Chemistry Study Resources for Competitive Exams

Chemistry

Alcohols & Phenols Aldehydes & Ketones Amines Atomic Structure Biomolecules Carboxylic Acids Chemical Bonding Chemical Equilibrium Chemical Kinetics Coordination Compounds d & f-block Elements Electrochemistry Haloalkanes Hydrocarbons Ionic Equilibrium Mole Concept Organic Chemistry Basics p-Block Elements Periodic Table Polymers Redox Reactions Solutions States of Matter Surface Chemistry Thermodynamics

Q. How many molecules are in 0.1 moles of oxygen gas (O2)? (2021)

A. 6.022 x 10^22
B. 6.022 x 10^23
C. 1.2044 x 10^23
D. 3.011 x 10^23

Solution

Number of molecules = moles x Avogadro's number = 0.1 moles x 6.022 x 10^23 molecules/mole = 6.022 x 10^22 molecules.

Correct Answer: A — 6.022 x 10^22

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Q. How many molecules are in 0.25 moles of oxygen gas (O2)? (2022)

A. 3.011 x 10^23
B. 6.022 x 10^22
C. 1.2044 x 10^23
D. 1.5055 x 10^23

Solution

Number of molecules = moles x Avogadro's number = 0.25 moles x 6.022 x 10^23 molecules/mole = 1.5055 x 10^23 molecules.

Correct Answer: B — 6.022 x 10^22

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Q. How many molecules are present in 2 moles of water (H2O)? (2022) 2022

A. 6.022 x 10^23
B. 1.2044 x 10^24
C. 3.011 x 10^23
D. 1.2044 x 10^23

Solution

Number of molecules = moles x Avogadro's number = 2 moles x 6.022 x 10^23 molecules/mole = 1.2044 x 10^24 molecules.

Correct Answer: B — 1.2044 x 10^24

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Q. How many moles are in 100 grams of NaOH? (2022)

A. 2.5
B. 1.25
C. 0.5
D. 3

Solution

Molar mass of NaOH = 23 + 16 + 1 = 40 g/mol. Number of moles = mass/molar mass = 100 g / 40 g/mol = 2.5 moles.

Correct Answer: B — 1.25

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Q. How many moles are in 32 grams of O2? (2021)

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

Solution

Molar mass of O2 = 16*2 = 32 g/mol. Number of moles = mass/molar mass = 32g/32g/mol = 1 mole.

Correct Answer: A — 1

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Q. How many moles of solute are present in 500 mL of a 0.2 M solution? (2021) 2021

A. 0.1 moles
B. 0.5 moles
C. 0.2 moles
D. 0.25 moles

Solution

Moles = Molarity * Volume (L) = 0.2 M * 0.5 L = 0.1 moles.

Correct Answer: A — 0.1 moles

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Q. How many orbitals are present in the d-subshell? (2023)

A. 1
B. 3
C. 5
D. 7

Solution

The d-subshell has 5 orbitals.

Correct Answer: C — 5

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Q. How many orbitals are present in the p subshell? (2023)

A. 1
B. 2
C. 3
D. 5

Solution

The p subshell has 3 orbitals (px, py, pz).

Correct Answer: C — 3

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Q. Identify the oxidizing agent in the reaction: 2H2 + O2 → 2H2O. (2023)

A. H2
B. O2
C. H2O
D. None of the above

Solution

O2 is the oxidizing agent as it gains electrons and is reduced to H2O.

Correct Answer: B — O2

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Q. If 0.1 M acetic acid (CH3COOH) is 1% ionized, what is the concentration of H+ ions?

A. 0.001 M
B. 0.01 M
C. 0.1 M
D. 0.2 M

Solution

Ionization = 1% of 0.1 M = 0.001 M, so [H+] = 0.001 M.

Correct Answer: B — 0.01 M

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Q. If 0.1 M acetic acid has a pH of 2.87, what is the concentration of H+ ions?

A. 0.001 M
B. 0.01 M
C. 0.1 M
D. 0.5 M

Solution

[H+] = 10^(-pH) = 10^(-2.87) ≈ 0.001 M.

Correct Answer: B — 0.01 M

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Q. If 0.5 moles of a gas occupy 12.2 liters at STP, what is the molar volume of the gas? (2023)

A. 22.4 L
B. 24 L
C. 12.2 L
D. 6.1 L

Solution

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

Correct Answer: A — 22.4 L

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Q. If 1 mole of a gas occupies 22.4 liters at STP, how many liters will 0.5 moles occupy? (2023)

A. 11.2 L
B. 22.4 L
C. 44.8 L
D. 5.6 L

Solution

At STP, 1 mole of gas occupies 22.4 L. Therefore, 0.5 moles will occupy 0.5 x 22.4 L = 11.2 L.

Correct Answer: A — 11.2 L

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Q. If 10 g of glucose (C6H12O6) is dissolved in 200 g of water, what is the mass percentage of the solution? (2023)

A. 4.76%
B. 5.00%
C. 10.00%
D. 2.50%

Solution

Mass percentage = (mass of solute / mass of solution) x 100. Mass of solution = 10 g + 200 g = 210 g. Mass percentage = (10 g / 210 g) x 100 = 4.76%.

Correct Answer: A — 4.76%

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Q. If 10 g of sugar (C12H22O11) is dissolved in 200 g of water, what is the mass percentage of the solution? (Molar mass of sugar = 342 g/mol) (2023)

A. 4.76%
B. 5.00%
C. 10.00%
D. 2.50%

Solution

Mass percentage = (mass of solute / mass of solution) x 100. Mass of solution = 10 g + 200 g = 210 g. Mass percentage = (10 g / 210 g) x 100 = 4.76%.

