Q: Which of the following correctly defines molality ($$m) of a $$solution?

$$m = \frac{\text{amount of solute (mol)}}{\text{mass of solvent (kg)}}$$

Q: A laboratory technician needs to prepare 500.0 mL of 0.250 M NaCl solution. What mass of NaCl (molar mass = 58.44 g/mol) should be weighed out?

$$0.250 \text{ mol/L} \times 0.500 \text{ L} \times 58.44 \text{ g/mol} = 7.305 \text{ g}$$

Q: A solution is made by dissolving 8.60 g of glucose (molar mass = 180.02 g/mol) in 26.5 g of water. What is the mole fraction of glucose in the solution?

$$X_{\text{glucose}} = \frac{0.0477}{1.4705 + 0.0477} = 0.0314$$

Q: A 30.0% by mass solution of hydrogen peroxide ($$\mathrm{H_2O_2}) $$has a density of 1.135 g/mL. What is the molality of this solution? (Molar mass $$\mathrm{H_2O_2} = 34.02 g/$$mol)

$$m = \frac{8.82 \text{ mol}}{0.700 \text{ kg}} = 12.6 \ m$$

Q: A 15.68 mL sample of drinking water contains 0.01800 $$\mug of $$lead. What is the concentration of lead in parts per billion (ppb)? (Density of water = 1.00 g/mL)

$$\text{ppb} = \frac{0.01800 \times 10$$^{-6}$$ \text{ g}}{15.68 \text{ g}} \times 10^9$ = 1.148$$

Q: Which of the following is the correct formula for calculating mass percent of a solute in a solution?

$$\text{mass} \% = \frac{\text{mass of solute}}{\text{mass of solution}} \times 100$$

Q: A 10.40 mL sample of lake water contains 20.60 $$\mug of $$copper. What is the concentration of copper in parts per million (ppm)? (Density of water = 1.00 g/mL)

$$\text{ppm} = \frac{20.60 \times 10$$^{-6}$$ \text{ g}}{10.40 \text{ g}} \times 10^6$ = 1.981$$

Question 1

Which of the following correctly defines molality ($$m) of a $$solution?

Accepted Answer

$$m = \frac{	ext{amount of solute (mol)}}{	ext{mass of solvent (kg)}}$$

Question 2

A laboratory technician needs to prepare 500.0 mL of 0.250 M NaCl solution. What mass of NaCl (molar mass = 58.44 g/mol) should be weighed out?

Accepted Answer

$$0.250 	ext{ mol/L} 	imes 0.500 	ext{ L} 	imes 58.44 	ext{ g/mol} = 7.305 	ext{ g}$$

Question 3

Which of the following statements about molarity and molality is correct?

Accepted Answer

Molarity depends on the volume of solution, while molality depends on the mass of solvent.

Question 4

A 10.0% (m/v) NaCl solution is prepared. Which of the following best describes this solution?

Accepted Answer

10.0 g NaCl is dissolved in enough water to make 100 mL of solution.

Question 5

A solution is made by dissolving 8.60 g of glucose (molar mass = 180.02 g/mol) in 26.5 g of water. What is the mole fraction of glucose in the solution?

Accepted Answer

$$X_{	ext{glucose}} = \frac{0.0477}{1.4705 + 0.0477} = 0.0314$$

Question 6

A 30.0% by mass solution of hydrogen peroxide ($$\mathrm{H_2O_2}) $$has a density of 1.135 g/mL. What is the molality of this solution? (Molar mass $$\mathrm{H_2O_2} = 34.02 g/$$mol)

Accepted Answer

$$m = \frac{8.82 	ext{ mol}}{0.700 	ext{ kg}} = 12.6 \ m$$

Question 7

Which of the following best describes how to prepare 2.00 L of 0.968 M HCl solution from 12.1 M concentrated HCl?

Accepted Answer

Dilute 0.160 L (160 mL) of concentrated HCl to a final volume of 2.00 L with water.

Question 8

A 15.68 mL sample of drinking water contains 0.01800 $$\mug of $$lead. What is the concentration of lead in parts per billion (ppb)? (Density of water = 1.00 g/mL)

Accepted Answer

$$	ext{ppb} = \frac{0.01800 	imes 10$$^{-6}$$ 	ext{ g}}{15.68 	ext{ g}} 	imes 10^9$ = 1.148$$

Question 9

Which of the following is the correct formula for calculating mass percent of a solute in a solution?

Accepted Answer

$$	ext{mass} \% = \frac{	ext{mass of solute}}{	ext{mass of solution}} 	imes 100$$

Question 10

A 10.40 mL sample of lake water contains 20.60 $$\mug of $$copper. What is the concentration of copper in parts per million (ppm)? (Density of water = 1.00 g/mL)

Accepted Answer

$$	ext{ppm} = \frac{20.60 	imes 10$$^{-6}$$ 	ext{ g}}{10.40 	ext{ g}} 	imes 10^6$ = 1.981$$

Question 11

Which of the following is true regarding the preparation of a solution by dilution?

Accepted Answer

The number of moles of solute before and after dilution remains the same.

Question 12

A 30.0% by mass solution of hydrogen peroxide ($$\mathrm{H_2O_2}) $$has a density of 1.135 g/mL. What is the molarity of this solution? (Molar mass $$\mathrm{H_2O_2} = 34.02 g/$$mol)

Accepted Answer

$$M = \frac{8.82 	ext{ mol}}{0.881 	ext{ L}} = 10.0 	ext{ M}$$

Question 13

Which of the following best describes a 10% (v/v) aqueous solution of methanol?

Accepted Answer

10 mL of methanol is diluted with water to a final volume of 100 mL.

Question 14

A solution contains 23.40 g of naphthalene ($$\mathrm{C$$_{10}$$H_8$$}$$) dissolved in 99.60 g of benzene ($$\mathrm{C_6H_6}$). What is the mass percent of naphthalene in the solution?

Accepted Answer

$$	ext{mass} \% = \frac{23.40}{23.40 + 99.60} 	imes 100 = 19.02\%$$

Question 15

A 11.76 mL sample of drinking water contains 0.000400 $$\mug of $$lead. What is the concentration of lead in parts per trillion (ppt)? (Density of water = 1.00 g/mL)

Accepted Answer

$$	ext{ppt} = \frac{0.000400 	imes 10$$^{-6}$$ 	ext{ g}}{11.76 	ext{ g}} 	imes 10$$^{12}$$ = 34.0$$

Question 16

Which of the following is the correct formula for calculating mole fraction ($$X_A) of $$component A in a solution?

Accepted Answer

$$X_A = \frac{n_A}{n_{	ext{total}}}$$

Question 17

A natural water sample contains $$8.90 	imes 10$$^{-9}$$ M of $$\mathrm{$$C_{21}H$$_{44}}$$ (molar mass = 296.5 g/mol). What is the concentration in ppb? (Assume density of water is 1.00 g/mL)

Accepted Answer

$$	ext{ppb} = \frac{2.64 	imes 10$$^{-6}$$ 	ext{ g}}{1 	ext{ kg}} 	imes 10^9$ = 2.64$$

Question 18

Which of the following statements about parts per million (ppm), parts per billion (ppb), and parts per trillion (ppt) is correct for dilute aqueous solutions?

Accepted Answer

1 ppm = 1 mg solute per 1 L solution; 1 ppb = 1 $$\mug $$solute per 1 L solution; 1 ppt = 1 ng solute per 1 L solution.

Chapter 14 lecture 2

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