The table below shows results from a quality check on three white substances used in a sports-drink factory. Each substance was heated in a melting-point ap...
Question 1 Report
The table below shows results from a quality check on three white substances used in a sports-drink factory. Each substance was heated in a melting-point apparatus. A pure substance has a sharp melting point, whereas a mixture normally melts over a range of temperatures. One sample is sodium chloride, one is a salt solution that has dried incompletely, and one is pure glucose.
| sample | melting observation | melting temperature / degrees C |
|---|---|---|
| P | melts over a range | 132 to 138 |
| Q | sharp melting point | 146 |
| R | sharp melting point | 801 |
(a) Which sample is most likely to be a mixture? [1]
(b) Use Table 1 to give the melting temperature of pure glucose. [1]
(c) State why a melting range suggests that sample P is impure. [1]
(d) Give the name of the solvent in a salt solution. [1]
(e) Name a method that could be used to obtain sodium chloride crystals from a sodium chloride solution. [1]
Answer Details
(a) Sample P is most likely to be a mixture because it melts over a range. [1]
(b) Pure glucose has a melting temperature of \(146^\circ\mathrm{C}\). [1]
(c) A pure substance melts sharply at one temperature. Impurities cause melting over a range of temperatures, so P is impure. [1]
(d) The solvent in a salt solution is water. [1]
(e) Use crystallisation: evaporate some water and then allow the solution to cool so sodium chloride crystals form. [1]
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