The properties of oxides

2 marks · Easy

When 1.6 g of phosphorus is burned in excess oxygen, phosphorus(V) oxide ( ) is formed as a white solid.

Calculate the mass of oxygen that reacts (Ar: P = 31, O = 16), and state whether phosphorus(V) oxide is acidic or basic.

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Mass of oxygen that reacts = 1.0 g; phosphorus(V) oxide is an acidic oxide.

Also accept: 1.03 g oxygen; P4O10 is acidic; phosphorus(V) oxide is acidic

Common mistakes: Incorrect calculation of oxygen mass; Stating phosphorus oxide is basic

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Marking points

M1 · 1 mark · Correct calculation of mass of oxygen that reacts (with correct steps and use of atomic masses).

A1 · 1 mark · Correctly stating that phosphorus(V) oxide is an acidic oxide.

Worked solution

Balanced equation: 4P + 5O2 → P4O10

Mass ratio: 4 × 31 g of P reacts with 5 × 32 g of O2.

Total P: 124 g; total O2: 160 g

For 1.6 g P: oxygen needed =

But the mass of O (not O2) in the product is:

Phosphorus(V) oxide is an acidic oxide.