During the preparation and purification of a sample of benzoic acid, a student performs recrystallisation followed by filtration under reduced pressure and melting point analysis. Which of the following describes a correct experimental procedure or observation for these techniques?
The hot solution of benzoic acid should be cooled rapidly in an ice-water bath immediately after heating to ensure the formation of the largest possible, highly pure crystals.
During vacuum filtration using a Büchner funnel, the filter paper should be slightly larger than the funnel plate so that it folds up the sides to prevent any solid from escaping.
A Büchner flask is connected to a water pump to create a vacuum, which speeds up the filtration process and helps to dry the purified crystals on the filter paper.
To determine the melting point of the dry benzoic acid, the sample is heated rapidly at a rate of 10 ∘C min−110\text{ }^\circ\text{C min}^{-1}10 ∘C min−1 all the way through its expected melting range to get an accurate reading.
5 exam-style questions on OCR A A Level Chemistry Use of apparatus and techniques. Each one has a worked solution and a mark scheme showing where the marks go.