Question

Unknown metal called M reacts with unknow halogen called X consists compound MX2.If we are heating this compound MX2 it happens reaction :2 MX2(k) > 2 MX(k) + X2(d).
When we are hating 1,12 g compound we get 0,720 compound MX and 56,0ml of gas.This reaction happened by normal conditions.
What is formula of metal M?
What is formula of Halogen X?

Answer 1

Unknown metal called M reacts with unknown halogen called X consists compound MX2. If we are heating this compound MX2 it happens reaction: $2\mathrm{MX2(k)} > 2\mathrm{MX(k)} + \mathrm{X2(d)}$.

When we are having 1,12 g compound we get 0,720 compound MX and 56,0 ml of gas. This reaction happened by normal conditions.

What is formula of metal M?

What is formula of Halogen X?

**Solution:**

Chemical reaction:

$$2 \mathrm{MX}_2(\mathrm{k}) > 2 \mathrm{MX}(\mathrm{k}) + \mathrm{X}_2(\mathrm{d}) \quad (1)$$ $$\mathrm{V}(\mathrm{X}_2) = 56.0\,\mathrm{ml}$$ $$\mathrm{n}(\mathrm{X}_2) = 56.0 \times 10^{-3} / 22.4 = 2.5 \times 10^{-3}\,\mathrm{mol}$$

from (1)

$$\mathrm{n}(\mathrm{M}) = \mathrm{n}(\mathrm{MX}_2) = 2 \mathrm{n}(\mathrm{X}_2) = 5.0 \times 10^{-3}\,\mathrm{mol}$$ $$\mathrm{m}(\mathrm{M}) = 1.12\,\mathrm{g}$$ $$\mathrm{Mr}(\mathrm{MX}_2) = \mathrm{m/n} = 1.12\,\mathrm{g} / 5.0 \times 10^{-3}\,\mathrm{mol} = 224\,\mathrm{g \cdot mol^{-1}}$$ $$\mathrm{Mr}(\mathrm{MX}) = \mathrm{m/n} = 0.720 / 0.005 = 144\,\mathrm{g \cdot mol^{-1}}$$ $$\mathrm{Mr}(\mathrm{X}) = \mathrm{Mr}(\mathrm{MX}_2) - \mathrm{Mr}(\mathrm{MX}) = 224 - 144 = 80\,\mathrm{g \cdot mol^{-1}}$$

So Unknown halogen is Br

$$\mathrm{Mr}(\mathrm{M}) = 224 - 2 \cdot \mathrm{Mr}(\mathrm{Br}) = 224 - 180 = 64\,\mathrm{g \cdot mol^{-1}}$$

So unknown metal is Cu

Unknown compound CuBr2

**Answer:** Cu and Br.