On combustion of 0.7 g of a monovalent metal in oxygen, 1.5 g of its oxide was formed

On combustion of 0.7 g of a monovalent metal in oxygen, 1.5 g of its oxide was formed. Define the period, group and subgroup of this element.

The molar mass of the metal is denoted by x. Let’s make a proportion.

4 Ме + O2 = 2 Ме2O.

4 x g / mol 2 (2x + 16)

4 x x 1.5 g = 0.7 x 2 (2 x + 16),

6 x = 0.7 × (4 x + 32)

6 x = 2.8 x + 22.4,

6 x – 2.8 x = 22.4

3.2 x = 22.4,

x = 22.4: 3.2,

x = 7.

M (Li) = 7 g / mol.

Answer: the metal is lithium.

It is in the II period, I – A – group (main subgroup).