Instruction

1

First, on the basis of a universal definition of density – the amount of substance per unit volume. In that case, if pure hydrogen is in a sealed vessel, the gas density is determined by the elementary formula (M1 – M2)/V, where M1 is the total mass of the vessel with the gas, M2 – mass of empty vessel, and V is the internal volume of the vessel.

2

If you want to determine the density

P – gas pressure

V is the volume

R – the universal gas constant

T is the gas temperature in degrees Kelvin

M – molar mass of gas

m – the actual weight of gas.

**of hydrogen**, with such initial data, as its temperature and pressure, then comes to the aid of the universal equation of state ideal gas law or the equation Mendeleev – Clapeyron: PV = mRT/M.P – gas pressure

V is the volume

R – the universal gas constant

T is the gas temperature in degrees Kelvin

M – molar mass of gas

m – the actual weight of gas.

3

An ideal gas is a mathematical model of gas in which the potential energy of interaction between molecules compared to their kinetic energy can be neglected. In the model of an ideal gas between the molecules are forces of attraction or repulsion and collision of the particles with other particles or vessel walls are absolutely elastic.

4

Of course, neither hydrogen nor another gas is not ideal, but this model allows calculating with high accuracy at conditions close to atmospheric pressure and room temperature. For example, given the task: find the density

**of hydrogen**at a pressure of 6 atmospheres and a temperature of 20 degrees Celsius.5

First, set all the initial value SI (6 atmospheres = 607950 PA, 20 degrees C=293 degrees K). Then write the equation Mendeleev-Clapeyron law PV = mRT/M. Convert it in the form: P = mRT/MV. Since m/V is density (the ratio of the mass of a substance to its volume), you get: the density

**of hydrogen**= PM/RT, where all the necessary data for the solution we have. You know the amount of pressure (607950), temperature (293), universal gas constant (8,31), the molar mass**of hydrogen**(0,002).6

Substituting these numbers into the formula you get: the density

**of hydrogen**under specified conditions of pressure and temperature is 0.499 kg/cubic meter, or about 0.5.# Advice 2 : How to find density chemistry

**Density**is one of the most important parameters of the physical body. According to the definition, density is a scalar value, which is measured for the homogeneous bodies as a ratio of body mass to its volume. There are several ways to learn the value of this parameter.

You will need

- - scales;
- - measuring Cup;
- - table volumes.

Instruction

1

Based on the definition, in order to know the density, you need to find the mass and volume of the body. This rule holds true for solids and liquids. Put the body on the scale and you will see the necessary quantitative indicators. Put the resulting value in pounds, which are the basic unit in the measurement system. If you know the mass of the liquid substance, before pouring it into the flask and weigh out the mass of the flask. You will need to take it away from the result.

2

If the body whose density you want to find is a regular geometric figure, you will be much easier. To find the volume of regular shapes, you can use the volumes table, find the formula and calculate the result. If the figure is wrong, take a measuring Cup and fill it with water (not completely). Write down what mark is water. Then lower the examined body in the water and mark the number where is the water now. The difference between second and first value will be the required volume. The liquid volume can also be measured using the same measuring Cup.

3

You only need to substitute the received data into the formula ρ = m/V where m is mass, and V is the volume of a material.

4

**The density of**gases is different. To do this you need to know the molar mass of the gas and its normal volume. If, according to the condition of the problem, the action takes place under normal conditions (temperature 0 C and pressure of 760 mm of mercury.St.), the normal volume is 22.4 l/mol. Molar mass is the mass of one mole of a substance. The formula for finding the density of gas is ρ = M/V norms.

5

If the temperature or pressure different from normal, to determine the density of the gas you have to use the formula of Clapeyron-Mendeleev and find the volume of gas: ρ* V = m/M * R*T, where ρ is the pressure, V the volume, m is the mass of gas, M – molar mass, T is the temperature in Kelvin and R is the universal gas constant, which is equal to 8.3 j/mol*K.