Chemistry II - Chapter 11 Colligative Properties, Mole Fraction and Molality

What is the mole fraction of potassium dichromate, K2Cr2O7, in a solution prepared from 24.42 g of potassium dichromate and 240. g of water? Report your answer in scientific notation with three significant figures.

$\text{X =}\ 6.19\times10^{-3}$X = 6.19×10−3​ To find the mole fraction we use: mol K2Cr2O7=24.42 g K2Cr2O7×1 mol K2Cr2O7294.181 g=0.08301 mol K2Cr2O7mol H2O=240. g H2O×1 mol H2O18.015 g H2O=13.3 mol H2OXK2Cr2O7=mol K2Cr2O7total mol=0.08301 mol K2Cr2O713.4 total mol=6.19×10−3

What is the molar mass of a protein if a 0.30 L of solution containing 0.45 g of the protein has an osmotic pressure of 0.80 torr at 25∘C?

3.5x10^4

When a solution with a nonvolatile solute is prepared, which of the following will DEFINITELY decrease relative to the pure solvent? Select all that apply. Select all that apply: Freezing point of solution Vapor pressure of solution Boiling point of solution All of the above

Freezing point of solution Vapor pressure of solution The vapor pressure and freezing point will be lower than that of the solvent when a nonvolatile solute is introduced, while the solution's boiling point will be higher.

Which of the following is true as a result of an increase in osmotic pressure of an aqueous solution that is separated from a compartment of pure water by a semipermeable membrane?

The tendency for water to move by osmosis into the aqueous solution is increased. Increasing the osmotic pressure of the solution means that there is now an even greater difference in osmotic pressures of the solution (higher osmotic pressure) and the pure water (lower osmotic pressure). The increase in that difference increases the tendency for water to move by osmosis into the solution.

Consider two aqueous nonvolatile and nonelectrolyte solutions, each with a solute concentration of 1 M. One contains glucose, while the other contains an unidentified covalent solid. Which of the following are sure to be identical in each solution? Select all that apply: Their freezing points The identity of the solvent The identity of the solute Their densities

Their freezing points The identity of the solvent These solutions have the same concentration and therefore the same freezing point. The solvent is water in each. However, because density depends on the type of solute in a solution (and the solute is different in each), their densities are almost certainly not the same.

Three aqueous solutions of different volumes are prepared. One is 3 M in glucose, one is 3 M in fructose, and one is 3 M in sucrose. Which of the following must these solutions have in common?

They have the same boiling points. These solutions all have equal concentrations BUT, since the volumes are different, the moles of solute cannot be the same. We do not know the densities of each, and we also cannot assume that they contain equivalent masses of solute, because the molar mass of each solute is different. However, because their concentrations are equal, their boiling points will be elevated by the same amount (as boiling point is a colligative property).

Three solutions in ethanol are prepared: one by dissolving 0.010 moles of solid vanillin in 3.0 L of solvent, one by dissolving 0.010 moles of solid trimyristin in 3.0 L of solvent, and one by dissolving 0.010 moles of an unknown salt in 3.0 L of solvent. What do these solutions have in common? (Assume the volume of the solution is unchanged by the addition of solutes and that the salt does not dissociate to any significant extent in ethanol). Select all that apply.

They have the same freezing point. Their vapor pressures are the same. Since the number of moles and the volume of each solution is given it is possible to calculate the concentration of the solution. Since the units of concentration are moles/L, 0.010 mole is divided by 3.0 L. This gives a concentration of about 0.0033 M . Since Vapor pressure lowering and freezing point depression are colligative properties, and the concentrations of each of these solutions are the same, their vapor pressures and freezing points will be identical. However, because each solute has a different molecular weight, they will contain different masses of solute.

The change in boiling point for a solution is always: Select the correct answer below: added to the normal boiling point subtracted from the normal boiling point multiplied by the normal boiling point depends on the solute

added to the normal boiling point The presence of solute will always increase the boiling point of the solution, so the change in boiling point must be added to the normal boiling point.

The change in boiling point for a solution does NOT depend on: Select the correct answer below: molecular mass of the solute size of solute particles chemical identity of the solute all of the above

all of the above None of these are parameters that affect the boiling point of a solution.

Another term for the freezing point depression constant is the: Select the correct answer below: proportionality constant ebullioscopic constant cryoscopic constant none of the above

cryoscopic constant The cryoscopic constant and the freezing point depression constant are synonymous.

Which of the following terms describes the extracellular fluid in a healthy human?

isotonic An isotonic solution is one that has the same overall solute concentration (and therefore the same wateriness) as a cell that's immersed in that solution. Because of equal wateriness (equal osmotic pressures), water enters and leaves the cell at the same rate, so the volume of the cell remains constant, and the cell does not undergo crenation or lysis.

The partial pressure of a solution component will always be: Select the correct answer below: less than its vapor pressure in pure form more than its vapor pressure in pure form equal to its vapor pressure in pure form depends on the substance

less than its vapor pressure in pure form Because the vapor pressure in pure form is being multiplied by the mole fraction, and the mole fraction must always be between zero and one, we will always get a partial pressure that is some fraction of the vapor pressure in pure form.

In order for a solute to decrease the vapor pressure of the solution, the solute must be: Select the correct answer below: ionic covalent volatile nonvolatile

nonvolatile The identity of the solute is irrelevant, except that it must be nonvolatile in order to hinder the vaporization of solvent particles. Nonvolatile refers to a substance that does not readily evaporate into a gas under existing conditions. If it were volatile, the solute particles would also vaporize which would increase the vapor pressure of the solution.

Which will freeze at the lowest temperature? pure bottled water tap water ocean water these will freeze at the same temperature

ocean water Ocean water has the highest concentration of solute, so it will have the greatest freezing point depression, and therefore freeze at the lowest temperature of the three.

Colligative properties can be observed because the presence of solute particles obstructs: Select the correct answer below: physical processes chemical processes expansion contraction

physical processes Colligative properties are typically observed during things like phase changes, which are exclusively physical processes.

The boiling point elevation constant:

will change for every solvent Boiling point elevation is a colligative property. Colligative properties depend on the identity of the solvent, but not the identity of the solute - only its concentration, because they are largely phenomena related to the separation between solvent molecules caused by the presence of solute. The boiling point elevation constant does depend on the identity of the solvent because it depends on the strengths of interactions between solvent molecules.