PMC National MDCAT Chemistry Fundamental Concepts — Set 2

Fundamental Concepts MCQs set 2 for PMC National MDCAT Chemistry — 20 solved questions.

PMC National MDCAT Chemistry Fundamental Concepts — Set 2

  1. Question 1

    Q1. How many molecules are present in 0.25 moles of ammonia (NH₃)?

    • A) 1.5 × 10²³
    • B) 2.4 × 10²³
    • C) 3.0 × 10²³
    • D) 6.022 × 10²³

    Answer: 1.5 × 10²³

    Explanation: 0.25 × 6.022 × 10²³ = 1.5 × 10²³. Option C uses Avogadro’s number directly.

  2. Question 2

    Q2. What volume (in liters) does 0.5 moles of O₂ occupy at STP? (Molar volume = 22.4 L/mol)

    • A) 11.2 L
    • B) 22.4 L
    • C) 44.8 L
    • D) 5.6 L

    Answer: 11.2 L

    Explanation: 0.5 × 22.4 = 11.2 L. Option B ignores moles given.

  3. Question 3

    Q3. A gas at 2 atm and 300 K occupies 10 L. What is its volume at 3 atm and 600 K? (R = 0.0821 L·atm/mol·K)

    • A) 15 L
    • B) 10 L
    • C) 7.5 L
    • D) 5 L

    Answer: 10 L

    Explanation: Using PV/T = constant: (2×10)/300 = (3×V)/600 → V = 10 L. Option A misapplies gas law ratios.

  4. Question 4

    Q4. What mass of NaOH (molar mass = 40 g/mol) is required to prepare 500 mL of 0.2 M solution?

    • A) 4 g
    • B) 8 g
    • C) 2 g
    • D) 0.5 g

    Answer: 4 g

    Explanation: 0.5 L × 0.2 mol/L × 40 g/mol = 4 g. Option C halves volume incorrectly.

  5. Question 5

    Q5. A compound contains 40% C, 6.67% H, and 53.3% O by mass. What is its empirical formula?

    • A) CH₂O
    • B) C₂H₄O₂
    • C) CHO
    • D) CH₄O

    Answer: CH₂O

    Explanation: Mole ratio: 3.33 C : 6.67 H : 3.33 O → 1:2:1. Option D adds extra hydrogen.

  6. Question 6

    Q6. How many moles of H₂O are produced when 2 moles of C₃H₈ combust completely? (Balanced equation: C₃H₈ + 5O₂ → 3CO₂ + 4H₂O)

    • A) 4 moles
    • B) 6 moles
    • C) 8 moles
    • D) 2 moles

    Answer: 8 moles

    Explanation: 2 moles C₃H₈ × 4 H₂O/1 C₃H₈ = 8 moles. Option A ignores stoichiometric ratio.

  7. Question 7

    Q7. What is the molarity of a 30 mL HCl solution that neutralizes 20 mL of 0.15 M NaOH?

    • A) 0.1 M
    • B) 0.2 M
    • C) 0.3 M
    • D) 0.4 M

    Answer: 0.1 M

    Explanation: M₁V₁ = M₂V₂ → M₁ = (0.15×20)/30 = 0.1 M. Option C swaps volumes.

  8. Question 8

    Q8. How many liters of CO₂ (at STP) are produced from 11.2 L of O₂ in the reaction 2CO + O₂ → 2CO₂?

    • A) 22.4 L
    • B) 11.2 L
    • C) 5.6 L
    • D) 44.8 L

    Answer: 22.4 L

    Explanation: 1 mole O₂ → 2 moles CO₂. 11.2 L O₂ × 2 = 22.4 L CO₂. Option B ignores mole ratio.

  9. Question 9

    Q9. What is the mass of 3.01 × 10²³ molecules of glucose (C₆H₁₂O₆, molar mass = 180 g/mol)?

    • A) 90 g
    • B) 180 g
    • C) 30 g
    • D) 60 g

    Answer: 90 g

    Explanation: 3.01×10²³ / 6.02×10²³ = 0.5 mol → 0.5 × 180 = 90 g. Option C divides by 2 incorrectly.

  10. Question 10

    Q10. A gas cylinder contains 10 L of O₂ at 2 atm. What pressure is needed to compress it to 5 L at constant temperature?

