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Drop the base. An insoluble solid salt has the formula MgCOₓ⋅H₂O, where x is a whole number that can be determined by finding the relative formula mass of the salt. A crucible is placed on a balance and found to have a mass of 142.34 g. The salt is placed in the crucible, and the combined mass of the crucible and salt is 144.14 g. This mass of MgCOₓ⋅H₂O is placed in 150.0 cm³ of 0.240 mol dm⁻³ HCl and reacts completely.
The solution is diluted to 250 cm³ and 50.0 cm³, and the samples are titrated against 0.100 mol dm⁻³ NaOH, giving a mean titre of 20.08 cm³. Calculate the value of x.
A 200 cm³ solution contains a mixture of Ba(OH)₂ and NaOH. 250.0 cm³ H₂SO₄ with concentration 0.200 mol dm⁻³ is added so that H₂SO₄ is in excess of both reagents. The following reactions occur:
2NaOH(aq) + H₂SO₄(aq) → Na₂SO₄(aq) + 2H₂O(l)
Ba(OH)₂(aq) + H₂SO₄(aq) → BaSO₄(s) + 2H₂O
BaSO₄ is a precipitate and is removed by filtration. It is dried and weighed to have a mass of 3.05 g.
The remaining solution is made up to 500 cm³, and 50.0 cm³ samples are titrated with 0.100 mol dm⁻³ NaOH to find the remaining H₂SO₄, giving a mean titre of 41.30 cm³.
2NaOH + H₂SO₄ → Na₂SO₄ + 2H₂O
Calculate the concentration of NaOH in the 200 cm³ solution in mol dm⁻³.
