Chapter 13
Normality
# of equivalents/ Liter solution
What is Henry's Law and what is it used to calculate?
(used to calculate the partial VP of the solute) Vapor Pressure of solute = (mole fraction of solute) * (Henry's Law Constant).
What 3 things should you remember about Ksp (and all other equilibrium constants)?
1) Leave out pure liquids and pure solids (this will make all Ksp equations one line only. If you have something in the denominator of a Ksp equation, you've made a mistake). 2) Temperature is the only thing that changes Ksp 3) Ksp can only be measured for a saturated solution. This is because saturation is the point at which the dissolution reaction has reached equilibrium. In other words, it's just like all other Ks; you can't measure them anywhere other than equilibrium either.
What 2 ways can you solve ideal gas law problems?
1) Manipulating equations: 2) P1V1/T1 = P2V2/T2
How do you calculate solubility?
1) Write out the Ksp expression 2) Substitute into the expression the value given for Ksp. 3) Substitute x into the equation for each ion, using 2x, 3x, etc., If more than one mole of each ion is produced (Hint: Ask yourself, "If x moles of the reactant are dissolved, how many moles of each ion will be produced?). 4) Solve for x. Your answer, "x" is the "solubility" of that particular specie.
ppm
= mass solute/total mass solution * 10^6 (for ppb multiply by 10^9)
A certain mixture has a large negative heat of solution. Describe the relative strength of 1) the intermolecular forces between solvent molecules 2) the intermolecular forces between solute molecules 3) the intermolecular forces between solute and solvent molecules
A certain mixture has a large negative heat of solution. Describe the relative strength of 1) the intermolecular forces between solvent molecules: weaker than bond between solute and solvent molecules 2) the intermolecular forces between solute molecules: weaker than bond between solute and solvent molecules 3) the intermolecular forces between solute and solvent molecules: Because of the large negative Heat of solution, this means that the bond between solute and solvent molecules is stronger and more stable than the bond between just solute molecules and just solvent molecules.
Osmotic Pressure
A measure of the tendency of water to move from one solution to another across a semi-permeable membrane.
The Ion Product( Solubility Product)? What is it similar to?
Also referred to as the "Solubility Product". Essentially, this is the same thing in relationship to Ksp and Q is in relationship to Keq. Plug in the values for the actual concentrations of each species at some point other than equilibrium (i.e., for an unstaturated or supersaturated solution). If the product is greater than Ksp, you know precipitate will form. If it is less than or equal to Ksp, then you know that no precipitate will form. If the ion product happens to be exactly equal to Ksp, then the solution must be exactly saturated (i.e., at equilibrium).
Aqueous
An aqueous solution is any solution in which water is the solvent. Something that is hydrated is said to be in an aqueous phase.
Define "spectator ion"
An ion that exists as a reactant and a product in a chemical reaction. It does not participate in the reaction hence "spectator."
When would you expect the slope of the graph to be greater for a heating curve representative of water? : Between the solid and liquid phase or between the liquid and gas phase? Why?
Between the liquid and gas phase. • Ice, melts more easily because of the structure of ice. Ice holds a hexagonal lattice work which includes molecules moving apart and H-bonds reaching their maximum number. With the ice having a lower density and a higher surface area, the heat of another object is more apt to affect the ice. o It is easier to break the bonds in ice than in water. Therefore more energy is required to vaporize water than to melt ice.
ΔT = (kb)(m)(i)m*i
Boiling point elevation. When calculating bp elevation with this equation, the answer you get is a change in bp from the normal. not the actual bp. To get the new bp or fp, add or subtract your answer from the normal bp of fp. Of course if specifically asked for the change then your first number would be correct.
Boiling Point Elevation When is boiling point elevated
Bp is elevated when a non-volatile solute is added according to: o ΔT = kb*m*i; where kb is a constant, m is molality (NOT molarity) and 'i' is the number of ions formed per molecule (i.e., for NaCl i=2; for CaCl2 =3).