Correct Answer: B — 5.00%

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Q. If 10 g of sugar (C12H22O11) is dissolved in 200 g of water, what is the mass percentage of the sugar solution? (Molar mass of sugar = 342 g/mol) (2023)

A. 4.76%
B. 5.00%
C. 10.00%
D. 2.50%

Solution

Mass percentage = (mass of solute / mass of solution) x 100. Mass of solution = 10 g + 200 g = 210 g. Mass percentage = (10 g / 210 g) x 100 = 4.76%.

Correct Answer: A — 4.76%

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Q. If 10 g of sugar (C12H22O11) is dissolved in 200 g of water, what is the mass percent of sugar in the solution? (Molar mass of sugar = 342 g/mol) (2023)

A. 4.76%
B. 5.00%
C. 10.00%
D. 2.50%

Solution

Mass percent = (mass of solute / total mass of solution) x 100. Total mass = 10 g + 200 g = 210 g. Mass percent = (10 g / 210 g) x 100 = 4.76%.

Correct Answer: A — 4.76%

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Q. If 10 g of sugar is dissolved in 100 g of water, what is the mass percent of sugar in the solution? (2023)

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

Solution

Mass percent = (mass of solute / total mass of solution) x 100. Total mass = 10 g + 100 g = 110 g. Mass percent = (10 g / 110 g) x 100 = 9.09%, approximately 10%.

Correct Answer: A — 10%

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Q. If 10 g of sugar is dissolved in 100 g of water, what is the mass percentage of sugar in the solution? (2023)

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

Solution

Mass percentage = (mass of solute / mass of solution) × 100. Mass of solution = 10 g + 100 g = 110 g. Mass percentage = (10 g / 110 g) × 100 = 9.09%, approximately 10%.

Correct Answer: A — 10%

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Q. If 10 grams of NaCl is dissolved in 500 mL of water, what is the concentration in g/L? (2020)

A. 20 g/L
B. 10 g/L
C. 5 g/L
D. 15 g/L

Solution

Concentration = (10 g / 0.5 L) = 20 g/L.

Correct Answer: A — 20 g/L

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Q. If 10 grams of NaCl is dissolved in 500 mL of water, what is the mass/volume percent concentration? (2020) 2020

A. 2%
B. 5%
C. 10%
D. 20%

Solution

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

Correct Answer: B — 5%

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Q. If 15 g of sugar is dissolved in 300 mL of water, what is the concentration in g/mL? (2020)

A. 0.05 g/mL
B. 0.1 g/mL
C. 0.15 g/mL
D. 0.2 g/mL

Solution

Concentration = mass / volume = 15 g / 300 mL = 0.05 g/mL.

Correct Answer: B — 0.1 g/mL

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Q. If 20 grams of glucose (C6H12O6) is dissolved in 1 liter of water, what is the molarity of the solution? (Molar mass of glucose = 180 g/mol) (2020) 2020

A. 0.11 M
B. 0.5 M
C. 0.2 M
D. 0.33 M

Solution

Moles of glucose = 20 g / 180 g/mol = 0.111 M. Molarity = 0.111 moles / 1 L = 0.11 M.

Correct Answer: A — 0.11 M

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Q. If 3 moles of glucose are dissolved in 1 liter of solution, what is the molality of the solution? (2023)

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

Solution

Molality (m) = moles of solute / kg of solvent; assuming 1 L of water = 1 kg, m = 3 moles / 1 kg = 3 m

Correct Answer: A — 3 m

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Q. If 50 mL of 0.1 M H2SO4 is diluted to 250 mL, what is the new concentration?

A. 0.02 M
B. 0.04 M
C. 0.1 M
D. 0.5 M

Solution

C1V1 = C2V2; (0.1 M)(50 mL) = C2(250 mL); C2 = 0.02 M.

Correct Answer: B — 0.04 M

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Q. If 50 mL of a 3 M solution is diluted to 200 mL, what is the new molarity? (2020)

A. 0.75 M
B. 1.5 M
C. 2 M
D. 3 M

Solution

Using M1V1 = M2V2, (3 M)(50 mL) = M2(200 mL) => M2 = (3 M × 50 mL) / 200 mL = 0.75 M.

Correct Answer: A — 0.75 M

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Q. If the concentration of a reactant is tripled in a second-order reaction, how does the rate change? (2023)

A. Increases by 3 times
B. Increases by 6 times
C. Increases by 9 times
D. Increases by 12 times

Solution

For a second-order reaction, if concentration is tripled, the rate increases by 3² = 9 times.

Correct Answer: C — Increases by 9 times

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Q. If the concentration of Cu²⁺ in a cell is increased, what happens to the cell potential?

A. Increases
B. Decreases
C. Remains the same
D. Becomes zero

Solution

Increasing the concentration of Cu²⁺ increases the cell potential according to the Nernst equation.

Correct Answer: A — Increases

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Q. If the pH of a solution is 3, what is the concentration of H+ ions? (2023)

A. 0.001 M
B. 0.01 M
C. 0.1 M
D. 0.0001 M

Solution

pH = 3 means [H+] = 10^-3 M = 0.001 M.

Correct Answer: B — 0.01 M

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Q. If the pKa of acetic acid is 4.76, what is the pH of a 0.1 M solution?

A. 4.76
B. 5.76
C. 6.76
D. 3.76

Solution

For a weak acid, pH ≈ pKa for a 0.1 M solution, so pH ≈ 4.76.

Correct Answer: A — 4.76

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Chemistry

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