Solubility
What is the percent composition by mass of a salt water solution if 100g of the solution contains 20g of NaCl?
(20 g / 100 g) x 100% = 20% NaCl solution
The K(sp) of Ba(OH)2 is 5.0E-3. Assuming barium hydride 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): 0.5 M Ba2+ 0.1 M Ba2+ 0.05 M Ba2+
0.5 M Ba2+, ion product: [0.5][1]^2 = 0.5, IP > K(sp) = precipitation 0.1 M Ba2+, ion product: [0.1][0.2]^2 = 0.004, IP < K(sp) = dissolution 0.05 M Ba2+, ion product: [0.05][0.1]^2 = 0.005, IP = K(sp) = equilibrium
What is the vapor pressure at room temperature of a mixture containing 58 g butane (C4H10) and 172 g hexane (C6H14)? The vapor pressures of pure butane and pure hexane are 172 kPa and 17.6 kPa respectively at 25°C.
1. Calculate mole fraction 2. Calculate individual vapor pressures 3. Add vapor pressures to get total
What is the change in vapor pressure when 180 grams of glyceraldehyde (C3H6O3) are added to 0.18 L of water at 100°C?
1. Calculate the mole fraction of the solvent 2. Use Raoult's law to find the new pressure 3. Calculate initial pressure minus final pressure The vapor pressure of water at 100°C is 1 atm because that is water's boiling point
400 g AlCl3 is dissolved in 1.5 L of water at room temperature (K(b) = 0.512 Kkg/mol). How much does the boiling point increase after adding the aluminum chloride?
1. Find the van't Hoff factor 2. Determine molality 3. Plug into BPE equation 4. Add to initial temperature if finding the new temperature is required
The molar solubility of Fe(OH)3 in an aqueous solution was determined to be 4E-10 mol/L. What is the value for K(sp) for Fe(OH)3 at the same temperature and pressure?
1. Write balanced equation 2. Write the K(sp) equation 3. Sub the given molar solubility for x 4. Solve for K(sp)
What are the concentrations of each of the ions in a saturated solution of CuBr, given that the K(sp) of CuBr is 6.27E-9 at 25C? If 3g CuBr are dissolved in water to make 1L of solution at 25C, would the solution be saturated, unsaturated, or supersaturated?
1. Write the dissolution reaction equation 2. Sub x with the mole ratios 3. Solve x using given K(sp) 4. Find the number of moles in solution and compare to volume to find molarity 5. Compare IP to K(sp)
If 10 g NaOH are dissolved in 500 g of water, what is the molality of the solution?
10 g NaOH x 1 mol / 40 g = 0.25 mol NaOH m = 0.25 mol / (500 x 1 kg / 1000 g ) = 0.25 / 0.5 = 0.5 m
If enough water is added to 11 g of CaCl2 to make 100 mL of solution, what is the molarity of the solution?
11 g CaCl2 x 1 mol / 111.1 g = 0.1 mol CaCl2 M = 0.1 mol / 0.1 L = 1 M
If 184 g glycerol (C3H8O3) is mixed with 180 g water, what will be the mole fractions of the two components?
180 g water x 1 mol / 18 g = 10 moles water 184 g glycerol x 1 mol / 92 g = 2 moles glycerol 2 + 10 = 12 total moles X(water) = 10 / 12 = 0.83 X(glycerol) = 2 / 12 = 0.17
What is the molar solubility of Zn(OH)2 (K(sp) = 4.1E-17) in a 0.1 M solution of NaOH?
4.1E-17 = [x][0.1]^2 4.1E-17 = 0.001x X = 4.1E-15
What is a chelation?
A complex where the central cation is bonded to the same ligand in multiple places. Generally requires large organic ligand that can double back to form a second and even third bond with the central cation.
What is an aqueous solution?
A solution in which the solvent is water. They rely on the interactions between water molecules and solutes in solution
Describe an ideal solution.
A solution with an enthalpy of dissolution that is equal to zero. This occurs when the overall strength of the new interactions is approximately equal to the overall strength of the original interactions.
Describe Raoult's law.
