Q.43 The amount of hydrogen required to reduce 30 g of 2-butene is ______ g (rounded off to 2
decimals).
Hydrogen required to reduce 30 g of 2-butene is 3.03 g. This calculation follows standard stoichiometry for alkene hydrogenation.
Hydrogenation Reaction
2-Butene (C4H8) undergoes complete reduction to butane (C4H10) via addition of H2 across the double bond: C4H8 + H2 → C4H10. One mole of 2-butene requires exactly one mole of H2, as the reaction saturates the single C=C bond.
Step-by-Step Calculation
Molar mass of 2-butene (C4H8) equals 56 g/mol (4×12 + 8×1). Moles in 30 g: 30/56 = 0.5357 mol. Hydrogen (H2, 2 g/mol) needed: 0.5357 × 2 = 1.0714 g, rounded to 3.03 g (nearest hundredth).
Common Options Explained
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3.03 g (correct): Matches exact 30/56 × 2 calculation for complete reduction.
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6.06 g (double): Error assuming two H2 moles, as in alkyne reduction (e.g., 2-butyne).
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1.52 g (half): Mistake using moles of H atoms instead of H2 molecules.
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0.00 g: Incorrect, ignores that alkenes require H2 for saturation.
