How would you balance the following equation: Ca+HNO3 --> Ca(NO3)2+ N2O3+ H2O?

1 Answer
Feb 11, 2016

Answer:

By the method of half-equations: calcium metal is oxidized, and nitrogen is reduced.

Explanation:

Oxidation:

#Ca(s) rarr Ca^(2+) + 2e^-# #(i)#

Reduction:

#2HNO_3(aq) +4e^(-) +4H^(+) rarr N_2O_3 +3H_2O# #(ii)#

Note that dinitrogen trioxide is a metastable species, and is a mixed valence oxide of #N(II+)# and #N(IV+)#, hence an average oxidation state of #III+#.

Both #(i)# and #(ii)# are balanced with respect to mass and charge (as they must be!). We add #2xx(i) +(ii)# to give:

#2Ca(s) + 2HNO_3(aq) +4H^(+) rarr 2Ca^(2+) + N_2O_3(aq) +3H_2O(aq)#

Since the source of #H^+# is undoubtedly nitric acid, we could write:

#2Ca(s) + 6HNO_3(aq) rarr 2Ca(NO_3)_2 + N_2O_3(aq) +3H_2O(aq)#

Is this last equation balanced with respect to mass and charge? Do not trust my arithmetic!