Is muriatic acid a compound or not?

Hydrochloric acid is a mixture. Although we use HCl as the formula for hydrochloric acid, HCl is, in fact, the formula of hydrogen chloride, which is a compound. Hydrogen chloride is a gas which readily reacts with water.

HCl + H2O ———-> H3O^+(aq) and Cl^-(aq)

Hydrochloric acid is a mixture of these ions

H2O and H3O^+(aq) and Cl^-(aq)

There are many different concentrations of hydrochloric acid - it must be a mixture.

10.063g / 10.00 ml = 1.0063 g/ml which rounds off to 4 sig figs as: 1.006 g/ml