Q: A sample of tap water contains 0.0537 g of NaCl in 250.0 g of solution. What is the concentration in ppm?

$$\text{ppm} = \frac{0.0537 \times 1000}{0.250} = 215\ ppm$$

Q: Which formula correctly calculates the molar concentration ($$mol\ L$$^{-1}$$) of a solution?

$$c = \frac{\text{amount of solute (mol)}}{\text{volume of solution (L)}}$$

Q: A saturated solution of calcium carbonate contains 0.198 g of solute in 200 mL of solution. What is the concentration in ppm?

$$\text{ppm} = \frac{198}{0.200} = 990\ ppm$$

Q: If a solution contains 168 mg of silver nitrate ($$AgNO_3) $$dissolved in 150 mL of solution, what is its molar concentration? (Molar mass of $$AgNO_3 = 169.9$$\ g\ $$mol^{-1})$$

$$c = \frac{0.168/169.9}{0.150} = 6.59 \times 10$$^{-3}$$\ mol\ L$$^{-1}$$

Question 1

Which of the following best describes a concentrated solution?

Accepted Answer

A solution with a high ratio of solute to solvent.

Question 2

What is the concentration in $$g\ L$$^{-1}$$ of a solution containing 5.00 g of glucose dissolved in 250 mL of water?

Accepted Answer

$$c = \frac{5.00}{0.250} = 20.0\ g\ L$$^{-1}$$

Question 3

A sample of tap water contains 0.0537 g of NaCl in 250.0 g of solution. What is the concentration in ppm?

Accepted Answer

$$	ext{ppm} = \frac{0.0537 	imes 1000}{0.250} = 215\ ppm$$

Question 4

Which formula correctly calculates the molar concentration ($$mol\ L$$^{-1}$$) of a solution?

Accepted Answer

$$c = \frac{	ext{amount of solute (mol)}}{	ext{volume of solution (L)}}$$

Question 5

A solution contains 0.24 mol of glucose dissolved in 500 mL of water. What is its molar concentration?

Accepted Answer

$$c = \frac{0.24}{0.500} = 0.48\ mol\ L$$^{-1}$$

Question 6

A saturated solution of calcium carbonate contains 0.198 g of solute in 200 mL of solution. What is the concentration in ppm?

Accepted Answer

$$	ext{ppm} = \frac{198}{0.200} = 990\ ppm$$

Question 7

Which of the following is a correct definition of 'parts per million' (ppm)?

Accepted Answer

The mass of solute (in mg) per mass of solution (in kg).

Question 8

A solution contains 0.105 mol of potassium nitrate ($$KNO_3) $$dissolved in 200 mL of solution. What is its molar concentration?

Accepted Answer

$$c = \frac{0.105}{0.200} = 0.525\ mol\ L$$^{-1}$$

Question 9

If a solution contains 168 mg of silver nitrate ($$AgNO_3) $$dissolved in 150 mL of solution, what is its molar concentration? (Molar mass of $$AgNO_3 = 169.9$$\ g\ $$mol^{-1})$$

Accepted Answer

$$c = \frac{0.168/169.9}{0.150} = 6.59 	imes 10$$^{-3}$$\ mol\ L$$^{-1}$$

Question 10

A solution contains 4.00 g of ethanoic acid ($$CH_3COOH) $$dissolved in 100 mL of solution. What is its molar concentration? (Molar mass of $$CH_3COOH = 60.05\ g\ $$mol^{-1}$$)

Accepted Answer

$$c = \frac{4.00/60.05}{0.100} = 0.666\ mol\ L$$^{-1}$$

Question 11

Which of the following would be considered a dilute solution?

Accepted Answer

A solution with a low ratio of solute to solvent.

Question 12

A chemist needs to prepare 1 L of a 0.5 $$mol\ L$$^{-1}$$ NaCl solution. How many grams of NaCl (molar mass = 58.44 g$$\ $$mol^{-1}) $$are required?

Accepted Answer

$$0.5 	imes 58.44 = 29.22\ g$$

Question 13

A water sample contains 0.0025 g of lead in 2.0 kg of water. What is the concentration in ppm?

Accepted Answer

$$	ext{ppm} = \frac{2.5}{2.0} = 1.25\ ppm$$

Question 14

Which of the following is NOT a correct unit for expressing concentration?

Accepted Answer

$$kg\ $$mol^{-1}$$

Question 15

A solution contains 25.0 mL of 0.3277 $$mol\ L$$^{-1}$$ ammonia (NH_3$). How many moles of ammonia are present?

Accepted Answer

$$n = 0.3277 	imes 0.0250 = 8.19 	imes 10$$^{-3}$$\ mol$$

Question 16

Why is ppm commonly used for measuring contaminants in water?

Accepted Answer

Because contaminants are often present in very small amounts.

Question 17

A fish sample contains 0.005 mg of mercury in 5 g of tissue. What is the concentration in ppm?

Accepted Answer

Question 18

Which step is necessary before calculating concentration in $$g\ L$$^{-1}$$ if the volume is given in mL?

Accepted Answer

Convert the volume from mL to L by dividing by 1000.

Concentration of Solutions: Methods and Calculations

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