Q: Which of the following correctly defines molarity ($M$) for a solution?

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

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

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

Q: How would you calculate the concentration in parts per million (ppm)?

$\text{ppm} = \text{parts by mass} \times 10^6$

Q: Which of the following best describes molality ($m$)?

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

Q: Which of the following is the correct formula for mole fraction ($X$) of a solute?

$X = \frac{\text{amount (mol) of solute}}{\text{amount (mol) of solute} + \text{amount (mol) of solvent}}$

Question 1

Which of the following correctly defines molarity ($M$) for a solution?

Accepted Answer

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

Question 2

A laboratory technician dissolves 1.25 g of calcium chloride ($	ext{CaCl}_2$) in 50.0 mL of water. What is the molarity of the solution? (Molar mass of $	ext{CaCl}_2 = 110.98$ g/mol)

Accepted Answer

$0.225\ M$

Question 3

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

Accepted Answer

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

Question 4

A solution contains 5.00 g of sodium acetate in 100.0 g of water. What is the mass percent of sodium acetate in the solution?

Accepted Answer

$4.76\%$

Question 5

How would you calculate the concentration in parts per million (ppm)?

Accepted Answer

$	ext{ppm} = 	ext{parts by mass} 	imes 10^6$

Question 6

A water sample contains $0.0025$ mol of mercury ($	ext{Hg}$) in $10,000$ L of water. What is the concentration in ppm and ppb? (Molar mass of Hg = 200.59 g/mol; 1 L water = 1 kg)

Accepted Answer

$0.050$ ppm and $50$ ppb

Question 7

Which of the following best describes molality ($m$)?

Accepted Answer

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

Question 8

Calculate the molality of a solution made by dissolving 1.25 g of potassium nitrate ($	ext{KNO}_3$) in 25.0 mL of water. (Density of water = 1 g/mL, Molar mass of $	ext{KNO}_3 = 101.1$ g/mol)

Accepted Answer

$0.495\ m$

Question 9

A solution is prepared by mixing 80.0 g of isopropyl alcohol (density = 0.786 g/mL) and 20.0 g of water (density = 1 g/mL). What is the volume percent of isopropyl alcohol in the solution?

Accepted Answer

$83.6\%$

Question 10

Which of the following is the correct formula for mole fraction ($X$) of a solute?

Accepted Answer

$X = \frac{	ext{amount (mol) of solute}}{	ext{amount (mol) of solute} + 	ext{amount (mol) of solvent}}$

Question 11

What is the mole fraction of iron (III) chloride when 10.5 g of $	ext{FeCl}_3$ is dissolved in 250.0 g of water? (Molar mass of $	ext{FeCl}_3 = 162.2$ g/mol, Molar mass of $	ext{H}_2	ext{O} = 18.0$ g/mol)

Accepted Answer

$0.00464$

Question 12

Which concentration unit is most appropriate for expressing the amount of a toxic pollutant in drinking water at very low concentrations?

Accepted Answer

Parts per billion (ppb)

Question 13

A chemist needs to prepare 250 mL of a 0.100 M NaCl solution. How many grams of NaCl (molar mass = 58.44 g/mol) are required?

Accepted Answer

$1.46$ g

Question 14

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 15

A solution is labeled as 12% (v/v) ethanol. What does this mean?

Accepted Answer

There are 12 mL of ethanol in every 100 mL of solution.

Question 16

Which of the following would NOT change the molality of a solution?

Accepted Answer

Heating the solution (assuming no evaporation)

Question 17

A solution contains 0.10 mol of glucose and 0.90 mol of water. What is the mole percent of glucose?

Accepted Answer

$10\%$

Question 18

Which of the following is a real-world application where mass percent is commonly used?

Accepted Answer

Determining the sugar content in soft drinks

Solution Concentration: Definitions, Calculations, and Applications

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