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JAMB Chemistry 1997 Question 3

Question 3

Separation of Mixtures

Use the graph below to answer this question. A sample, X, solid at room temperature, was melted, heated to a temperature of 358 K and allowed to cool as shown in OPQR. The section PQ indicates that X is

Diagram for this question
  1. A.a mixture of salts
  2. B.a hydrated salt
  3. C.an ionic salt
  4. D.a pure compound
Show the answer and explanation

Answer: D (a pure compound)

Explanation

PQ is flat: the temperature stays constant while the liquid freezes. A sharp, fixed freezing point is a sign of a pure substance; a mixture freezes over a range of temperatures.