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The percentage purity of powdered, impure magnesium sulfate, MgSO₄, can be determined by gravimetric analysis - VCE - SSCE Chemistry - Question 1 - 2008 - Paper 1
Question 1
The percentage purity of powdered, impure magnesium sulfate, MgSO₄, can be determined by gravimetric analysis. Shown below is the method used in one such analysis. ... show full transcript
Worked Solution & Example Answer:The percentage purity of powdered, impure magnesium sulfate, MgSO₄, can be determined by gravimetric analysis - VCE - SSCE Chemistry - Question 1 - 2008 - Paper 1
Step 1
Different volumes of 0.100 M BaCl₂(aq) are added to six separate 20.00 mL samples of this solution.
Answer
To determine the percentage purity of MgSO₄, measure the volume of 0.100 M BaCl₂ used for each 20.00 mL sample. Each volume added should lead to the precipitation of a corresponding mass of BaSO₄. The mass of BaSO₄ can be calculated from its relation with the original sulfate concentration.
Step 2
The equation for the reaction is Ba²⁺(aq) + SO₄²⁻(aq) → BaSO₄(s)
Answer
Using stoichiometry, relate the moles of BaSO₄ precipitated back to the moles of MgSO₄ in the original solution. For example, if 2.00 g of BaSO₄ precipitate is recovered, convert this mass to moles:
Since the reaction is 1:1, this also represents the moles of SO₄²⁻ precipitated, which in turn equals the moles of MgSO₄ in the initial sample.
Step 3
The precipitate from each sample is filtered, rinsed with de-ionised water and then dried to constant mass.
Answer
Calculate the concentration of the original MgSO₄ solution based on the total volume and concentration of BaCl₂ added. Finally, to find the percentage purity, use the formula: