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I use a writing frame to take you through three separate back titrations, teaching you the 5 basic steps that are generally involved.
The first determines the percentage purity of a sample of Magnesium Oxide. The second determines the percentage of Calcium Carbonate in chalk. The third finds the concentration of Ammonia in a domestic cleaner.
Note that the result of a back titration will be inaccurate if chemical A is contaminated with a chemical that would also react with chemical B.