    • A) 1 atm
    • B) 2 atm
    • C) 4 atm
    • D) 8 atm

    Answer: 4 atm

    Explanation: P₁V₁ = P₂V₂ → 2×10 = P×5 → P = 4 atm. Option B ignores volume change.

  11. Question 11

    Q11. What volume of 0.5 M H₂SO₄ is required to neutralize 25 mL of 0.1 M NaOH?

    • A) 2.5 mL
    • B) 5 mL
    • C) 10 mL
    • D) 20 mL

    Answer: 2.5 mL

    Explanation: Moles NaOH = 0.025×0.1 = 0.0025. H₂SO₄ is diprotic: 0.00125 / 0.5 = 0.0025 L = 2.5 mL. Option B ignores dilution.

  12. Question 12

    Q12. What is the mass of 0.2 moles of CaCO₃ (molar mass = 100 g/mol)?

    • A) 20 g
    • B) 40 g
    • C) 60 g
    • D) 100 g

    Answer: 20 g

    Explanation: 0.2 × 100 = 20 g. Option B triples the value.

  13. Question 13

    Q13. A solution contains 1.204 × 10²³ atoms of Mg. How many moles is this?

    • A) 0.2 mol
    • B) 0.4 mol
    • C) 0.6 mol
    • D) 0.8 mol

    Answer: 0.2 mol

    Explanation: 1.204×10²³ / 6.022×10²³ = 0.2 mol. Option C doubles the value.

  14. Question 14

    Q14. What is the molarity of a solution containing 9.8 g of H₂SO₄ (molar mass = 98 g/mol) in 250 mL?

    • A) 0.2 M
    • B) 0.4 M
    • C) 0.6 M
    • D) 0.8 M

    Answer: 0.4 M

    Explanation: 9.8/98 = 0.1 mol in 0.25 L → 0.4 M. Option A divides by 250 mL directly.

  15. Question 15

    Q15. How many grams of NaCl are in 500 mL of 0.9% (m/v) physiological saline?

    • A) 4.5 g
    • B) 9.0 g
    • C) 1.8 g
    • D) 0.9 g

    Answer: 4.5 g

    Explanation: 0.9% of 500 mL = 4.5 g. Option C divides by 2.

  16. Question 16

    Q16. What is the volume of 0.25 mol of gas at 1.5 atm and 300 K? (R = 0.0821 L·atm/mol·K)

    • A) 4.0 L
    • B) 3.0 L
    • C) 2.0 L
    • D) 1.0 L

    Answer: 4.0 L

    Explanation: V = nRT/P = (0.25×0.0821×300)/1.5 = 4.0 L. Option B halves the pressure.

  17. Question 17

    Q17. A 0.250 L solution contains 5.0 g of NaCl. What is its molarity? (Molar mass of NaCl = 58.44 g/mol)

    • A) 0.31 M
    • B) 0.34 M
    • C) 0.17 M
    • D) 0.68 M

    Answer: 0.34 M

    Explanation: Molarity = (5.0/58.44)/0.250 = 0.34 M. A fails to account for significant figures.

  18. Question 18

    Q18. What volume of 0.500 M HCl is required to neutralize 25.0 mL of 0.200 M Ca(OH)₂?

    • A) 10.0 mL
    • B) 20.0 mL
    • C) 40.0 mL
    • D) 5.0 mL

    Answer: 40.0 mL

    Explanation: 2×0.200×0.025 /0.500 = 0.04 L = 40.0 mL. B ignores 2:1 molar ratio.

  19. Question 19

    Q19. A gas occupies 3.00 L at 300 K and 1.00 atm. What is its volume at 373 K and 0.800 atm?

    • A) 3.78 L
    • B) 4.62 L
    • C) 5.12 L
    • D) 2.85 L

    Answer: 4.62 L

    Explanation: V₂ = (1×3×373)/(0.8×300) = 4.62 L. A uses incorrect temperature order.

  20. Question 20

    Q20. How many moles of O₂ are in 15.0 L at STP? (Molar volume = 22.4 L/mol)

    • A) 0.670 mol
    • B) 0.336 mol
    • C) 0.660 mol
    • D) 0.333 mol

    Answer: 0.670 mol

    Explanation: 15.0/22.4 = 0.670 mol. C uses 22.7 L/mol as molar volume.

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Level 1

How many molecules are present in 0.25 moles of ammonia (NH₃)?