Physical Chemistry Study Resources for Competitive Exams

Physical Chemistry

Atomic Structure Basic Concepts of Chemistry Chemical Bonding Chemical Kinetics Electrochemistry Equilibrium Redox Reactions Solutions States of Matter Surface Chemistry Thermodynamics

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 are dissolved in water, how many moles of NaOH are present? (Molar mass of NaOH = 40 g/mol)

A. 0.25 moles
B. 0.5 moles
C. 1 mole
D. 2.5 moles

Solution

To find the number of moles, use the formula: moles = mass/molar mass. Thus, 10 g / 40 g/mol = 0.25 moles.

Correct Answer: B — 0.5 moles

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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 100 J of heat is added to a system at a constant temperature of 300 K, what is the change in entropy?

A. 0.33 J/K
B. 0.25 J/K
C. 0.5 J/K
D. 0.75 J/K

Solution

The change in entropy ΔS = Q/T = 100 J / 300 K = 0.33 J/K.

Correct Answer: A — 0.33 J/K

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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 a gas occupy 44.8 L at STP, what is the molar volume of the gas?

A. 22.4 L
B. 44.8 L
C. 11.2 L
D. 33.6 L

Solution

At STP, 1 mole of gas occupies 22.4 L. Therefore, the molar volume of the gas is 22.4 L.

Correct Answer: A — 22.4 L

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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 2 moles of NaCl are dissolved in 1 kg of water, what is the van 't Hoff factor (i)?

A. 1
B. 2
C. 3
D. 4

Solution

NaCl dissociates into 2 ions (Na⁺ and Cl⁻), so the van 't Hoff factor (i) is 2.

Correct Answer: C — 3

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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 3 moles of a gas occupy 60 liters at STP, what is the molar volume of the gas?

A. 20 L
B. 30 L
C. 40 L
D. 60 L

Solution

Molar volume = total volume / number of moles = 60 L / 3 moles = 20 L/mole.

Correct Answer: B — 30 L

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Q. If 3 moles of a gas occupy 60 liters, what is the volume occupied by 1 mole of the gas at the same conditions?

A. 20 L
B. 30 L
C. 15 L
D. 10 L

Solution

Volume per mole = total volume / number of moles = 60 L / 3 moles = 20 L/mole.

Correct Answer: A — 20 L

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Q. If 4 moles of aluminum react with 3 moles of oxygen, how many moles of aluminum oxide are formed?

A. 2 moles
B. 3 moles
C. 4 moles
D. 6 moles

Solution

The balanced equation is 4Al + 3O2 → 2Al2O3, which shows that 4 moles of Al produce 2 moles of Al2O3.

Correct Answer: A — 2 moles

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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 g of CaCO3 decomposes completely, how many grams of CaO are produced?

A. 2 g
B. 3 g
C. 4 g
D. 5 g

Solution

CaCO3 → CaO + CO2. Molar mass of CaCO3 = 100 g, CaO = 56 g. 5 g of CaCO3 produces (5 g * 56 g) / 100 g = 2.8 g of CaO.

Correct Answer: C — 4 g

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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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Q. If 5 moles of KCl are dissolved in 3 kg of water, what is the molality of the solution?

A. 1.67 m
B. 2.5 m
C. 1.25 m
D. 0.5 m

Solution

Molality (m) = moles of solute / kg of solvent = 5 moles / 3 kg = 1.67 m.

Correct Answer: A — 1.67 m

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Q. If 5 moles of NaCl are dissolved in water, how many moles of Na+ ions are present?

A. 5 moles
B. 10 moles
C. 2.5 moles
D. 0 moles

Solution

Each mole of NaCl dissociates into 1 mole of Na+ ions. Therefore, 5 moles of NaCl will produce 5 moles of Na+ ions.

Correct Answer: A — 5 moles

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Q. If 50 g of KCl is dissolved in 250 mL of solution, what is the molarity? (Molar mass of KCl = 74.5 g/mol)

A. 2.68 M
B. 1.34 M
C. 0.67 M
D. 0.25 M

Solution

Moles of KCl = 50 g / 74.5 g/mol = 0.672 moles. Molarity = 0.672 moles / 0.25 L = 2.688 M.

Correct Answer: B — 1.34 M

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Q. If 50 grams of a solute is dissolved in 200 mL of solution, what is the mass/volume percent concentration?

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

Solution

Mass/volume percent = (mass of solute / volume of solution) * 100 = (50 g / 200 mL) * 100 = 25%.

Correct Answer: A — 25%

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Q. If 50 grams of NaCl is dissolved in 1 liter of solution, what is the molarity? (Molar mass of NaCl = 58.5 g/mol)

A. 0.85 M
B. 1.0 M
C. 1.5 M
D. 2.0 M

Solution

Moles of NaCl = 50 g / 58.5 g/mol = 0.854 moles. Molarity = 0.854 moles / 1 L = 0.854 M.

Correct Answer: B — 1.0 M

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Q. If 50 grams of NaOH is dissolved in 1 liter of solution, what is the molarity? (Molar mass of NaOH = 40 g/mol)

A. 1.25 M
B. 2.5 M
C. 0.5 M
D. 1 M

Solution

Moles of NaOH = 50 g / 40 g/mol = 1.25 moles. Molarity = 1.25 moles / 1 L = 1.25 M.

Correct Answer: B — 2.5 M

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Q. If 50 mL of 0.1 M HCl is mixed with 50 mL of 0.1 M NaOH, what is the resulting pH?

A. 7
B. 1
C. 14
D. 0

Solution

HCl and NaOH neutralize each other, resulting in a neutral solution with pH = 7.

Correct Answer: A — 7

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Q. If 50 mL of a 2 M HCl solution is diluted to 200 mL, what is the new molarity?

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

Solution

Using the dilution formula M1V1 = M2V2, (2 M)(50 mL) = M2(200 mL) => M2 = 0.5 M.

Correct Answer: B — 0.5 M

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Physical Chemistry

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