Concentration Terms for Competitive Exam Success

Concentration Terms

Q. A solution contains 20% (w/w) of glucose. If the total mass of the solution is 200 g, what is the mass of glucose in the solution?

A. 20 g
B. 40 g
C. 60 g
D. 80 g

Solution

Mass of glucose = (20/100) x 200 g = 40 g.

Correct Answer: B — 40 g

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Q. A solution has a concentration of 0.1 M NaCl. How many grams of NaCl are present in 1 liter of this solution? (Molar mass of NaCl = 58.5 g/mol)

A. 5.85 g
B. 58.5 g
C. 0.1 g
D. 0.585 g

Solution

Mass = moles x molar mass = 0.1 moles x 58.5 g/mol = 5.85 g.

Correct Answer: B — 58.5 g

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Q. A solution has a concentration of 0.2 M. How many moles of solute are present in 1.5 L of this solution?

A. 0.3 moles
B. 0.5 moles
C. 0.2 moles
D. 0.15 moles

Solution

Moles of solute = Molarity × Volume = 0.2 M × 1.5 L = 0.3 moles.

Correct Answer: B — 0.5 moles

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Q. A solution has a density of 1.2 g/mL and contains 10% (w/v) NaCl. What is the mass of NaCl in 1 liter of this solution?

A. 100 g
B. 120 g
C. 80 g
D. 60 g

Solution

Mass of NaCl = (10/100) x 1000 mL = 100 g.

Correct Answer: B — 120 g

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Q. A solution has a density of 1.2 g/mL and contains 10% (w/v) NaOH. What is the mass of NaOH in 1 L of this solution?

A. 100 g
B. 120 g
C. 80 g
D. 60 g

Solution

Mass of NaOH = (10/100) x 1000 mL = 100 g.

Correct Answer: B — 120 g

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Q. A solution has a density of 1.2 g/mL and contains 30 g of solute. What is the molarity if the molar mass of the solute is 60 g/mol?

A. 0.5 M
B. 1 M
C. 2 M
D. 1.5 M

Solution

Volume of solution = mass / density = 30 g / 1.2 g/mL = 25 mL = 0.025 L. Moles of solute = 30 g / 60 g/mol = 0.5 moles. Molarity = 0.5 moles / 0.025 L = 20 M.

Correct Answer: B — 1 M

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Q. A solution is prepared by dissolving 50 g of glucose (C6H12O6) in 250 g of water. What is the mass percent of glucose in the solution? (Molar mass of glucose = 180 g/mol)

A. 20%
B. 15%
C. 25%
D. 10%

Solution

Mass percent = (mass of solute / (mass of solute + mass of solvent)) × 100 = (50 g / (50 g + 250 g)) × 100 = 20%.

Correct Answer: A — 20%

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Q. A solution is prepared by dissolving 58.5 g of NaCl in 1 L of water. What is the concentration in terms of molarity? (Molar mass of NaCl = 58.5 g/mol)

A. 1 M
B. 2 M
C. 0.5 M
D. 0.25 M

Solution

Moles of NaCl = 58.5 g / 58.5 g/mol = 1 mole. Molarity = 1 mole / 1 L = 1 M.

Correct Answer: A — 1 M

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Q. A solution is prepared by dissolving 58.5 g of NaCl in 1 L of water. What is the molarity of the solution? (Molar mass of NaCl = 58.5 g/mol)

A. 1 M
B. 2 M
C. 0.5 M
D. 0.1 M

Solution

Moles of NaCl = 58.5 g / 58.5 g/mol = 1 mole. Molarity = moles of solute / liters of solution = 1 mole / 1 L = 1 M.

Correct Answer: A — 1 M

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Q. A solution is prepared by dissolving 58.5 g of NaCl in enough water to make 1 L of solution. What is the molarity of the solution? (Molar mass of NaCl = 58.5 g/mol)

A. 1 M
B. 2 M
C. 0.5 M
D. 0.1 M

Solution

Moles of NaCl = 58.5 g / 58.5 g/mol = 1 mole. Molarity = 1 mole / 1 L = 1 M.

