Question

1)Sodium hydroxide cannot be used to prepare a primary standard titration solution because the compound is not available in high purity. The most common impurity is water because sodium hydroxide is hygroscopic meaning it absorbs water from the air. a)If sodium hydroxide that had aborbed water was used directly to prepare a standard solution how would the actual concentration differ from the presumed concentration? B)If this sodium hydroxide standard solution was used to titrate a hydrochloric acid solution of unknown concentration, how would the determined concentration compare to the actual concentration.   2)Explain why the titration curves in Fig 1, and presumably the ones constructed from the data obtained in this experiment, look very similar beyond the eqivalence point.     3) Explain why a ewak acid solution has a higher pH than a strong acid of the same concentratio.   4) Explain why the equivalence point of a weak acid titrated with a strong base occurs at a basic pH.

Answer 1

(a) Becuase it shows higher mass than the original mass of NaOH, so the resulting concentration would be represented more than the actual.

(b) Determined concentration of HCl would be than the actual concentration.

(3) Becuase weak acid does not undergo complete ionisation but strong acid undergoes complete ionisation. So, weak acid produces less amount of H⁺ ions than that of strong acid. So, the pH of weak acid is higher than the pH of strong acid.

((4) Because the slat obtained during the neutralisation of weak acid with strong base is in basic nature.