Describe the Common Ion Effect
Common-ion effect describes the suppressing effect on ionization of an electrolyte when another electrolyte is added that shares a common ion.
How does the addition of a non-volatile solute affect vapor pressure?
Decreases vapor pressure a nonvolatile solute does NOT readily vaporize.
Solution?
Definition: A solution is a homogenous mixture of two or more compounds in the same phase (We usually think of all solutions as being in the liquid, or "aqueous" phase; however, a homogenous mixture of gases is also called a "solution."
Gas --> Solid
Deposition
What happens to entropy when a solution forms
Entropy increases
Solution Formation: What has to happen in order for a solution to form?
For a solution to form, the intermolecular forces between the solute particles must first be broken; then any intermolecular forces between the solvent particles must be broken (to make room for the solute). Finally, new intermolecular forces are formed between the solute particles and the solvent particles.
Freezing Point Depression. When is freezing point Depressed
Fp is depressed when a non-volatile solute is added according to: o ΔT = kf*m*i; where kf is a new constant different than kb above.
Liquid --> Solid
Freezing
ΔT = (kf)(m)(i)
Freezing point depression. When calculating fp elevation with this equation, the answer you get is a change in fp from the normal. not the actual fp. To get the new bp or fp, add or subtract your answer from the normal bp of fp. Of course if specifically asked for the change then your first number would be correct.
Condensation
Gas --> Liquid
What does a +ΔH solution mean? How do you get a +ΔH solution?
If the new intermolecular forces are not more stable than the old ones, the solution has a +ΔH solution. A positive Heat of Solution means that energy must be added to make the solute dissolve.
How does the addition of a volatile solute affect vapor pressure?
Increases vapor pressure because of the readily vaporized volatile solute.
Clarify the difference between solubility and the solubility constant.
Ksp describes a ratio of products to reactants at the saturation point. Solubility is the actual mols/L that can be dissolved.
What do the lines on a phase diagram represent?
Lines on a phase diagram represent a point where the two phases on either side of the line are in equilibrium.
When does a liquid boil?
Liquid boils when it is heated to its boiling point, which is the temperature at which the vapor pressure of the liquid is equal to the pressure exerted on the liquid by surrounding environmental pressure. So basically a liquid boils when its vapor pressure is equal to the atmospheric pressure.
Solid -> Liquid
Melting
What characteristics to Molecules in the same phase share?
Molecules of the same "phase" a) are in the same state (i.e., liquid, solid, or gas), b) have the same chemical composition, and c) are structurally homogeneous
Do different phases of the same substance have the same specific heat capacity? Why or why not?
No. For example if you look at ice and water, they have different heat capacities because one is solid and the other liquid. In solid form a molecule is restricted by how many ways it can move without breaking the structure. in liquid form it has more directions to move and can there for absorb more energy before change form which is what specific heat capacity is all about. You must also take into account the different bonds between the water molecules is solid vs liquid form and the fact that ice contains air as well as water.
What will happen if a spectator ion is added to the same solution?
Nothing. A spectator ion just "sits and watches". (example Na)
Be sure you understand what phases are or are NOT present at the triple point vs. the critical point.
Phases at the Triple Point: solid, liquid, gas Phases at the Critical Point. liquid, gas
A traditional phase diagram has what on the y axis?
Pressure!!!! Temperature is on the x axis
Ksp
Solubility constant Exactly the same thing as Keq, Ka, and Kb.
What is the difference between STP and standard conditions?
Standard Conditions usually indicates 25˚C plus several other agreed-upon conditions at which thermodynamic data are always measured
Solid-->Gas
Sublimation
ΔH vaporization
The amount of energy in Joules required to go from a Liquid to a gas OR the energy that must be removed to go from gas to liquid. Again, it describes both evaporation and condensation
ΔH fusion
The amount of energy in Joules required to go from solid to liquid OR the energy that must be removed to go from liquid to solid. This describes the transition in
Critical Point
The critical point or critical state is the point at which two phases of a substance initially become indistinguishable from one another.
