Question

Which of the following is not a balance equation?
(a) Ca(OH) + CO2  CaCO3 + H2O

(b) Fe + CuSO4  FeSO4 + Cu

(c) KClO4  KCl + 2O2

(d) Cu + 2HNO3  Cu(NO3) + 2NO2 +H2O​

Answer 1

"Answer:

d) is not a balanced reaction.

Explanation:

All other reactions have equal amount of atoms on both sides of the reaction but d) is not completely balanced.

Completely balanced d) reaction will be

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

"

Answer 2

$\text { (d) } \mathrm{Cu}+2 \mathrm{HNO3} \rightarrow \mathrm{Cu}(\mathrm{NO} 3) 2+2 \mathrm{NO} 2\text { + H2O. }$

When concentrated nitric acid is dropped on a copper disk in the bottom of a glass cylinder, a reddish-brown cloud of nitrogen dioxide gas is rapidly evolved.

Nitric acid reacts with copper according to the reaction:

$4 \mathrm{HNO}_{3}(I)+\mathrm{Cu}(s)==>\mathrm{Cu}\left(\mathrm{NO}_{3}\right)_{2}(s \text { and } a q)+2 \mathrm{NO}_{2}(g)+2 \mathrm{H}_{2} \mathrm{O}(l)$

The copper nitrate salt that forms is a deep blue color. Nitrogen dioxide is a maroon vapor.

Hence, option

$\text { (d) } \mathrm{Cu}+2 \mathrm{HNO3} \rightarrow \mathrm{Cu}(\mathrm{NO} 3) 2+2 \mathrm{NO} 2\text { + H2O. }$

is not a balanced equation.