Use these chemistry practice questions to review atomic structure, the periodic table, chemical bonding, reactions, stoichiometry, solutions, acids and bases, thermochemistry, equilibrium, and oxidation-reduction reactions. Work each problem before opening the answer explanation.
Topics Covered
- Atomic number, mass number, and isotopes
- Periodic-table groups and chemical properties
- Ionic compounds and charge balance
- Balancing chemical equations
- Moles and molar mass
- Molarity
- Acids, hydrogen-ion concentration, and pH
- Exothermic reactions and enthalpy
- Chemical equilibrium and Le Châtelier’s principle
- Oxidation and reduction
Sample Questions
- A. 17
- B. 20
- C. 37
- D. 54
Show Answer
The atomic number gives the number of protons, so chlorine-37 has 17 protons.
The mass number equals protons plus neutrons. Therefore, 37 − 17 = 20 neutrons.
- A. Sodium and potassium
- B. Sodium and chlorine
- C. Carbon and neon
- D. Magnesium and sulfur
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Elements in the same vertical group of the periodic table tend to have similar chemical properties because they have similar valence-electron configurations.
Sodium and potassium are both Group 1 alkali metals.
- A. MgCl
- B. MgCl2
- C. Mg2Cl
- D. Mg2Cl2
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An ionic compound must have an overall charge of zero.
One Mg2+ ion requires two Cl− ions to balance the charge, giving MgCl2.
- A. 1
- B. 2
- C. 3
- D. 4
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The balanced equation is 2H2 + O2 → 2H2O.
This gives four hydrogen atoms and two oxygen atoms on each side.
- A. 0.50 mol
- B. 1.00 mol
- C. 2.00 mol
- D. 18.0 mol
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Use moles = mass ÷ molar mass.
36.0 g ÷ 18.0 g/mol = 2.00 mol.
- A. 0.10 M
- B. 0.25 M
- C. 1.0 M
- D. 4.0 M
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Molarity is moles of solute divided by liters of solution.
0.50 mol ÷ 2.0 L = 0.25 M.
- A. 1
- B. 3
- C. 7
- D. 11
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Use pH = −log[H+].
For [H+] = 1 × 10−3 M, the pH is 3.
- A. The reaction absorbs heat from its surroundings, and ΔH is positive.
- B. The reaction releases heat to its surroundings, and ΔH is negative.
- C. The reaction must occur only at temperatures below 0°C.
- D. The products always contain more energy than the reactants.
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An exothermic reaction transfers heat from the reacting system to the surroundings.
Because the products have lower enthalpy than the reactants, ΔH is negative.
- A. The equilibrium shifts toward the reactants.
- B. The equilibrium shifts toward the products.
- C. The equilibrium constant becomes zero.
- D. The reaction immediately stops.
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The reactant side has four moles of gas for every two moles of gas on the product side.
Increasing pressure favors the side with fewer gas particles, so equilibrium shifts toward ammonia.
- A. It is oxidized because it loses electrons.
- B. It is reduced because it loses electrons.
- C. It is oxidized because it gains electrons.
- D. It is reduced because it gains protons.
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Oxidation is the loss of electrons.
The zinc atom loses two electrons as it becomes Zn2+, so zinc is oxidized.
How to Use These Questions
Identify the chemistry principle being tested before calculating. Write down known quantities, include units throughout the calculation, and check whether the final result is chemically reasonable.
For reaction questions, verify that both atoms and electric charge are conserved. For oxidation-reduction questions, remember that oxidation is loss of electrons and reduction is gain of electrons.