The properties of oxides

2 marks · Easy

A student burns 2.0 g of sodium in oxygen to form sodium oxide ( ). Sodium oxide is then added to water, and a solution forms that turns universal indicator blue.

Calculate the mass of sodium oxide formed (using Ar: Na = 23, O = 16), and state whether sodium oxide is an acidic or basic oxide.

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Mass of Na2O formed = 2.7 g (to 2 significant figures, working shown); sodium oxide is a basic oxide.

Also accept: Sodium oxide is basic; 2.74 g; Na2O is a basic oxide

Common mistakes: Stating sodium oxide is acidic; Incorrect relative formula mass calculation; No explanation given

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Marking points

M1 · 1 mark · Correct calculation of the mass of sodium oxide formed (using correct formula masses and step shown).

A1 · 1 mark · Correctly stating that sodium oxide is a basic oxide.

Worked solution

Relative formula mass of Na2O = (2 × 23) + 16 = 62.

2Na (2 × 23 g = 46 g) produce 62 g of Na2O.

Therefore, 2.0 g Na produces:

Sodium oxide is a basic oxide as it forms an alkaline solution in water.