Balance the following reaction equation: Cu + HNO₃ → Cu(NO₃)₂ + NO + H₂O
A) 3, 8, 3, 2, 4
B) 2, 6, 3, 2, 4
C) 3, 8, 3, 1, 4
D) 3, 8, 3, 2, 6
E) None of the other options is correct
IMAT 2026 · Question 34
Q34 - Balancing chemical equations
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The correct answer is A) 3, 8, 3, 2, 4.
Balance it using electron transfer: the electrons lost must equal the electrons gained.
Cu: 0 → +2 (loses 2 e⁻) and N: +5 → +2 in NO (gains 3 e⁻). The least common multiple of 2 and 3 is 6, so we need 3 Cu and 2 NO.
3 Cu + ? HNO₃ → 3 Cu(NO₃)₂ + 2 NO + ? H₂O
Nitrogen: 3 × 2 = 6 N in Cu(NO₃)₂, plus 2 N in NO, gives 8 HNO₃. Hydrogen: 8 H on the left gives 4 H₂O.
Check oxygen: left 8 × 3 = 24; right 3 × 6 + 2 + 4 = 24. Everything balances: 3, 8, 3, 2, 4.
The other options fail a check: in B, 2 Cu cannot make 3 Cu(NO₃)₂; in C, 1 NO leaves only 7 N on the right; in D, 6 H₂O needs 12 H, but there are only 8.
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