Correct Answer: A — 1 M

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Q. How many grams of solute are needed to prepare 0.5 L of a 1 M NaCl solution? (Molar mass of NaCl = 58.5 g/mol)

A. 29.25 g
B. 58.5 g
C. 14.625 g
D. 0.5 g

Solution

Mass of solute = moles × molar mass = 1 mol × 58.5 g/mol = 58.5 g. For 0.5 L, it is 0.5 mol × 58.5 g/mol = 29.25 g.

Correct Answer: A — 29.25 g

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Q. How many grams of solute are needed to prepare 2 L of a 1 M solution? (Molar mass = 58.5 g/mol)

A. 58.5 g
B. 117 g
C. 29.25 g
D. 145 g

Solution

Grams of solute = moles x molar mass = 2 moles x 58.5 g/mol = 117 g.

Correct Answer: B — 117 g

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Q. If 1 L of a 2 M solution is diluted to 3 L, what is the new molarity of the solution?

A. 0.67 M
B. 1 M
C. 1.5 M
D. 2 M

Solution

Using the dilution formula M1V1 = M2V2, we have 2 M * 1 L = M2 * 3 L, thus M2 = 2/3 = 0.67 M.

Correct Answer: A — 0.67 M

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Q. If 1 L of a 3 M solution is diluted to 2 L, what is the new molarity?

A. 1.5 M
B. 3 M
C. 6 M
D. 0.5 M

Solution

Using the dilution formula M1V1 = M2V2, we have 3 M × 1 L = M2 × 2 L. Thus, M2 = 1.5 M.

Correct Answer: A — 1.5 M

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Q. If 1 liter of a 2 M solution is diluted to 3 liters, what is the new molarity?

A. 0.67 M
B. 1 M
C. 1.5 M
D. 2 M

Solution

Using the dilution formula M1V1 = M2V2, (2 M)(1 L) = M2(3 L) => M2 = 2/3 = 0.67 M.

Correct Answer: A — 0.67 M

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Q. If 1 mole of solute is dissolved in 1 liter of solution, what is the concentration in terms of molarity?

A. 1 M
B. 2 M
C. 0.5 M
D. 0.25 M

Solution

Molarity (M) = moles of solute / liters of solution = 1 mole / 1 L = 1 M.

Correct Answer: A — 1 M

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Q. If 10 grams of NaCl is dissolved in 500 mL of water, what is the mass/volume percent concentration?

A. 1%
B. 2%
C. 5%
D. 10%

Solution

Mass/volume percent = (mass of solute / volume of solution) x 100 = (10 g / 500 mL) x 100 = 2%.

Correct Answer: B — 2%

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Q. If 10 grams of NaCl is dissolved in 500 mL of water, what is the molality of the solution? (Molar mass of NaCl = 58.5 g/mol)

A. 0.34 m
B. 0.17 m
C. 0.85 m
D. 0.50 m

Solution

Molality (m) = moles of solute / kg of solvent. Moles of NaCl = 10 g / 58.5 g/mol = 0.171 moles. Mass of water = 0.5 kg. Molality = 0.171 moles / 0.5 kg = 0.342 m.

Correct Answer: A — 0.34 m

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Q. If 10 grams of NaCl is dissolved in enough water to make 500 mL of solution, what is the molality of the solution? (Molar mass of NaCl = 58.5 g/mol)

A. 0.34 m
B. 0.17 m
C. 0.85 m
D. 0.50 m

Solution

Moles of NaCl = 10 g / 58.5 g/mol = 0.171 moles. Mass of solvent (water) = 0.5 kg. Molality (m) = moles of solute / kg of solvent = 0.171 moles / 0.5 kg = 0.34 m.

Correct Answer: A — 0.34 m

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Q. If 10 grams of NaOH is dissolved in 500 mL of solution, what is the molality of the solution? (Molar mass of NaOH = 40 g/mol)

A. 0.5 m
B. 1 m
C. 2 m
D. 0.25 m

Solution

Moles of NaOH = 10 g / 40 g/mol = 0.25 moles. Mass of solvent (water) = 0.5 kg. Molality (m) = moles of solute / kg of solvent = 0.25 moles / 0.5 kg = 0.5 m.

