Question

Metal carbonates decompose to the metal oxide and CO2 on heating according to this general equation. Mx(CO3)is) → My(s) + yCO2(g) You heat 0.0900 g of a white, solid carbonate of a Group 2A metal and find that the evolved CO2 has a pressure of 69.8 mm Hg in a 285 mL flask at 25 °C. Determine the molar mass of the metal carbonate.

Answer 1

84.11 g/mol

Step-by-step explanation:

A metal from group 2A will form the cation M²⁺, and the ion carbonate is CO₃²⁻, so the metal carbonate must be: MCO₃, and the reaction:

MCO₃(s) → MO(s) + CO₂(g)

For the stoichiometry of the reaction, 1 mol of MCO₃(s) will produce 1 mol of CO₂. Using the ideal gas law, it's possible to calculate the number of moles of CO₂:

PV = nRT , where P is the pressure, V is the volume(0.285 L), R is the gas constant (62.36 mmHg*L/mol*K), n is the number of moles, and T is the temperature (25 + 273 = 298 K).

69.8*0.285 = n*62.36*298

18583.28n = 19.893

n = 0.00107 mol

So, the number of moles of the metal carbonate is 0.00107. The molar mass is the mass divided by the number of moles:

0.0900/0.00107 = 84.11 g/mol