spontaneously depends on both the change in enthalpy and the change in entropy for the solute and solvent of the system."
percent by mass
mass of solute/mass of solution x 100 -aq, solid solutions,
ex "What is the percent composition by mass of a salt water solution if 100 g of the solution contains 20 g of NaCl?" Excerpt From: Kaplan Test Prep. "MCAT General Chemistry Review 2021-2022." Apple Books.
mass solute/ mass sol x100 20/100 *100= 20%
diluton ex "A chemist wishes to prepare 300 mL of a 1.1 M NaOH solution from a 5.5 M NaOH stock solution. What volume of stock solution should be diluted with pure water to obtain the desired solution?" Excerpt From: Kaplan Test Prep. "MCAT General Chemistry Review 2021-2022." Apple Books.
mivi=mfvf 1.1*300/5.5=60 safe to keep ml
"A stock solution for making typical IV saline bags contains 90.0 g of NaCl per 10 liters of water What is the mole fraction and the percent composition by mass of NaCl in the saline solutions? " Excerpt From: Kaplan Test Prep. "MCAT General Chemistry Review 2021-2022." Apple Books.
mol NaCl over mol total 2/557= .003 mass NaCl over mass total 90/10090*100= .9%
normality
molarity x equivelent equivalent = how many active parts on molecule. ex: H2so4 has 2 equivilents while HCL has only 1. measure of reactive components of molecule - "Most simply, an equivalent is equal to a mole of the species of interest—protons, hydroxide ions, electrons, or ions." - concerned about concentration of reactive species -unique amoung concentration units in that it is reaction dependent ex: "acidic solution, 1 mole of the permanganate ion (MnO4−) will readily accept 5 moles of electrons, so a 1 M solution would be 5 N. However, in alkaline solution, 1 mole of permanganate will accept only 1 mole of electrons, so in alkaline solution, a 1 M permanganate solution would be 1 N."
molarity ex"If enough water is added to 11 g of CaCl2 to make 100 mL of solution, what is the molarity of the solution? " Excerpt From: Kaplan Test Prep. "MCAT General Chemistry Review 2021-2022." Apple Books.
mole cacl2: 11g/110g= .1 100ml= .1 L .1/.1= 1 M
mole fraction
moles of A/total moles of all species always equal 1 really as easy as it sounds
molality
moles of solute/ kilgrams of solvent "For dilute aqueous solutions at 25°C, the molality is approximately equal to molarity because the density of water at this temperature is 1 kilogram per liter." "You won't use molality very often, so be mindful of the special situations when it is required: boiling point elevation and freezing point depression."
endothermic solvation
new interactions weaker than original, -favored at high temperatures -most dissolutions this type ex: ammonium nitrate or sugar in water - "Because the new interactions between the solute and solvent are weaker than the original interactions between the solute molecules and between the solvent molecules, energy (heat) must be supplied to facilitate the formation of these weaker, less stable interactions"
boiling point elevation
ΔTb = iKbm "where ΔTb is the increase in boiling point, i is the van't Hoff factor, Kb is a proportionality constant characteristic of a particular solvent (which will be provided on Test Day), and m is the molality of the solution." "When a nonvolatile solute is dissolved into a solvent to create a solution, the boiling point of the solution will be greater than that of the pure solvent" "The boiling point is the temperature at which the vapor pressure of the liquid equals the ambient (incident) pressure." Excerpt From: Kaplan Test Prep. "MCAT General Chemistry Review 2021-2022." Apple Books.
