# What is the molecular formula of HCO2 with the molar mass of 90.0 g/mol?

Empirical formula $=$ $H C {O}_{2}$. The molecular formula (the multiple!) is ${\left(H C {O}_{2}\right)}_{n}$. So $\left(1.00794 + 12.011 + 2 \times 15.999\right) \cdot g \cdot m o {l}^{-} 1 \times n = 90.0 \cdot g \cdot m o {l}^{-} 1$.
Clearly $n$ $=$ $2$ and the molecular formula is $\left(H C {O}_{2}\right) \times 2$ $=$ ?? Is it oxalic acid?