Question
OCR J258/02 — Higher tier
The heating curve below shows temperature vs time for a substance being heated from −20 °C to 120 °C (assume standard solid → liquid → gas heating curve shape).
(a) Explain why the temperature remains constant during the flat sections of the heating curve, even though energy is still being supplied. (3 marks)
(b) The substance has a melting point of 20 °C and a boiling point of 85 °C. Identify the state(s) present at 50 °C. Explain your answer. (2 marks)
(c) Suggest how the graph would change if a small amount of soluble impurity was added to the substance. (2 marks)
7 marks · take your time before peeking.
Sign up to try the next 30 problems
Save your streak, mark answers against the spec, and build a daily revision habit. Free during public beta — no card, no auto-renew.
Generated by TopMyGrade AI · cross-check official sources before relying on the mark-scheme phrasing.