MDCAT Chemistry chapter 1: Chemistry · Fundamental concepts of chemistry MCQs with answers

By Team Megalecture · Updated 4 Nov 2026

34 exam-style questions on Chemistry · Fundamental concepts of chemistry, each with the answer and a short explanation. Ten of them are below to try. The chapter test draws ten fresh questions each time and is marked the moment you finish, with your score by topic.

34 questions · 2 topics · 10 per test

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What chapter 1 covers

Ten Chemistry · Fundamental concepts of chemistry questions with answers

Try each one, then open the answer. These ten stay the same; the test draws new ones every time.

1. What mass of calcium carbonate, CaCO3, contains 4.8 g of oxygen? (C = 12, O = 16, Ca = 40)

  1. A
    10 g
  2. B
    30 g
  3. C
    15 g
  4. D
    5.0 g
Show answer

Answer: A. 4.8 ÷ 16 = 0.30 mol of O atoms, and each CaCO3 unit holds three O atoms, so 0.10 mol of CaCO3 = 0.10 × 100 = 10 g is needed. 30 g ignores the three O atoms per formula unit, and 15 g treats the oxygen as O2 (32 g mol−1).

2. Which pair of compounds has the same empirical formula?

  1. A
    C2H4 and C2H6
  2. B
    CH4 and C2H6
  3. C
    C2H2 and C6H6
  4. D
    H2O and H2O2
Show answer

Answer: C. Ethyne, C2H2, and benzene, C6H6, both reduce to CH. The other pairs give CH2 and CH3, CH4 and CH3, and H2O and HO: having the same elements is not enough.

3. Ammonium nitrate, NH4NO3, is used as a fertiliser. What is its percentage of nitrogen by mass? (H = 1, N = 14, O = 16)

  1. A
    17.5%
  2. B
    35.0%
  3. C
    60.0%
  4. D
    5.0%
Show answer

Answer: B. M = 80 g mol−1 and the formula contains two N atoms (28 g): 28 ÷ 80 × 100 = 35.0%. Counting only one N gives 17.5%; 60.0% and 5.0% are the shares of oxygen and hydrogen.

4. When 0.10 mol of propane, C3H8, burns completely in excess oxygen, how many moles of water are formed?

  1. A
    0.30 mol
  2. B
    0.50 mol
  3. C
    0.40 mol
  4. D
    0.80 mol
Show answer

Answer: C. C3H8 + 5O2 → 3CO2 + 4H2O, so 0.10 mol of propane gives 0.40 mol of water. 0.30 mol is the CO2, 0.50 mol the O2 used, and 0.80 mol counts H atoms instead of H2O molecules.

5. 10.0 g of calcium carbonate is heated strongly in an open crucible until its mass stops changing, leaving 5.6 g of calcium oxide. How is this fall in mass consistent with the law of conservation of mass?

  1. A
    about 4.4 g of the solid was turned into heat energy
  2. B
    some of the calcium escaped from the open crucible as vapour
  3. C
    the other product, 4.4 g of CO2 gas, escaped into the air
  4. D
    the law does not apply when a compound decomposes
Show answer

Answer: C. CaCO3 → CaO + CO2: the products together weigh as much as the reactant, 10.0 = 5.6 + 4.4 g, but the CO2 escapes from an open crucible. In a closed vessel no change in mass would be seen, and ordinary reactions turn no measurable mass into energy.

6. A hydrocarbon contains 80% carbon and 20% hydrogen by mass. What is its empirical formula? (H = 1, C = 12)

  1. A
    CH3
  2. B
    CH2
  3. C
    C4H
  4. D
    CH4
Show answer

Answer: A. Moles in 100 g: C = 80 ÷ 12 = 6.67 and H = 20 ÷ 1 = 20, a ratio of 1 : 3, so CH3 (ethane, C2H6, has this empirical formula). C4H wrongly uses the mass ratio 80 : 20 as the atom ratio.

7. Which of these calculations is an example of a mass–volume stoichiometric relationship?

  1. A
    the volume of CO2 at STP from 10 g of CaCO3
  2. B
    the mass of CaO formed by heating 10 g of CaCO3
  3. C
    the moles of NH3 formed from 3 mol of H2
  4. D
    the volume of O2 needed to burn 2 dm3 of CO
Show answer

Answer: A. Starting from the mass of one substance (CaCO3) and finding the volume of a gas (CO2) is a mass–volume problem. The others are mass–mass, mole–mole and volume–volume relationships; all of them use the mole ratio from the balanced equation.

8. Ammonia burns in oxygen: 4NH3 + 3O2 → 2N2 + 6H2O. How many moles of oxygen react completely with 2.0 mol of ammonia?

  1. A
    1.5 mol
  2. B
    2.7 mol
  3. C
    3.0 mol
  4. D
    2.0 mol
Show answer

Answer: A. NH3 : O2 = 4 : 3, so O2 = 2.0 × 3/4 = 1.5 mol. Inverting the ratio (2.0 × 4/3) gives 2.7 mol.

9. A mixture of 3.0 mol of hydrogen and 2.0 mol of oxygen is exploded: 2H2 + O2 → 2H2O. Which reactant is left over, and how much?

  1. A
    0.5 mol of O2
  2. B
    1.0 mol of H2
  3. C
    1.0 mol of O2
  4. D
    0.5 mol of H2
Show answer

Answer: A. 3.0 mol H2 needs only 1.5 mol O2, so hydrogen is limiting and 2.0 − 1.5 = 0.5 mol of O2 remains. Hydrogen would be left over only if it were in excess, which needs more than 4.0 mol of it.

10. How many hydrogen atoms are present in 3.4 g of ammonia, NH3? (H = 1, N = 14; NA = 6.02 × 1023 mol−1)

  1. A
    1.204 × 1023
  2. B
    3.612 × 1023
  3. C
    4.816 × 1023
  4. D
    1.806 × 1024
Show answer

Answer: B. 3.4 ÷ 17 = 0.20 mol NH3, which holds 3 × 0.20 = 0.60 mol of H atoms = 0.60 × 6.02 × 1023 = 3.612 × 1023. 1.204 × 1023 is the number of molecules, and 4.816 × 1023 counts all four atoms of each molecule.

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Chemistry · Fundamental concepts of chemistry: questions students ask

How many Chemistry · Fundamental concepts of chemistry MCQs are there?

34, each with the answer and a short explanation, across 2 topics: The mole, Stoichiometry. Every chapter test draws ten of them, so you can take it many times.

Is the MDCAT Chemistry chapter 1 test free?

Yes. The test, the answers and the explanations are free and need no sign-up. Sign in only if you want your scores kept across devices.

How is the chapter test marked?

The moment you press Finish: your score, the right answer and an explanation for every question, and the ones you got wrong saved in My mistakes to retry.

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