Q: A solution is prepared by dissolving 15 g of salt in 60 g of water. What is the mass-mass percentage concentration of the solution?

$$\frac{15}{15+60} \times 100 = 20\%$$

Q: A solution contains 478 mg and is 12.5% mass-mass. How many grams of solute are present?

$$\frac{12.5}{100} \times 478\ \text{mg} = 59.75\ \text{mg} = 0.0598\ \text{g}$$

Q: A 320 ml alcoholic solution at 20% v/v is diluted by adding 80 ml of water. What is the new v/v concentration?

$$\frac{0.2 \times 320}{320+80} \times 100 = 16\%$$

Q: A bottle of wine contains 0.750 L and is labeled as 11.5% alcohol by volume. How many liters of alcohol are present?

$$0.750 \times 0.115 = 0.08625\ \text{L}$$

Q: If potable water should contain 1.6 ppm of fluoride ($$F^-) to $$prevent dental caries, how many grams of fluoride are in $$1 \times 10^6$ kg of water?

$$1.6\ \text{mg/L} \times 1 \times 10^6$\ \text{kg} = 1.6\ \text{kg} = 1600\ \text{g}$$

Q: A solution contains 1 ppm of solute. Express this concentration in $$\mug/L$$, mg/L, and g/L.

$$1\ \text{ppm} = 1\ \text{mg/L} = 1000\ \mu\text{g/L} = 0.001\ \text{g/L}$$

Q: Calculate the molarity and normality of a solution prepared by dissolving 2 g of potassium chlorate ($$KClO_3) in $$enough water to make 150 ml of solution. (Molar mass $$KClO_3 = 122.55$ g/mol)

Molarity: $$\frac{2}{122.55 \times 0.150} = 0.109\ \text{M}$$; Normality: $$0.109 \times 1 = 0.109\ \text{N}$$

Q: A solution of nitric acid ($$HNO_3) $$has 35% by mass and a density of 1.21 g/ml. What is the molarity of $$HNO_3$$? (Molar mass $$HNO_3 = 63$ g/mol)

Molarity: $$\frac{1.21 \times 0.35}{63} \times 1000 = 6.73\ \text{M}$$

Q: A solution contains 63.3 ppm of $$K_3$$[Fe(CN)_6]$$. What is the molarity of K$$^+$$ ions? (Molar mass K_3$[Fe(CN)_6] = 329 g/$$mol)

Molarity: $$\frac{63.3 \times 10$$^{-3}$$}{329} \times 3 = 5.77 \times 10$$^{-4}$$\ \text{M}$$

Q: A sample of seawater with density 1.02 g/ml contains 17.8 ppm of nitrate ($$NO_3$$^-$$). What is the molarity of nitrate in the water? (Molar mass NO_3$^- = 62 g/$$mol)

Molarity: $$\frac{17.8 \times 10$$^{-3}$$}{62} = 2.87 \times 10$$^{-4}$$\ \text{M}$$

Question 1

A solution is prepared by dissolving 15 g of salt in 60 g of water. What is the mass-mass percentage concentration of the solution?

Accepted Answer

$$\frac{15}{15+60} 	imes 100 = 20\%$$

Question 2

How many grams of solute and solvent are needed to prepare 400 g of a solution at 25% mass-mass concentration?

Accepted Answer

100 g solute, 300 g solvent

Question 3

A solution contains 478 mg and is 12.5% mass-mass. How many grams of solute are present?

Accepted Answer

$$\frac{12.5}{100} 	imes 478\ 	ext{mg} = 59.75\ 	ext{mg} = 0.0598\ 	ext{g}$$

Question 4

A 320 ml alcoholic solution at 20% v/v is diluted by adding 80 ml of water. What is the new v/v concentration?

Accepted Answer

$$\frac{0.2 	imes 320}{320+80} 	imes 100 = 16\%$$

Question 5

A bottle of wine contains 0.750 L and is labeled as 11.5% alcohol by volume. How many liters of alcohol are present?

Accepted Answer

$$0.750 	imes 0.115 = 0.08625\ 	ext{L}$$

Question 6

If potable water should contain 1.6 ppm of fluoride ($$F^-) to $$prevent dental caries, how many grams of fluoride are in $$1 	imes 10^6$ kg of water?

Accepted Answer

$$1.6\ 	ext{mg/L} 	imes 1 	imes 10^6$\ 	ext{kg} = 1.6\ 	ext{kg} = 1600\ 	ext{g}$$

Question 7

A solution contains 1 ppm of solute. Express this concentration in $$\mug/L$$, mg/L, and g/L.

