Making soluble salts (except sodium, potassium and ammonium salts)
5 marks · HardA student prepares hydrated magnesium sulfate crystals by reacting magnesium carbonate with dilute sulfuric acid.
Write the balanced symbol equation for the reaction between magnesium carbonate and dilute sulfuric acid.
State the state symbols for each product.
During the process, the solution is concentrated and then left to crystallise. Write the equation for the crystallisation step, including water of crystallisation.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) \ce{MgCO3(s) + H2SO4(aq) -> MgSO4(aq) + CO2(g) + H2O(l)}
(b) MgSO4(aq): aqueous, CO2(g): gas, H2O(l): liquid
(c) \ce{MgSO4(aq) + 7H2O(l) -> MgSO4.7H2O(s)}
Must show: balanced symbol equation for part a, correct state symbols for part b, hydrated salt equation for part c
Also accept: Fully correct alternative hydrated formula (different notation, e.g., MgSO4.7H2O instead of MgSO43H2O accepted)
Common mistakes: Unbalanced equation in (a); Missing water as a product in (a); Omission of correct state symbols; Missing water of crystallisation in (c)
Show mark scheme and worked solution
Marking points
A1 (a) · 1 mark · MgCO3 and H2SO4 as correct reactants, using appropriate formulas.
A2 (a) · 1 mark · Balanced equation with correct products: MgSO4(aq) + CO2(g) + H2O(l).
B1 (b) · 1 mark · Correct state symbols for all three products (aq, g, l).
C1 (c) · 1 mark · Shows water of crystallisation is included (uses 7H2O).
C2 (c) · 1 mark · Balanced crystallisation step: \ce{MgSO4(aq) + 7H2O(l) -> MgSO4.7H2O(s)}.
Worked solution
(a) The balanced symbol equation is:
(b) The state symbols for the products are:
MgSO4(aq) (aqueous), CO2(g) (gas), H2O(l) (liquid)
(c) The equation for the crystallisation step is: