1,001 Chemistry Practice Problems For Dummies (2014)

Part I. The Questions

Chapter 13. Solutions (The Chemistry Kind)

Solutions contain a solvent and one or more solutes. The concentration is the quantity of solute in a given amount of solution. Concentrations are important when considering colligative properties, which depend on the number of solute particles present, not on their identities. Freezing point depression, boiling point elevation, and osmotic pressure are examples of colligative properties.

The Problems You’ll Work On

In this chapter, you work with solutions in the following ways:

check Identifying solution components

check Calculating small concentrations (ppt, ppm, ppb)

check Diluting solutions

check Finding molarity and molality

check Determining freezing point depression and boiling point elevation

check Finding osmotic pressure

Note: For reference, you can find the periodic table in the Appendix.

What to Watch Out For

Remember the following when working on solutions:

check Water is a very important solvent, but it isn’t the only solvent.

check Conversion from one concentration unit to another is easier through dimensional ­analysis.

check Molality is the only concentration unit that has the solute in the denominator.

check Molality (m), not molarity (M), is used for freezing point depression and boiling point elevation.

check All colligative properties depend on the total particles present in the solution, not their identities.

check The freezing point of a solution is the normal freezing point of the solvent minus the depression value. The boiling point of a solution is the normal boiling point of the solvent plus the elevation value.

Solutions, Solvents, and ­Solutes

862–871 The following questions concern terms associated with solutions.

862. For all solutions, what is a solute?

863. For all solutions, what is a solvent?

864. Air is a solution. What is the solvent?

865. High-carbon steel is a solution. What is the solvent?

866. Vodka is a solution. A sample of 80-proof vodka is 40% alcohol. What is the solvent?

867. Some sodium chloride is added to 100 mL of water. The NaCl completely dissolves. Additional NaCl is added until no more of the solid dissolves. The solution precipitates out the undissolved solid. What is the final type of solution formed?

868. Some sodium bromide is added to 250 mL of water. The NaBr completely dissolves. Additional NaBr is added until no more of the solid dissolves. The solution is separated from the undissolved solid and 250 mL of water is added to the solution. What is the final type of solution formed?

869. You’re given a sodium acetate (NaC2H3O2) solution. A friend drops a small crystal of sodium acetate into the solution, and immediately the solution turns white as a large amount of precipitate forms. What type of solution was the original solution?

870. If you know the molarity of a solution, what additional information is necessary to determine the moles of solute present?

871. If you know the molality of a solution, what additional information is necessary to determine the moles of solute present?

Concentration Calculations

872–880 Calculate the concentration of the solution.

872. A solution contains 1.5 × 10–2 g of lead(II) ions, Pb2+, in 1,275 mL of solution. What is the concentration of lead in parts per thousand (ppt)? Assume the density of the solution is 1.00 g/mL.

873. A solution contains 5.5 × 10–3 g of the pesticide DDT in 2,125 mL of solution. What is the concentration of DDT in parts per million (ppm)? Assume the density of the solution is 1.00 g/mL.

874. A solution contains 8.5 × 10–8 mol of mercury in 1.5 L of solution. What is the concentration of mercury in parts per billion (ppb)? Assume the density of the solution is 1.00 g/mL.

875. A 0.200-mol sample of sodium nitrate, NaNO3, is dissolved in sufficient water to produce 2.5 L of solution. What is the molarity of the solution?

876. A 0.1250-mol sample of sodium hydroxide, NaOH, is dissolved in sufficient water to produce 1,725 mL of solution. What is the molarity of the solution?

877. What is the molarity of a solution formed by dissolving 26 g of NaCl (molar mass = 58 g/mol) in sufficient water to produce 1.5 L of solution?

878. How many moles of lithium chloride, LiCl, are in 3.5 L of a 0.16-M LiCl solution?

879. How many liters of a 0.25-M sulfuric acid (H2SO4) solution are needed to supply 15 g of sulfuric acid? The molar mass of sulfuric acid is 98 g/mol.

880. How many grams of magnesium chloride, MgCl2, are in 1.75 L of a 0.564-M MgCl2 solution? The molar mass of magnesium chloride is 95.2 g/mol.

Dilution

881–888 Answer the dilution problems using M1V1 = M2V2.

881. A student has 1.0 L of 12-M hydrochloric acid, HCl. She wants to dilute the solution to 1.5 M. How many liters of solution can she make?

882. How many liters of 2.0-M sodium hydroxide, NaOH, can you prepare from 0.50 L of 15-M NaOH?

883. What is the molarity of a solution formed by mixing 1.5 L of 6.0-M nitric acid, HNO3, with water to get a final volume of 6.5 L?

884. What is the molarity of a solution formed by adding 15 mL of 6.0-M phosphoric acid, H3PO4, to 135 mL of water?

885. How many liters of a 12-M hydrochloric acid (HCl) solution are necessary to prepare 5.0 L of 1.0-M HCl?

886. How many milliliters of 14-M nitric acid, HNO3, are necessary to prepare 875 mL of 3.0-M nitric acid?

887. Normal saline solution has a sodium chloride (NaCl) concentration of 0.154 M. How many liters of saline solution can you prepare from 1.00 L of 1.00-M NaCl?

888. How many liters of 0.250-M calcium chloride (CaCl2) solution can you prepare from 5.00 L of 1.00-M CaCl2 solution?

Molality

889–894 Do the following molality problems.

889. What is the molality of a solution containing 0.25 mol of potassium bromide, KBr, in 1.25 kg of water?

890. What is the molality of a solution containing 0.014 mol of calcium nitrate, Ca(NO3)2, in 1,775 g of water?

891. What is the molality of a solution containing 10.5 g of hydrogen chloride, HCl, in 0.750 kg of water? The molar mass of HCl is 36.5 g/mol.

892. How many moles of zinc chloride, ZnCl2, are in a 0.16-m solution containing 1.5 kg of water?

893. How many grams of cadmium chloride, CdCl2, are in a 0.015-m cadmium chloride solution if 2.5 kg of solvent is present? The molar mass of cadmium chloride is 183.317 g/mol.

894. A solution of glucose, C6H12O6, was prepared by adding some of this nonelectrolyte to 175 g of water. Based on a freezing point depression experiment, the concentration of the solution was 0.125 m. How many grams of glucose were in the solution? The molar mass of glucose is 180.2 g/mol.

Colligative Properties

895–911 Answer the questions on colligative properties.

895. Calcium nitrate, Ca(NO3)2, is a strong electrolyte. What is the van’t Hoff factor, i, for a calcium nitrate solution?

896. Chloric acid, HClO3, is a strong electrolyte, and chlorous acid, HClO2, is a weak electrolyte. The van’t Hoff factor of a dilute chloric acid solution is 2. How does the van’t Hoff factor of a dilute chlorous acid solution compare?

897. What is the freezing point depression (ΔT) of a 1.50-m solution of sucrose in water? Sucrose is a nonelectrolyte, and the freezing point depression constant of water is 1.86°C/m.

898. What is the freezing point depression (ΔT) of a 12.6-m solution of ethylene glycol ­(antifreeze) in water? Ethylene glycol is a nonelectrolyte, and the freezing point depression constant of water is 1.86°C/m.

899. Isopropyl alcohol, C3H7OH, is a nonelectrolyte. A 0.200-mol sample of isopropyl alcohol is dissolved in 1.00 kg of water. If the boiling point elevation constant (Kb) of water is 0.512°C/m, what is the boiling point elevation (ΔT) of the solution?

900. Propyl alcohol, C3H7OH, is a nonelectrolyte. A 0.370-mol sample of propyl alcohol is dissolved in 1.75 kg of water. If the boiling point elevation constant (Kb) of water is 0.512°C/m, what is the boiling point elevation (ΔT) of the solution?

901. Ethyl alcohol, C2H5OH, is a water-soluble nonelectrolyte. A solution is prepared by adding 17.0 g of ethyl alcohol to 0.750 kg of water. What is the freezing point depression (ΔT) for this solution? The molar mass of ethyl alcohol is 46.1 g/mol, and the freezing point depression constant (Kf) for water is 1.86°C/m.

902. Propylene glycol, C3H6(OH)2, is a water-soluble nonelectrolyte used in some antifreezes. A 125-g sample of propylene glycol is dissolved in 1.25 kg of water. What is the boiling point of the solution? The molar mass of propylene glycol is 76.1 g/mol, and the boiling point elevation constant (Kb) of water is 0.512°C/m.

903. Hydrogen bromide, HBr, is a strong electrolyte in water. What is the boiling point elevation (ΔT) of a solution containing 125 g of HBr in 1.75 kg of water? The molar mass of HBr is 80.9 g/mol, and the boiling point elevation constant (Kb) of water is 0.512°C/m.

904. A 25.0-g sample of methyl alcohol, CH3OH, is dissolved in 1.50 kg of water. What is the freezing point of the solution? The molar mass of methyl alcohol (a nonelectrolyte) is 32.0 g/mol, and the freezing point depression constant (Kf) for water is 1.86°C/m.

905. Rubidium chloride, RbCl, is a strong electrolyte. What is the freezing point of a solution formed by dissolving 15.0 g of RbCl in 0.125 kg of water? The molar mass of RbCl is 121 g/mol, and the freezing point depression constant (Kf) for water is 1.86°C/m.

906. Hexane, C6H14, is a nonelectrolyte. A solution contains 125 g of hexane in 1.50 kg of cyclohexane, C6H12. What is the boiling point of the solution? The molar mass of hexane is 86.2 g/mol, and the boiling point elevation constant (Kb) of cyclohexane is 2.79°C/m. The normal boiling point of cyclohexane is 80.70°C.

907. What is the osmotic pressure (Π) of a solution containing 0.125 mol of a nonelectrolyte in 0.500 L of solution at 25°C? R = 0.0821 L·atm/mol·K.

908. What is the osmotic pressure (Π) of a 1.25-M solution of a nonelectrolyte solution at 25°C? R = 0.0821 L·atm/mol·K.

909. Unlike many metallic compounds, mercury(II) chloride, HgCl2, is a nonelectrolyte. What is the osmotic pressure (Π) of a solution containing 5.00 g of mercury(II) chloride in 0.275 L of solution at 45°C? The molar mass of mercury(II) chloride is 272 g/mol, and R = 0.0821 L·atm/mol·K.

910. An aqueous solution of a polymer contains 0.410 g of this compound in 1.00 L of solution. At 37°C, the osmotic pressure (Π) of the solution is 3.00 × 10–3 atm. What is the molar mass of the polymer? R = 0.0821 L·atm/mol·K.

911. Calcium nitrate, Ca(NO3)2, is a strong electrolyte. A solution contains 4.75 g of calcium nitrate in 125 mL of solution. What is the osmotic pressure (Π) of this solution at 37°C? The molar mass of calcium nitrate is 164 g/mol, and R = 0.0821 L·atm/mol·K.