During a neutralisation reaction, a
student placed 25 cm3
of sodium
hydroxide in a flask and added
few drops of phenolphthalein.
The base required 22 cm3
of dilute hydrochloric acid for complete
neutralisation.
(a) What apparatus should have
been used to measure the exact
volume of sodium hydroxide
solution?
(b) What was the colour of the
solution at the end of the
neutralisation reaction?
(c) What reagent was more
concentrated than the other?
Explain.
(d) Name the salt that was formed.
(e) How would you obtain pure
crystals of the salt resulting from
the solution?
(a) A burette should have been used to measure the exact volume of sodium hydroxide solution.
(b) The colour of the solution at the end of the neutralisation reaction was likely pink, indicating that the phenolphthalein indicator was showing that the solution was slightly basic.
(c) The dilute hydrochloric acid was more concentrated than the sodium hydroxide solution. This is because it required less volume of hydrochloric acid to neutralize the sodium hydroxide solution.
(d) The salt formed from the neutralization reaction between sodium hydroxide and hydrochloric acid is sodium chloride.
(e) To obtain pure crystals of sodium chloride, the solution would need to be evaporated to dryness to crystallize the salt. The crystals can then be collected and washed with a small amount of ice-cold water to remove impurities.