A group of students are standardising a sodium hydroxide solution, NaOH(aq)\text{NaOH(aq)}NaOH(aq), by titrating it against a 25.00 cm3 sample of a standard solution of potassium hydrogen phthalate (KHP\text{KHP}KHP) in a conical flask. The NaOH(aq)\text{NaOH(aq)}NaOH(aq) is delivered from a burette.
One student obtains a titre that is lower than the rest of the class.
Which of the following errors in technique explains this lower titre?
The pipette used to transfer the KHP\text{KHP}KHP solution was rinsed with distilled water but not with the KHP\text{KHP}KHP solution before filling.
The conical flask was rinsed with the KHP\text{KHP}KHP solution rather than distilled water before the titration.
The burette was rinsed with distilled water but not with the NaOH(aq)\text{NaOH(aq)}NaOH(aq) solution before filling.
An air bubble in the jet of the burette was displaced during the titration.