Accepted Answer

$$1\ 	ext{ppm} = 1\ 	ext{mg/L} = 1000\ \mu	ext{g/L} = 0.001\ 	ext{g/L}$$

Question 8

Calculate the molarity and normality of a solution prepared by dissolving 2 g of potassium chlorate ($$KClO_3) in $$enough water to make 150 ml of solution. (Molar mass $$KClO_3 = 122.55$ g/mol)

Accepted Answer

Molarity: $$\frac{2}{122.55 	imes 0.150} = 0.109\ 	ext{M}$$; Normality: $$0.109 	imes 1 = 0.109\ 	ext{N}$$

Question 9

A solution of nitric acid ($$HNO_3) $$has 35% by mass and a density of 1.21 g/ml. What is the molarity of $$HNO_3$$? (Molar mass $$HNO_3 = 63$ g/mol)

Accepted Answer

Molarity: $$\frac{1.21 	imes 0.35}{63} 	imes 1000 = 6.73\ 	ext{M}$$

Question 10

A solution contains 63.3 ppm of $$K_3$$[Fe(CN)_6]$$. What is the molarity of K$$^+$$ ions? (Molar mass K_3$[Fe(CN)_6] = 329 g/$$mol)

Accepted Answer

Molarity: $$\frac{63.3 	imes 10$$^{-3}$$}{329} 	imes 3 = 5.77 	imes 10$$^{-4}$$\ 	ext{M}$$

Question 11

A sample of seawater with density 1.02 g/ml contains 17.8 ppm of nitrate ($$NO_3$$^-$$). What is the molarity of nitrate in the water? (Molar mass NO_3$^- = 62 g/$$mol)

Accepted Answer

Molarity: $$\frac{17.8 	imes 10$$^{-3}$$}{62} = 2.87 	imes 10$$^{-4}$$\ 	ext{M}$$

Question 12

2.28 g of $$Al_2$$($$SO_4)_3$ are dissolved to make 200 ml of solution. Calculate the molarity and normality. (Molar mass Al_2$(SO_4$)_3 = 342 g/$$mol)

Accepted Answer

Molarity: $$\frac{2.28}{342 	imes 0.2} = 0.0334\ 	ext{M}$$; Normality: $$0.0334 	imes 6 = 0.200\ 	ext{N}$$

Question 13

A solution is prepared by dissolving 1.2 g of methanol ($$CH_3OH) in 16.8 g of $$water. What is the mole fraction of methanol in the solution? (Molar mass $$CH_3OH = 32 g/$$mol, $$H_2O = 18 g/$$mol)

Accepted Answer

Mole fraction: $$\frac{1.2/32}{1.2/32 + 16.8/18} = 0.0406$$

Question 14

You need to prepare 500 ml of acetic acid solution at 1 M from a concentrated solution of 17.5 M. What volume of the concentrated solution is required?

Accepted Answer

$$V_1$$ = \frac{$$C_2$$ $$V_2$$}{$$C_1$$} = \frac{1 	imes 500}{17.5} = 28.6\ 	ext{ml}$$

Question 15

How many ml of HCl solution (density 1.19 g/ml, 37% by mass) are needed to prepare 250 ml of 1 M HCl?

Accepted Answer

$$	ext{Required mass} = 1 	imes 0.25 	imes 36.46 = 9.115\ 	ext{g}$$; $$	ext{Volume} = \frac{9.115}{1.19 	imes 0.37} = 20.1\ 	ext{ml}$$

Question 16

A solution is made by mixing 250 ml of $$H_2SO_4 0.1 M$$, 20 ml of $$H_2SO_4 0.2 M$$, and 100 ml of $$H_2SO_4 0.15 M. $$What is the molarity of the resulting solution?

Accepted Answer

$$\frac{(250 	imes 0.1) + (20 	imes 0.2) + (100 	imes 0.15)}{250+20+100} = 0.116\ 	ext{M}$$

Question 17

A pharmacy sells hydrogen peroxide solutions at 3% by mass. According to the reaction $$2H_2O_2 \rightarrow 2H_2O + O_2$, what mass of solution is needed to produce 1 g of O_2$?

Accepted Answer

$$	ext{Moles of } O_2$ = \frac{1}{32} = 0.03125$$; $$	ext{Moles of } H_2O_2 = 2 	imes 0.03125 = 0.0625$$; $$	ext{Mass of } H_2O_2 = 0.0625 	imes 34 = 2.125$$; $$	ext{Mass of solution} = \frac{2.125}{0.03} = 70.8\ 	ext{g}$$

Question 18

How many ml of 0.125 M NaOH are needed to completely react with 15 ml of 0.118 M $$H_2SO_4$$? (Reaction: $$2NaOH + H_2SO_4 \rightarrow Na_2SO_4 + 2H_2O)$$

Accepted Answer

$$	ext{Moles of } H_2SO_4 = 0.015 	imes 0.118 = 0.00177$$; $$	ext{Moles of NaOH} = 2 	imes 0.00177 = 0.00354$$; $$	ext{Volume} = \frac{0.00354}{0.125} = 0.0283\ 	ext{L} = 28.3\ 	ext{ml}$$

Question 19

A tablet contains 2 g of $$Ca(OH)_2. $$How many ml of 0.100 M HCl can it neutralize? (Reaction: $$Ca(OH)_2 + 2HCl \rightarrow $$CaCl_2$$ + 2H_2O)$$

Accepted Answer

$$	ext{Moles of } Ca(OH)_2 = \frac{2}{74} = 0.0270$$; $$	ext{Moles of HCl} = 2 	imes 0.0270 = 0.0540$$; $$	ext{Volume} = \frac{0.0540}{0.100} = 0.540\ 	ext{L} = 540\ 	ext{ml}$$

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