Which substance has a coefficient of 2 when you balance the equation for this redox reaction? cu (s) + hno3 (aq) → cu (no3) 2 (aq) + no (g) + h2o (l) hno3 (aq) no (g) h2o (l) cu (s) ?

In this redox reaction, the Cu goes from oxidation state of (0) to (+2), therefore it oxidises. N in HNO₃ goes from oxidation state of (+5) to N in NO with oxidation state of (+2) and becomes reduced.

Cu acts as the reducing reagent and HNO₃ is the oxidising agent.

oxidation half reaction

Cu - - - > Cu²⁺ + 2e - - 1)

reduction half reaction

4H⁺ + 3e + NO₃⁻ - - - > NO + 2H₂O - - 2)

to balance the number of electrons, 1) x3 and 2) x2

3Cu - - - > 3Cu²⁺ + 6e

8H⁺ + 6e + 2NO₃⁻ - - - > 2NO + 4H₂O

add the 2 equations

3Cu + 8H⁺ + 2NO₃⁻ - - - > 3Cu²⁺ + 2NO + 4H₂O

add 6 nitrate ions to both sides to add up to 8 and form acid with 8H⁺ ions

3Cu + 8HNO₃ - - - > 3Cu (NO₃) ₂ + 2NO + 4H₂O

Balanced equation for the redox reaction is as follows;

3Cu (s) + 8HNO₃ (aq) → 3Cu (NO₃) ₂ (aq) + 2NO (g) + 4H₂O (l)

NO has a coefficient of 2