Hydration Number
The number of water molecules needed to surround an ion )varies according to the size and charge of the ion)
Solvent vs. Solute
The one you have the most of is your solvent and the one you have the least of is your solute.
The ratio given by PV/RT tells us which of two Ideal Gas Law assumptions is the major cause of the deviation from an Ideal gas If PV/RT > 1 it is due mostly to the ? If PV/RT < 1 it is due mostly to the ?
The ratio given by PV/RT tells us which of two Ideal Gas Law assumptions is the major cause of the deviation: If PV/RT > 1 it is due mostly to the molecular volume assumption If PV/RT < 1 it is due mostly to the intermolecular forces assumption
What do the various positive slopes on a heating curve represent? (Notice that they are usually different between phase changes)
The slopes represent the average change in kinetic energy, or the average change in temperature. The definition in temperature is average kinetic energy. The slope for the liquid to gas phase is larger than the slope for the solid to liquid phase, because more energy is required to change a liquid to a gas than a solid to a liquid.
Critical Temperature
The temperature at a substance's critical point
Where do you apply the saying "Like dissolves like" ?
This phrase refers to the fact that polar substances are soluble in polar solvents and non-polar substances re soluble in non-polar solvents. Polar and non-polar substances do NOT form solutions.
Precipitate
To form an insoluble compound either by reacting to salts or by changing the temperature to affect the solubility of the compound. Name given to the solid that is formed as the result of a precipitation reaction.
Vapor Pressure
Vapor Pressure (VP) is the partial pressure of the gaseous form of a liquid that exists over that liquid when the liquid and gas phases are in equilibrium.
How is vapor pressure affected by temperature?
Vapor pressure increases as temperature increases.
Hydration
When several water molecules attach to one side of an ionic compound, they are able to overcome the strong ionic bond, and break apart the compound. This process is called hydration.
Unsaturated Solution
a chemical solution in which the solute concentration is lower than its equilibrium solubility.
Solubility
a solute's tendency to dissolve in a solvent.
Supercritical Fluid
a substance in a thermodynamic state where temperature and pressure are above the substance's critical point
What common compounds are insoluble? (unless paired with something always soluble)
carbonate, phosphate, silver (Ag), mercury (Hg) and lead (Pb) Gases
Conceptualize Dalton's Law of Partial Pressures
if we add more of Gas 1 (P1) to an existing mixture of the three gases, we have increased the partial pressure of Gas 1 and the total pressure, but have had zero effect on the partial pressure of the other gases. Partial pressure is NOT similar to a mole or mass fraction. By adding more of Gas 1 we did decrease the mole fraction of Gases 2 and 3, but we did NOT decrease their partial pressures.
What does it mean if your ion product is greater than your Ksp?
it means precipitate will form.
Evaporation
liquid --> Gas
Mass percent
mass solute/total mass of solution * 100
Molarity
moles solute/Liter solution
What common compounds are soluble?
nitrate, ammonium, and all the alkali metals (GroupIA)
What does a -ΔH solution mean? How do you get a -ΔH solution?
o If the new intermolecular forces formed are greater (i.e., stronger, more stable) than the sum of the intermolecular forces that had to be broken, the net energy is released and the solution is said to have a -ΔH solution. A negative Heat of Solution means that the dissolution process is exothermic and heat will be evolved. No energy required for a solute to dissolve.
Critical Pressure
pressure at a substance's critical point
What is the section to the far upper left hand corner represent on a phase diagram? How do you name the phases going clockwise from that phase?
solid phase solid-->liquid--> gas
Melting point
the temperature at which a substance changes from a solid to a liquid o solid and liquid phases exist in equilibrium
Boiling point
the temperature at which the vapor pressure of the liquid equals the pressure surrounding the liquid & the liquid changes to a vapor.
