JAMB Chemistry questions: Chemical combination

31 questions with answers and explanations. Tap an option to check yourself.

1. Question 21· Chemical combination· JAMB

   Find the mass of 3.01 × 10²³ atoms of sodium. (Na = 23; Avogadro's constant = 6.02 × 10²³ mol⁻¹)

   • A11.5 g
   • B23 g
   • C46 g
   • D6.9 g

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2. Question 22· Chemical combination· JAMB

   0.5 g of a gas occupies 280 cm³ at s.t.p. Find its molar mass. [molar volume = 22.4 dm³]

   • A20 g/mol
   • B40 g/mol
   • C80 g/mol
   • D4 g/mol

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3. Question 23· Chemical combination· JAMB

   How many moles are in 11 g of carbon(IV) oxide? (C = 12, O = 16)

   • A0.25
   • B0.5
   • C1
   • D2

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4. Question 24· Chemical combination· JAMB

   How many molecules are in 0.5 mol of water? (Avogadro's constant = 6.02 × 10²³ mol⁻¹)

   • A1.204 × 10²⁴
   • B6.02 × 10²³
   • C3.01 × 10²³
   • D9 × 10²³

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5. Question 25· Chemical combination· JAMB

   A compound contains 2.4 g of carbon and 0.6 g of hydrogen. Find its empirical formula. (C = 12, H = 1)

   • ACH₄
   • BCH₂
   • CCH₃
   • DC₂H₃

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6. Question 26· Chemical combination· JAMB

   A compound contains 80% carbon and 20% hydrogen by mass, and its molar mass is 30 g/mol. Find its molecular formula. [C = 12, H = 1]

   • AC₂H₄
   • BCH₃
   • CC₂H₆
   • DC₃H₈

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7. Question 27· Chemical combination· JAMB

   A compound has the empirical formula CH₂O and a relative molecular mass of 180. Find its molecular formula. (C = 12, H = 1, O = 16)

   • ACH₂O
   • BC₃H₆O₃
   • CC₆H₁₂O₆
   • DC₁₂H₂₂O₁₁

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8. Question 28· Chemical combination· JAMB

   The statement that in a closed system the total mass of reactants equals the total mass of products is the law of

   • Amultiple proportions
   • Bdefinite proportions
   • Cconservation of mass
   • Dcombining volumes

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9. Question 29· Chemical combination· JAMB

   Find the molar mass of sodium trioxocarbonate(IV), Na₂CO₃. (Na = 23, C = 12, O = 16)

   • A83 g/mol
   • B106 g/mol
   • C62 g/mol
   • D122 g/mol

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10. Question 30· Chemical combination· JAMB

    Find the mass of 0.25 mol of calcium trioxocarbonate(IV), CaCO₃. (Ca = 40, C = 12, O = 16)

    • A12.5 g
    • B100 g
    • C50 g
    • D25 g

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11. Question 31· Chemical combination· JAMB

    In 2H₂ + O₂ → 2H₂O, what volume of oxygen is needed to burn 40 cm³ of hydrogen at the same temperature and pressure?

    • A40 cm³
    • B20 cm³
    • C80 cm³
    • D10 cm³

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