Fundamental Concepts of Chemistry

Fundamental Concepts of Chemistry MDCAT MCQs with answers

81 past paper MCQs from Chemistry unit 1, Fundamental Concepts of Chemistry, across 3 topics. They are arranged topic by topic; bigger topics show a sample here and link to their full set and to study notes. Tap “Show answer” for the correct option and a short solution.

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Moles and Avogadro's Number

1.The mass of one molecule of $\mathrm{O_2}$ is: (MDCAT 2020)

  1. $6.02\times10^{23}/32$ g
  2. $32/6.02\times10^{23}$ g
  3. 32 g
  4. 0.32 g
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Correct answer: (b) $32/6.02\times10^{23}$ g

One mole of $\mathrm{O_2}$ weighs 32 g and holds $6.02\times10^{23}$ molecules, so one molecule is the quotient of the two.

2.The number of moles of $\mathrm{CO_2}$ which contain 8.0 g of oxygen is: (MDCAT 2020)

  1. 1.0
  2. 4.50
  3. 0.50
  4. 0.25
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Correct answer: (d) 0.25

One mole of $\mathrm{CO_2}$ carries 32 g of oxygen, so 8.0 g of oxygen belongs to a quarter of a mole.

3.One mole of any substance contains how many particles? (MDCAT 2020)

  1. $6.02\times10^{23}$
  2. $6.02\times10^{-23}$
  3. $6.02\times10^{32}$
  4. $3.01\times10^{23}$
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Correct answer: (a) $6.02\times10^{23}$

That count is Avogadro's number.

All 61 Moles and Avogadro's Number MCQs → Moles and Avogadro's Number notes →

Yield

4.30 grams of ethanol are mixed with excess acidified $\mathrm{K_2Cr_2O_7}$ and boiled under reflux. The organic product is collected by distillation and the yield is 75.0%. What is the mass of product produced? (MDCAT 2022)

  1. 1.74 g
  2. 24.75 g
  3. 2.74 g
  4. 29 g
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Correct answer: (d) 29 g

$30/46=0.65$ mol of ethanol would give $0.65\times60=39$ g of ethanoic acid, and 75% of that is about 29 g.

5.Consider the given balanced chemical equation: 2H2 + O2 -> 2H2O If 4 g of H2 reacts with 32 g of O2 to produce 28 g of H2O, what is the percentage yield of the reaction? (Molar mass of H2 = 2 g/mol, O2 = 32 g/mol and H2O = 18 g/mol) (UHS MDCAT 2025)

  1. 63.6%
  2. 77.8%
  3. 87.5%
  4. 92.5%
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Correct answer: (b) 77.8%

Four grams of hydrogen would give $36\,\mathrm{g}$ of water, so the yield is $28/36$, or $77.8\%$.

6.A chemical reaction has a theoretical yield of 25 g, but only 20 g of product was obtained. What is the percentage yield of the reaction? (UHS MDCAT 2025)

  1. 20%
  2. 25%
  3. 45%
  4. 80%
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Correct answer: (d) 80%

The yield is the actual over the theoretical, $20/25$, which is $80\%$.

All 12 Yield MCQs → Yield notes →

Limiting and Excess Reactants

7.Consider the given reaction: N2 + 3H2 --> 2NH3 If 56 g of N2 reacts with 12 g of H2 and produces 51 g of NH3, what is the theoretical yield (TY) of NH3 and the percentage yield (PY) of the reaction? (Molar mass of N2 = 28 g/mol, H2 = 2 g/mol and NH3 = 17 g/mol) (SIBA MDCAT 2025)

  1. TY = 68 g and PY = 75%
  2. TY = 34 g and PY = 67%
  3. TY = 68 g and PY = 33%
  4. TY = 34 g and PY = 75%
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Correct answer: (a) TY = 68 g and PY = 75%

Two moles of nitrogen and six of hydrogen are exactly the required ratio, so four moles, $68\,\mathrm{g}$, are possible and $51/68$ is $75\%$.

8.50.0 g Mg is burnt with 32g of oxygen to form MgO, amount of excess reagent left is? (SIBA MDCAT 2025)

  1. 6g Mg
  2. 2g Mg
  3. 8g O2
  4. 16g O2
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Correct answer: (b) 2g Mg

One mole of oxygen needs two moles, $48\,\mathrm{g}$, of magnesium, so $2\,\mathrm{g}$ of magnesium is left over.

9.Ca + S → CaS. If 2.0g of Calcium and 4.0g of Sulphur are available, amount of product formed: (NUMS MDCAT 2024)

  1. 4.6g
  2. 1.6g
  3. 2.6g
  4. 3.6g
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Correct answer: (d) 3.6g

$2.0\,\mathrm{g}$ is $0.05$ mole of calcium, the limiting reactant, so $0.05\times72$, that is $3.6\,\mathrm{g}$, of the sulphide is formed.

All 8 Limiting and Excess Reactants MCQs → Limiting and Excess Reactants notes →

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