Question

10.5grams of zinc trioxocarbonate (iv)we're treated very strongly to a constant mass and the residue treated with excess hydrochloric acid. Calculate the mass of zinc chloride that would be obtained.

Answer 1

The International Union of Pure and Applied Chemistry (IUPAC) does not recognize the name you have given to ZnCO3. Zinc carbonate is a recognized by IUPAC.
ZnCO3 + heat --> ZnO + CO2, then
ZnO + 2HCl ==> ZnCl2 + H2O
mols ZnCO3 initially = g/molar mass = 10.5/125.4 = 0.0837
Then Convert to moles ZnCl2 formed this way:
0.0837 moles ZnCO3 x (1 mol ZnO/1 mol ZnCO3) x (1 mol ZnCl2/1 mol ZnO) = 0.0837 mols ZnCl2.
gramsZnCl2 = moles ZnCl2 x molar mass ZnCl2 = ? g