Define an element if the combination of hydrogen with this element having a valence of three contains 8.82% hydrogen.

Let us denote the unknown element by X. It is known that its valency is III. Then the formula will look like this: ХН3.

Let us find the mass fraction of the unknown element if it is known that 8.82% in the compound is hydrogen.

W (H) = 100% – 8.82% = 91.18%.

If the mass of hydrogen in the molecule is 3, and this is 8.82%, then the mass of the unknown element will be 91.18%.

Let’s make a proportion.

3 – 8.82%,

x – 91.18%.

Hence the mass of element X:

(3 × 91.18): 8.82 = 31.

According to the periodic table, we find the mass of the element. This is phosphorus.

Connection PH3.