Copper powder is heated in an open crucible. The total mass of the crucible and its contents increases. Which statement is the best explanation for this?
Carbon dioxide from the burner is absorbed by the copper.
The copper melts and gains mass.
Copper reacts with oxygen to form solid copper(II) oxide.
Copper is reduced to copper(II) oxide.
55 exam-style questions on OCR GCSE Chemistry Introducing chemical reactions. Each one has a worked solution and a mark scheme showing where the marks go.