CAIE IGCSE Chemistry Heating and Cooling Curves

Practise reading and sketching heating or cooling curves, locating melting, boiling and freezing points and explaining plateaux using particle attractions.

[Maximum number: 6]

2 Z is a covalent substance. In an experiment, a sample of pure solid Z was continually heated for 11 minutes.

The graph shows how the temperature of the sample of pure Z changed during the first 9 minutes.

Figure for Question 1.1.5—Changes of state using kinetic question 1 — CAIE IGCSE Chemistry

(a)

What is the melting point of pure Z ? ${ }^{\circ} \mathrm{C}[1]$

[ 1 ]

$80\left({ }^{\circ} \mathrm{C}\right)(1)$

(b)

The sample of pure Z began to boil at 9 minutes. It was boiled for 2 minutes.

Use this information to sketch on the grid how the temperature of the sample of pure Z changed between 9 minutes and 11 minutes.

[ 1 ]

(c)

The sample of pure Z was continually heated between 2 minutes and 5 minutes.

Explain, in terms of attractive forces, why there was no increase in the temperature of the sample of pure Z between 2 minutes and 5 minutes.

[ 2 ]

(d)

A sample of pure Z was allowed to cool from $120^{\circ} \mathrm{C}$ to $20^{\circ} \mathrm{C}$ . The total time taken was 8 minutes.

Starting from point x, sketch on the grid how the temperature of the sample of pure Z changed between 0 minutes and 8 minutes.

[Total: 10]

[ 2 ]

decrease from $120^{\circ} \mathrm{C}$ to $80^{\circ} \mathrm{C}$ and horizontal line at $80^{\circ} \mathrm{C}$ (1)

decrease from horizontal line to finish at $20^{\circ} \mathrm{C}$ at 8 mins (1)

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1.1.5—Changes of state using kinetic question 1

Question (a)

Question (b)

Question (c)

Question (d)