You will need

- - the periodic system of chemical elements D. I. Mendeleev;
- calculator.

Instruction

1

In order to cope with the task, you need to use a formula to determine the relative density:

D (air) = Mr (gas)/ Mr (air) where:

D (air) – relative density;

Mr (gas) – relative molecular mass of a gaseous substance;

Mr (air) - relative molecular mass of air.

All three parameters units of measure do not have.

Mr (air) = 29 (a constant), hence the formula would be:

D (air) = Mr (gas)/ 29.

D (air) = Mr (gas)/ Mr (air) where:

D (air) – relative density;

Mr (gas) – relative molecular mass of a gaseous substance;

Mr (air) - relative molecular mass of air.

All three parameters units of measure do not have.

Mr (air) = 29 (a constant), hence the formula would be:

D (air) = Mr (gas)/ 29.

2

Similar is the formula to determine the relative density of hydrogen, with the exception that instead of air is hydrogen. And, therefore, no account is taken of the relative molecular mass of hydrogen.

D (hydrogen) = Mr (gas)/ Mr (of hydrogen);

D (hydrogen) is the relative density;

Mr (gas) – relative molecular mass of a gaseous substance;

Mr (hydrogen) is the relative molecular mass of hydrogen.

Mr (hydrogen) = 2, hence the formula would be:

D (air) = Mr (gas)/ 2.

D (hydrogen) = Mr (gas)/ Mr (of hydrogen);

D (hydrogen) is the relative density;

Mr (gas) – relative molecular mass of a gaseous substance;

Mr (hydrogen) is the relative molecular mass of hydrogen.

Mr (hydrogen) = 2, hence the formula would be:

D (air) = Mr (gas)/ 2.

3

Example No. 1. Calculate the relative density of ammonia in the air. Ammonia has the formula NH3.

First, find the relative molecular mass of ammonia, which can be calculated according to the table of D. I. Mendeleev.

Ar (N) = 14 Ar (H) = 3 x 1 = 3, hence

Mr (NH3) = 14 + 3 = 17

Substitute the data obtained in the formula for determination of relative density of air:

D (air) = Mr (ammonia)/ Mr (air);

D (air) = Mr (ammonia)/ 29;

D (air) = 17/ 29 = 0, 59.

First, find the relative molecular mass of ammonia, which can be calculated according to the table of D. I. Mendeleev.

Ar (N) = 14 Ar (H) = 3 x 1 = 3, hence

Mr (NH3) = 14 + 3 = 17

Substitute the data obtained in the formula for determination of relative density of air:

D (air) = Mr (ammonia)/ Mr (air);

D (air) = Mr (ammonia)/ 29;

D (air) = 17/ 29 = 0, 59.

4

Example No. 2. Calculate the relative density of ammonia by hydrogen.

Substitute the numbers into the formula to determine the relative density of hydrogen:

D (hydrogen) = Mr (ammonia)/ Mr (of hydrogen);

D (hydrogen) = Mr (ammonia)/ 2;

D (hydrogen) = 17/ 2 = 8, 5.

Substitute the numbers into the formula to determine the relative density of hydrogen:

D (hydrogen) = Mr (ammonia)/ Mr (of hydrogen);

D (hydrogen) = Mr (ammonia)/ 2;

D (hydrogen) = 17/ 2 = 8, 5.

# Advice 2: How to calculate density

**Density**is one of the characteristics of matter, such as mass, volume, temperature, area. It is the ratio of mass to volume. The main task is to learn how to calculate this value and know what it depends on.

Instruction

1

**The density**of a substance is numerically the ratio of mass to volume of a substance. If you want to determine the density of a substance and you know its mass and volume, finding the density will not make you work. The easiest way to find the density in this case is p = m/V. It is measured in kg/m^3 in SI units. However, not always a given these two values, so you should know some ways by which you can calculate the density.

2

**The density**has different values depending on the type of substance. In addition, the density changes from salinity and temperature. With decreasing temperature, the density increases, and with the lowering of the degree of salinity decreases and the density. For example, the density of the red sea is still considered high, and in the Baltic sea it is already less. All of you have noticed that if the water to fuel, it POPs up. All this is due to the fact that oil has a lower density than water. Metals and stone substances, on the contrary sink because their density is higher. On the basis of the density of bodies there was a theory about their swimming.

3

Thanks to the theory of the swimming of bodies there was a formula that I can find the density of a body, knowing the density of water, the volume of the body and the volume of its immersed part. This formula has the form:Vпогруж. part / V of the body = p / p liq.It follows that the density of the body can be found as follows:R body = V submersible. parts * fluid R / V body.This condition is satisfied on the basis of the tabular data and the given volume V submersible. part V of the body.