Accounts for vapor pressure depression caused by solutes in solution. States that as solute is added to a solvent, the vapor pressure of the solvent decreases proportionately. Because the presence of solute molecules can block evaporation of solvent molecules but not condensation, the vapor pressure of the solution is decreased compared to the pure solvent. Ex: As more of solute B is dissolved in solvent A, the vapor pressure of solvent A decreases.
What is a complex ion?
Also called a coordination compound. A molecule in which a cation is bonded to at least one electron pair donor. The electron pair donor molecules are called ligand. The formation of these molecules is called a complexation reaction.
What is the van't Hoff factor?
Corresponds to the number of particles into which a compound dissociates in solution. Represented by i. Covalent molecules such as glucose do not dissociate readily and have a value of 1. Ex: for NaCl, i = 2 because it dissolves into 1 particle of Na and 1 particle of Cl
Compare dilute and concentrated solutions.
Dilute solutions have a small proportion of solute to solvent. Concentrated solutions have a large proportion of solute to solvent.
Define solvation.
The electrostatic interaction between solute and solvent molecules. Also called dissolution and can be called hydration when water is the solvent. Involves breaking intermolecular interactions between solute molecules and between solvent molecules and forming new intermolecular interactions between solute and solvent molecules together.
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)?
The large K(f) indicates that the formation of the product of the second reaction will be highly favorable so the CuS will ultimately be completely consumed. Therefore, the final concentration will be the same as the initial concentration of Cu2+ ions.
Define solubility.
The maximum amount of a substance that can be dissolved in a particular solvent at a given temperature. A solution is saturated when the maximum amount of solute has been added and the dissolved solute is in equilibrium with its undissolved state.
What is normality (N)?
The number of equivalents of interest per liter of solutions. Reaction dependent.
Describe freezing point depression.
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.
Describe the common ion effect.
The reduction in molar solubility of a salt when it is dissolved in a solution that already contains one of its constituent ions as compared to its solubility in a pure solvent. Molar solubility is the concentration (mol/L) at equilibrium at a given temperature. Effectively represents Le Chatelier's principle. Because the solution already contains one of the constituent ions from the products side of the dissolution equilibrium, the system will shift toward the left side, reforming the solid salt. The molar solubility of the solid is reduced, and less of the solid dissolves in the solution, although K(sp) remains constant.
Compare exothermic and endothermic solvation reactions.
The solvation is exothermic and favored at low temperatures when the new interactions are stronger than the original ones. An example is dissolution of gases into liquids (CO2 into water) The solvation is endothermic and favored at high temperatures when the new interactions are weaker than the original ones. Most dissolutions are this type. Examples are ammonium nitrate or sugar into water.
How are molality and molarity related for water? How are they related for other solvents?
They are nearly equal for water since 1 L is about equal to 1 kg so the denominators are equal. Other solvents differ significantly due to different densities.
How does Raoult's law and vapor pressure depression relate to boiling point elevation?
They go hand in hand. When a solution's vapor pressure is lowered, that means a higher temperature is required to match atmospheric pressure, thereby raising the boiling point.
How do solute molecules move in the solvent?
They move freely in the solvent and interact with it through intermolecular forces such as ion-dipole, dipole-dipole, or hydrogen bonding. Dissolved solute molecules are relatively free to interact with other dissolved molecules of different chemical identities. Chemical reactions occur easily in solution.
Define mixtures.
Two or more different chemical substances that are not chemically combined. All solutions are considered mixtures but not all mixtures are considered solutions.
Give the equation for percent composition by mass.
Used for aqueous solutions, metal alloys, and other solid-in-solid solutions. (Mass of solute / mass of solution) x 100%
400 g of AlCl3 is dissolved in 1.5 L of water at room temperature (K(f) = 1.86 Kkg/mol). What is the new freezing point of this solution?
Uses the same variables as this question for BPE ΔT(f) = iK(f)m = (4)(1.86)(2) = 15 K 273 - 15 = 258K or -15°C
How does water move relative to solute concentration in terms of osmotic pressure?
Water moves in the direction of higher solute concentration (lower water concentration). Ex: pure water will move into the NaCl solution and cause an increase in the water level on that side of a semipermeable membrane
What is the solubility of all salts containing ammonium (NH4+) and alkali metal (group 1) cations?
