# CHEM125 – CHAPTER 12 – BASIC HOMEWORK

## CHAPTER 12 BASIC HOMEWORK

(Go to Chapter 13 Explanation Provided) Click Here

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### Question 1

What is the molarity of a sodium chloride solution, if 13.28 g of NaCl are dissolved in enough water to make 0.500 L of solution? ### Question 2

What is the molality of a sodium chloride solution, if 11.12 g of NaCl are dissolved in 0.700 kg of water? Hint given in general feedback ### Explanation

Convert g NaCl to moles and divide by the kg of water to get the molality. Units: m (but don’t include in answer).

### Question 3

What is the mole fraction of a lithium fluoride solution prepared by dissolving 38.5 g of LiF in 0.800 kg of water. Hint given in general feedback ### Explanation

Calculate the moles of LiF and water. Divide the number of moles of LiF by the total number of moles. Did you remember to convert kg to g?

### Question 4

What is the mass percent of a lithium fluoride in a solution prepared by dissolving 37.0 g of LiF in 0.700 kg of water. Hint given in general feedback ### Explanation

Divide the mass of LiF by the total mass and multiply by 100%. Did you remember to convert kg to g?

### Question 5

Calculate the freezing point for a 1.55 m solution of CCl4 in benzene. Help: Solution freezing point ### Question 6

Calculate the increase in the boiling point,ΔT, for a 1.35 m solution of sucrose (dissolves as a molecule) in water. ### Question 7

Sugar is dissolved in hot water at 45oC until the mole fraction of water decreases to 0.896. The vapor pressure of pure water at this temperature is 72 torr. What is the vapor pressure (in torr) of water for this solution? Help: Colligative properties of gases ### Question 8

18.0 g of the nonvolatile solute urea (M.W. = 60.06 g/mol) is dissolved in 194 g of water at 60oC. The vapor pressure of pure water at this temperature is 149 torr. What is the equilibrium vapor pressure (in torr) of water for this solution? Hint given in general feedback. ### Explanation

To calculate the mole fraction of water, first calculate the moles of water and urea. Then divide the number of moles of water by the total number of moles.

### Question 9

Which 0.06 m aqueous solution (in water) should have the greatest increase in boiling point?

Select one: ### Question 10

Calculate the freezing point for a 4.20 m aqueous solution of NaCl.  ### Question 11

A 0.200 g sample of a nonvolatile yellow crystalline solid is dissolved in 15.1 g of benzene, producing a solution that freezes at 5.01oC. Find the molar mass of the yellow solid in g/mol.  ### Question 12

A 2.60 g sample of a nonvolatile nonelectrolyte blue crystalline solid is dissolved in 47.1 g of acetic acid, producing a solution that bolis at 119.6oC. Find the molar mass of the blue solid in g/mol. Hint given in feedback ### Explanation

Use the same procedure as in the last problem except now ΔTb = mkb.

### Question 13

At a certain temperature the vapor pressure of pure benzene and pure toluene are 380 torr and 130 torr, respectively. If the mole fraction of benzene is 0.42, what is the total vapor pressure. Help: Vapor pressure ideal liquids ### Question 14

At a certain temperature the vapor pressure of pure benzene and pure toluene are 380 torr and 130 torr, respectively. If 2.60 mol benzene is mixed with 4.76 mol toluene, what is the total vapor pressure. ### Question 15

Which of the following pairs of molecules are expected to obey Raoult’s law?

Select one or more:   ### Question 16

What is the osmotic pressure in atm of a 0.870 M solution of sugar at 25oC? Help: Osmotic pressure ### Explanation

Did you remember to use K?

### Question 17

What is the osmotic pressure in atm of a 0.183 M solution of NaCl at 0oC? Hint given in feedback ### Explanation

You must use the molarity of particles. Remember NaCl is a strong electrolyte. This is equivalent to π = (Mi)RT where i is the van’t Hoft factor. Because NaCl is a strong electrolyte it breaks apart into Na+ ions and Cl when it dissolves in water. Thus each NaCl produces two particles when dissolved in water and the van’t Hoff factor is 2.