Correct Answer: B — 1 m

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Q. If 10 grams of NaOH is dissolved in enough water to make 500 mL of solution, what is the molarity of the solution? (Molar mass of NaOH = 40 g/mol)

A. 0.5 M
B. 1 M
C. 2 M
D. 0.25 M

Solution

Moles of NaOH = 10 g / 40 g/mol = 0.25 moles. Molarity = 0.25 moles / 0.5 L = 0.5 M.

Correct Answer: B — 1 M

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Q. If 100 g of glucose (C6H12O6) is dissolved in 1 L of solution, what is the molarity of the solution? (Molar mass of glucose = 180 g/mol)

A. 0.56 M
B. 1.0 M
C. 0.33 M
D. 0.75 M

Solution

Moles of glucose = 100 g / 180 g/mol = 0.556 moles. Molarity = moles of solute / liters of solution = 0.556 moles / 1 L = 0.56 M.

Correct Answer: A — 0.56 M

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Q. If 15 grams of HCl is dissolved in 500 mL of solution, what is the molarity of the solution? (Molar mass of HCl = 36.5 g/mol)

A. 0.82 M
B. 1.0 M
C. 0.5 M
D. 1.5 M

Solution

Moles of HCl = 15 g / 36.5 g/mol = 0.41096 moles. Molarity = 0.41096 moles / 0.5 L = 0.82192 M.

Correct Answer: A — 0.82 M

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Q. If 15 grams of sugar is dissolved in 250 mL of solution, what is the molarity of the solution? (Molar mass of sugar = 180 g/mol)

A. 0.33 M
B. 0.5 M
C. 0.25 M
D. 0.75 M

Solution

Moles of sugar = 15 g / 180 g/mol = 0.0833 moles. Molarity = 0.0833 moles / 0.25 L = 0.333 M.

Correct Answer: A — 0.33 M

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Q. If 15 grams of sugar is dissolved in 250 mL of water, what is the molarity of the solution? (Molar mass of sugar = 180 g/mol)

A. 0.33 M
B. 0.5 M
C. 0.25 M
D. 0.75 M

Solution

Moles of sugar = 15 g / 180 g/mol = 0.0833 moles. Molarity = 0.0833 moles / 0.25 L = 0.333 M.

Correct Answer: A — 0.33 M

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Q. If 2 moles of glucose are dissolved in 1 liter of water, what is the molarity of the solution?

A. 1 M
B. 2 M
C. 0.5 M
D. 3 M

Solution

Molarity = moles of solute / liters of solution = 2 moles / 1 L = 2 M.

Correct Answer: B — 2 M

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Q. If 2 moles of KCl are dissolved in 1 liter of solution, what is the molarity of the solution?

A. 1 M
B. 2 M
C. 0.5 M
D. 3 M

Solution

Molarity (M) = moles of solute / liters of solution = 2 moles / 1 L = 2 M.

Correct Answer: B — 2 M

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Q. If 20 grams of glucose (C6H12O6) is dissolved in 200 mL of solution, what is the mass percent concentration? (Molar mass of glucose = 180 g/mol)

A. 10%
B. 5%
C. 20%
D. 15%

Solution

Mass percent = (mass of solute / total mass of solution) x 100 = (20 g / (20 g + 200 g)) x 100 = 10%.

Correct Answer: A — 10%

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Q. If 4 moles of solute are dissolved in 2 kg of solvent, what is the molality of the solution?

A. 2 m
B. 4 m
C. 1 m
D. 0.5 m

Solution

Molality (m) = moles of solute / kg of solvent = 4 moles / 2 kg = 2 m.

Correct Answer: A — 2 m

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Q. If 5 moles of KCl are dissolved in 1 kg of water, what is the molality of the solution?

A. 5 m
B. 2.5 m
C. 10 m
D. 1 m

Solution

Molality (m) = moles of solute / kg of solvent = 5 moles / 1 kg = 5 m.

Correct Answer: A — 5 m

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Concentration Terms

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