Water-soluble
What is the solubility of all salts containing nitrate (NO3-) and acetate (CH3COO-) anions?
Water-soluble
What is the solubility of halides (Cl-, Br-, I-) excluding Fluorides? What are the exceptions?
Water-soluble. Those formed with Ag+, Pb2+, and Hg2 2+ are the exceptions and are not water-soluble.
What is the solubility of all salts of the sulfate ion (SO4 2-)? What are the exceptions?
Water-soluble. Those formed with Ca2+, Sr2+, Ba2+, and Pb2+ are the exceptions and are not water-soluble.
Describe boiling point elevation.
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 defined as the temperature at which the vapor pressure of the liquid is equal to the ambient pressure.
Give the equation for change in boiling point.
ΔT(b) is the increase in boiling point (not the boiling point itself) i is the van't Hoff factor K(b) is the proportionality constant characteristic of a particular solvent (will be given) m is the molality of the solution
Give the equation for freezing point depression.
ΔT(f) is the freezing point depression i is the van't Hoff factor K(f) is the proportionality constant characteristic of a particular solvent (will be given) m is the molality
Give the equation for osmotic pressure.
Π is the osmotic pressure i is the van't Hoff factor M is the molarity R is the ideal gas constant T is the temperature
How does entropy change affect the spontaneity of dissolution?
At constant temperature and pressure, entropy always increases upon dissolution. Depends on Gibbs free energy change.
What does the value of K(sp) say about the types of bonds in a complex ion?
Complex ions contain multiple polar bonds between the ligand and the central metal ion and therefore should be able to engage in a very large amount of dipole-dipole interactions. This stabilizes their dissolution and causes a very high K(sp) value meaning the compound is stable
What holds together complexes?
Coordinate covalent bonds in which an electron donor (Lewis base) and an electron pair acceptor (Lewis acid) form very stable Lewis acid-base abducts. Important for biological molecules such as hemoglobin, cobalamin (vitamin B12)
What does the spontaneity of dissolution depend on?
Enthalpy and entropy change for the solute and solvent of the system
If you mix 180 g of the following compounds in 250 L of water, what are their concentrations in molality, molarity, and normality (for acid-base chemistry)? Glucose (180 g/mol) Carbonate (60 g/mol)
Glucose: 0.004 m, 0.004 M, 0.004 N Carbonate: 0.0012 m, 0.0012 M, 0.024 N
Define solutions.
Homogenous mixtures of two or more substances that combine to form a single phase, usually the liquid phase. Can also be formed from different combinations of the three phases of matter. Consists of a solute dissolved in a solvent. The solvent is the component of the solution that remains in the same phase after mixing or is present in the greater quantity of they are already in the same phase.
Give the equation for Raoult's law.
P(A) is the vapor pressure of solvent A when solutes are present X(A) is the mole fraction of the solvent A in the solution P(A)° is the vapor pressure of solvent A in its pure state
Compare the IP and K(sp) values and whether that indicates an unsaturated, saturated, or supersaturated solution.
IP < K(sp) : undersaturated. Solute will continue to dissolve (thermodynamically favored) IP = K(sp) : saturated. Solution is at equilibrium. Molarity at this stage is called the molar solubility IP > K(sp) : supersaturated. Precipitation will occur. Can be accomplished by heating and then cooling the solution. Thermodynamically unstable.
What is the ion product?
IP. Analogous to the reaction quotient, Q, for other chemical reactions. Calculated to determine whether a solution has reached saturation. Same formula as K(sp) except the concentrations used in this equation are the concentrations of the ionic constituents at that given moment in time, not at equilibrium. IP = [A^n+]^m[B^m-]^n
What determines if a solute is soluble or insoluble?
If the change in Gibbs free energy is negative, the process is spontaneous and soluble. If the change in Gibbs free energy is positive, the process in nonspontaneous and insoluble. If a solute has a molar solubility above 0.1 M in solution, it is generally considered soluble. Sparingly soluble salts dissolve minimally and have a molar solubility below 0.1 M.
