How many moles of NO2 will form when 3.3 moles of Cu are reacted with excess HNO3?

6.6 moles.

Explanation:

It is a stichiometric oriented problem. We need to write the balanced chemical equation of the reaction:

Cu + 4HNO₃ → Cu (NO₃) ₂ + 2NO₂ + 2H₂O.

It is clear that 1.0 mole of Cu reacts with 4.0 moles of 4HNO₃ to produce 1.0 mole of Cu (NO₃) ₂, 2.0 moles of NO₂, and 2.0 moles of water.

Now, using cross multiplication:

1.0 mole of Cu produces → 2.0 moles of NO₂, from the stichiometry,

∴ 3.3 moles of Cu produces →? moles of NO₂.

∴ the number of moles of NO₂ will form when 3.3 moles of Cu are reacted with excess HNO₃ is = (3.3 moles of Cu) (2.0 moles of NO₂) / (1.0 mole of Cu) = 6.6 moles.