What is Raoult's Law and what is it used to calculate?
used to calculate partial Vp of the solvent Vapor Pressure w/ a Non-Volatile Solute = (mole fraction of the pure solvent) * (VP of the pure solvent) Vapor Pressure w/ a Volatile Solute = (mole fraction of the pure solvent) * (VP solvent) + (mole fraction of the solute )*(VP of the Solute).
How do you calculate ΔH from a heating curve?
ΔH fusion = The change in q (x-axis) during the phase change from solid to liquid ΔH vaporization = The change in q (x-axis) during the phase change from liquid to gas
At STP What do each of the following equal? • P = ? • V = ? • n = ? • R = ? • T =?
• P = 1 atm • V = 22.4 mL • n = 1 mole • R = 0.0821 L*atm/mol*K • T =273 K (0˚C)
What is Standard Temperature and Pressure (STP)?
A set of standard conditions true of any ideal gas said to be "at STP." For the MCAT, unless you are specifically told otherwise, assume that all gases are ideal and start out at STP. At STP: • P = 1 atm • V = 22.4 mL • n = 1 mole • R = 0.0821 L*atm/mol*K • T =273 K (0˚C)
Saturated Solution
A solution containing the maximum concentration of a solute. Additional solute will not dissolve in a saturated solution. o A solution where the rate of dissolution and precipitation are equal.
Supersaturated Solution
A solution that contains a higher than saturation concentration of solute
A student working in the lab accidentally spills an unknown amount of sodium chloride into a beaker containing 100mL of a standardized 1.5 M sodium chloride solution. All of the following could result from the accidental addition EXCEPT: A) The freezing point of the standardized solution will decrease B) The boiling point of the standardized solution will increase. C) The melting point of the standardized solution will decrease. D)Sodium chloride crystals may precipitate.
Adding a solute to a solution will always decrease the freezing point, making answer A plausible. Adding solute to a solution decreases the vapor pressure and increases the boiling point, making B also plausible. Answer C is equivalent to Answer A because fp=mp. Answer D is not plausible and is therefore the correct answer. According to Le Chatelier's principle, adding more NaCl will shift the dissolution equilibrium to the right.
What are colloids? What are they NOT? What physical properties do they have?
Colloids are NOT solutions Colloids are solvents containing undissovled solute particles that are too small to be separated by filtration, but are much larger than the solute particles in a true solution. Colloids scatter light, while true solutions do not. Examples of colloids include paint (a suspension of solid paint crystals in a solvent) and dust floating in air.
Why don't gas molecules eventually lose their energy s a result of constantly colliding with one another?
Conservation of energy and momentum
Container A is a sealed reaction vessel containing 8.0 moles of hydrogen gas and 2.0 moles of chlorine gas. Container B is a sealed reaction vessel containing 2.0 moles of hydrogen gas and 8.0 moles of chlorine gas. If the gas mixtures in both containers behave as ideal gases, which of the following is true? (Note: Assume both containers are of equal volume and experience identical ambient temperatures) A) The pressure inside Container B will be greater than the pressure inside Container A B) The pressure inside Container B will be less than the pressure inside Container A. C) The total number of moles of gas inside Container A is greater than the total number of moles of gas inside Container B D) The pressure inside both containers will be exactly equal.
D By definition, any ideal gas behaves in an identical manner, regardless of the actual gas molecule present. In other words, even though chlorine gas is a larger, heavier gas than hydrogen gas, they both are treated as identical "ideal" gas particles. for this reason any ideal gas problem generally has to do only with the moles of gas present and nothing to do with the identity or molar mass of the individual gas molecules. In this case, therefore, D is Correct.
Molarity (M) changes w/ temperature, but molality (m) does not. Provide a possible explanation. (Hint: what happens to volume when temperature increases?)
Molality is not dependent on temperature change. 1) Molality is moles per kilogram of solvent. The mass of the solvent does not change with changes in temperature. 2) Molarity is moles per liter of solution. The solution can expand or contract as the temperature changes, thus affecting the volume and the concentration.
Does temperature change during a phase change? Why or Why Not?