What is the solubility of all carbonates (CO3 2-), phosphates (PO4 3-), sulfide (S2-), and sulfites (SO3 2-)? What are the exceptions?
Insoluble. Those formed with the alkali metals and ammonium are the exceptions and are water-soluble.
What is the solubility of all hydroxides? What are the exceptions?
Insoluble. Those formed with the alkali metals, ammonium, Ca2+, Sr2+, ad Ba2+ are the esceptions and they are water-soluble.
What is the solubility of all metal oxides? What are the exceptions?
Insoluble. Those formed with the alkali metals, ammonium, and CaO, SrO, and BaO are the exceptions and hydrolyzes to form solutions of the corresponding metal hydroxides.
What is the solubility product constant?
K(sp) = [A^n+]^m[B^m-]^n Ex: for AgCl, K(sp) = [Al+][Cl-]
Give the equation for molarity (M) of a solution.
M = moles of solute / liters of solution
Give the equation for finding the concentration of a diluted solution.
M(i)V(i) = M(f)V(f)
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?
M(i)V(i) = M(f)V(f) V(i) = ( M(f)V(f) ) / M(i) (1.1)(300) / (5.5) = 60 mL
Describe the K(sp) formula for sparingly soluble salts of the following general formulas: MX MX2 MX3
MX: K(sp) = x^2 MX2: K(sp) = 4x^3 MX3: K(sp) = 27x^4 X is the molar solubility assuming no common ion effect
What are the conditions in which Raoult's law applies?
Only when the attraction between the molecules of the different components of the mixture is equal to the attraction between the molecules of any one component in its pure state. Solutions that obey Raoult's law are called ideal solutions.
Define colligative properties. What are some examples associated with dilute solutions?
Physical properties of solutions that are dependent on the concentration of dissolved particles but not on the chemical identity of the dissolved particles. Vapor pressure depression, boiling boing elevation, freezing point depression, and osmotic pressure.
What is one way in which solubility of a compound can be increased?
Solids can increase solubility buy increasing the temperature. Gases can increase solubility by decreasing temperature and increasing pressure.
Define entropy.
The degree to which energy is dispersed throughout a system or the amount of energy distributed from the system to the surroundings at a given temperature. Can also describe the molecular disorder or number of energy microstates available to a system at a given temperature. Given by symbol S.
Compare the change in Gibbs free energy for spontaneous and nonspontaneous processes.
Spontaneous = -ΔG Nonspontaneous = +ΔG
How does the solubility product constant change with temperature changes?
Temperature dependent. Also depends on pressure when a gas is dissolve in a liquid. Generally increases with increasing temperature for non-gas solutes and decreases for gas solutes. Higher pressures favor dissolution of gas solutes so the K(sp) will be larger for gases at higher pressures than at lower ones.
What factors effect solubility?
Temperature of the solution, the solvent, and pressure for a gas-phase solute. Also affected by the addition of other substances to the solution. Complex ions typically do not increase solubility of a substance.
Define osmotic pressure.
The "sucking" pressure generated by solutions in which water is drawn into a solution. The amount of pressure that must be applied to counteract this attraction of water molecules for the solution.
What is the formation or stability constant?
The K(sp) value of the complex ion itself when used in a mixture of solutions. Given by K(f). Usually significantly larger than the K(sp) of the compound providing the metal ion —> initial dissolution of metal ion is the rate-limiting step of complex ion formaiton
Define concentration.
The amount of solute dissolved in a solvent. Described by many different units
The K(sp) of AgI in aqueous solution is 8.5E-17. If a 1E-5 M solution of AgNO3 is saturated with AgI, what will be the final concentration of the iodide ion?
The concentration of Ag from the AgNO3 solution adds to the unknown concentration of Ag. X is negligible since it is so small.
Give the equation for mole fraction (X).
X(a) = moles of a / total moles of all species The sum of the mole fractions in a system will always equal 1.
Give the equation for molality (m) of a solution.
m = moles of solute / kilograms of solvent For dilute aqueous solutions at 25C , the molality is approximately equal to molarity bc the density of water at this temp is 1 kg/L. Usually only used for boiling point elevation and freezing point deoression
