Question: why is mgco3 insoluble in water?
Answer: Magnesium carbonate is sparingly soluble in water (0.02 g per 100 g water at RT) because its lattice energy is reasonably high. ... Thus, the larger the lattice energy, the more difficult it is for an ionic compound to dissolve in water. In the case of MgCO3, this value becomes more than 3,000 kJ/mol.