A metal carbonate containing an unknown +2 metal ("MCO3") reacts with excess acid resulting in the loss of CO2....

Question

A metal carbonate containing an unknown +2 metal ("MCO3") reacts with excess acid resulting in the loss of CO2. Analysis of the experimental data indicates that the mass % CO2in the unknown metal carbonate is 30%. Which of the metal cations below is most likely to be the unknown metal in the original metal carbonate?

A Ca

B Sr

C Pb or

D Cu (all 2+ charge)

Answer 1

MCO₃ + 2HX ==> MX₂ + H₂O + CO₂

Molar mass of CO₂ = 44 g/mole

44 g / molar mass of unknown = 0.30

molar mass of unknown = 44/0.30

molar mass of unknown = 147

MCO₃ = 147 and CO3 = 60 g/mol

Thus M = 147 - 60 = 87

This atomic weight is consistent with strontium or Sr, so answer appears to be (B) Sr²⁺