The energy involved in change of state
3 marks · EasyA student wants to demonstrate how the temperature of stearic acid (a solid) changes as it melts and then becomes a liquid.
Describe one safety precaution the student should take while heating stearic acid.
Explain what happens to the temperature of stearic acid as it is heated, melts, and then is fully in liquid form.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) Use a water bath, not a direct flame, to heat it.
(b) Temperature rises before melting, remains constant during melting, and rises again when it is fully liquid.
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Suggests appropriate safety precaution (e.g. heat indirectly, avoid skin contact, or use safety glasses).
B2 (b) · 1 mark · Mentions temperature rises before melting and after melting.
B3 (b) · 1 mark · Mentions temperature remains constant during melting.
Worked solution
a) The student should use a water bath to gently heat stearic acid, not a direct flame (to avoid fire risk). b) As stearic acid is heated, temperature increases until it reaches its melting point. During melting, the temperature remains constant. After all has melted, the temperature rises again if heating continues.