8.1 Define an acid in terms of the Lowry-Brønsted theory. (2)
8.2 Consider the following acid-base reaction:
H2PO4+ NH3 → HPO42- + NH4+
8.2.1 Identify the conjugate acid-base pairs in the above reaction. (4)
8.2.2 Define the term ampholyte. (1)
8.2.3 Choose an ampholyte in the above reaction. (2)
8.3 Ten grams (10 g) of an impure sample of sodium carbonate is added
to 100 cm3 of a 0,2 mol.dm-3 solution of hydrochloric acid. The acid is
in excess.
The equation for the reaction is:
Na2CO3 + HCℓ → NaCℓ + H2O + CO2
8.3.1 Balance the equation above. (1)
8.3.2 Calculate the number of moles of hydrochloric acid. (3)
The excess acid neutralises 20 cm3 of a solution of 0,1 mol.dm-3 of
magnesium hydroxide.
2HCℓ(aq) + Mg(OH)2(aq) → MgCℓ2(aq) + H2O(ℓ)
8.3.3 Calculate the percentage purity of the sodium carbonate solution. (8)
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