In an experiment, 2.4 g of magnesium (Mr = 24) reacts completely with a sample of black solid copper(II) oxide (Mr = 80), according to Mg + CuO -> MgO + Cu. What mass of copper(II) oxide reacted?

A16 g

B4.0 g

C8 g

D6.4 g

Explanation

Moles Mg = 2.4/24 = 0.1; the 1:1 ratio in Mg + CuO -> MgO + Cu gives 0.1 mol CuO; mass = 0.1 x 80 = 8 g.

Derived from ZIMSEC Chemistry 5071/2 Paper 2 Theory, November 2013, Q3

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