Question

1. last one! predict the mass of the solid that remains if reaction #4 occurs.

balance reaction #4.
i need a hint
$\boldsymbol{?\\ nahco_3(s) \
ightarrow ?\\ na_2co_3(s) + ?\\ co_2(g) + ?\\ h_2o(g)}$
choices:
1
2
3
4

Explanation:

Step1: Balance sodium atoms

Count Na on right: 2 in $\text{Na}_2\text{CO}_3$. Add coefficient 2 to $\text{NaHCO}_3$:
$2\text{NaHCO}_3(s)
ightarrow ?\text{Na}_2\text{CO}_3(s) + ?\text{CO}_2(g) + ?\text{H}_2\text{O}(g)$

Step2: Balance carbon atoms

Left C: 2. Right: 1 in $\text{Na}_2\text{CO}_3$, so add 1 to $\text{CO}_2$:
$2\text{NaHCO}_3(s)
ightarrow ?\text{Na}_2\text{CO}_3(s) + 1\text{CO}_2(g) + ?\text{H}_2\text{O}(g)$

Step3: Balance hydrogen atoms

Left H: 2. Add 1 to $\text{H}_2\text{O}$:
$2\text{NaHCO}_3(s)
ightarrow ?\text{Na}_2\text{CO}_3(s) + 1\text{CO}_2(g) + 1\text{H}_2\text{O}(g)$

Step4: Balance oxygen & confirm

Left O: $2\times3=6$. Right: $3 + 2 + 1=6$. Add 1 to $\text{Na}_2\text{CO}_3$:
$2\text{NaHCO}_3(s)
ightarrow 1\text{Na}_2\text{CO}_3(s) + 1\text{CO}_2(g) + 1\text{H}_2\text{O}(g)$

Answer:

The balanced coefficients (in order) are 2, 1, 1, 1. The coefficient for $\text{NaHCO}_3$ is $\boldsymbol{2}$.