Determine the formula of a substance if the mass fraction of nitrogen in them is 82%, and hydrogen is 18%.

Decision:

1. Let’s designate: x – molecular weight of a substance, a – number of nitrogen atoms, b – number of hydrogen atoms.

2. The relative atomic mass of nitrogen is 14, hydrogen is 1.

3. Let’s compose the following expressions:

0.82 = 14 * a / x;

0.18 = b / x;

1. Let’s express the molecular weight:

x = 14 * a / 0.82 = 17a;

x = b / 0.18 = 5.556b;

1. Let’s equate the obtained expressions: 17a = 5,556b.

The most suitable are the following values: a = 1, b = 3. The unknown substance is ammonia, its formula is NH3.

Answer: the formula of the substance is NH3.