NO. There is no change in temperature during a phase change. The fact that heating curves are flat (i.e., horizontal, slope = 0) during the actual phase change demonstrates the following frequently-tested MCAT principle: Once a phase change starts, all of the energy goes into breaking intermolecular forces and none goes toward an increase in temperature.
Π=iMRT Π=(p*g*ha )-(p*g*hb)
Osmotic pressure.
What is the ideal gas law and what assumptions are made?
PV = nRT Ideal Gas Assumptions: 1) Gas molecules have no volume 2) No intermolecular forces exist between gas molecules 3) All collisions are perfectly elastic 4) Average KE is exactly proportional to temperature
why in ppm do we times the mole fraction by a million?
Parts per million (ppm) is NOT a measure of how many solute particles there are per 1 million total particles. This is how most students erroneously think of it. It is nothing more than mass percent multiplied by 10^4, or "mass fraction" multiplied by 10^6. The purpose of multiplying by 1 million is to make very, very small concentrations easier to work with.
Triple Point
The temperature at which a solid, liquid, and gas phases, coexist in equilibrium.
For the majority of substances at their triple point, increasing temperature at constant pressure will result in which of the following transformations: A) gas, liquid and solid to gas only B) gas and liquid to solid only C) gas, liquid and solid to liquid only D) supercritical fluid to gas only
The triple point is the pace on a phase diagram where all three lines converge. At that point the substance exists as a mixture of gas, liquid, and solid all in equilibrium with one another. An increase in temperature will move the substance to the right on the phase diagram into the gas portion of the diagram. This makes A the best choice.
What do the horizontal sections of a heating curve graph represent?
They the first plateau in the heating diagram represents the melting point. Temperature is staying the same. The second plateau represents the boiling point. Temperature here is also staying the same. In both cases temperature stays the same because all of the energy is going into the breaking of bonds, rather than the change in temperature.
Increasing the temperature decreases the solubility for what?
gases
Heating Curves
graph of heat (q) in Joules vs. temperature (T) in Kelvin or Celsius.
When deciding which substance will elute first do you look for the one with the highest boiling point or the lowest boiling point?
lowest boiling point.
Mole fraction
moles of solute/total moles of solution (solute + solvent)
Molality
moles solute/ Kg solvent
Non-volatile
nonvolatile refers to a substance that does NOT readily vaporize into a gas under existing conditions.
What is the relationship between heat of solution and vapor pressure?
o A positive heat of solution leads to an increase in vapor pressure o A negative heat of solution leads to a decrease in vapor pressure.
What is the difference between Effusion and Diffusion
o Diffusion: The process by which gas molecules spread from areas of high concentration to areas of low concentration due to the random motion imparted to them as a result of their kinetic energy and collisions with other molecules. o Effusion: The diffusion of gas particles thru a pin hole. A pin hole is defined as a hole smaller than the average distance a gas molecule travels between collisions.
What is Graham's Law?
o E1/E2 = √(MW2)/√(MW1) MW=molar weight E1 and E2 can represent either the effusion rate or the diffusion rate of gases 1 and 2, respectively. Notice that the rate of effusion or diffusion is inversely proportional to the molecular weight of the gas.
Gas Solubility? Is it similar or different from liquids?
o Gas solubility is the exact opposite of solubility of liquids and solids. For gases, increased temperature decreases solubility and decreased temperature increases solubility. o Increasing the VP of gas X over a liquid increases the solubility of gas X in that liquid. (This is why they pressurize soda pop cans with excess CO2)
What are the general characteristics of Gases? (Name 5)
o Gases are far less dense than liquids or solids o They contain much weaker intermolecular attractions than do liquids or solids. o Gas molecules are very far apart. o Gas molecules move very fast and collide billions of times per second. o Gases are always miscible, regardless of their polarity. (miscible = soluble, able to be mixed to form a solution)
Dalton's Law of Partial Pressures
o Ptotal = P1 + P2 + P3 +...
Volatile
refers to a substance that vaporizes readily. o Volatility is a measure of how readily a substance vaporizes.
