A quality-control chemist checks a bottle labelled sodium hydroxide solution. Fig. 1 shows the titration apparatus used. A measured volume of the alkali is ...
Question 1 Report
A quality-control chemist checks a bottle labelled sodium hydroxide solution. Fig. 1 shows the titration apparatus used. A measured volume of the alkali is placed in a conical flask with a few drops of methyl orange. Hydrochloric acid is run from the burette into the flask while the solution is swirled. The colour changes from yellow to orange at the end-point. The chemist repeats the reaction until concordant readings are obtained. Sodium chloride solution is produced in this neutralisation.
(a) Name the piece of apparatus used to deliver an accurate fixed volume of sodium hydroxide solution into the flask. [1]
(b) State the colour of methyl orange in the conical flask before hydrochloric acid is added. [1]
(c) Explain why the chemist repeats the titration. [2]
(d) Complete the ionic equation for this reaction.
H+(aq) + OH−(aq) → ............ [2]
Answer Details
(a) A pipette delivers an accurate fixed volume of sodium hydroxide solution. [1]
(b) Methyl orange is yellow in the alkaline sodium hydroxide solution before acid is added. [1]
(c) Repeating the titration allows concordant, consistent results to be obtained. A reliable mean titre can then be calculated, reducing the effect of random error. [2]
(d) Hydrogen ions from the acid react with hydroxide ions from the alkali to form water:
\[\mathrm{H^+(aq)+OH^-(aq)\rightarrow H_2O(l)}\] [2]
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