Instruction

1

The key formula for the density is ρ=m/V where ρ is the density, m is the mass of the solution, V is the volume. Density can be expressed, for example, in kilograms per liter or grams per milliliter. In any case, it shows how much the mass of a substance per unit volume.

2

The mass of solution is mass of liquid and mass of dissolved substances: m(solution)=m(liquid)+m(solute). The mass of solute and volume of solution can be found from the known values of concentration and molar mass.

3

For example, in the problem given molar concentration of the solution. It is denoted by the chemical formula of the compound in square brackets. So, entry [KOH]=15 mol/l means that in one liter of solution contains 15 mole of potassium hydroxide.

4

Molar mass of KOH is 39+16+1=56 g/mol. Molar masses of elements in the periodic table, they are usually below the item name. The amount of substance, mass of a substance and its molar mass are related by ν=m/M where ν is the amount of substance (mol), m is the mass (g) M – molar mass (g/mol).

5

The solutions, in addition to the liquid, there are also gas. In this case, you need to understand that equal volumes of gas close to ideal, under the same conditions contains the same number of moles. For example, under normal conditions one mole of any gas occupies a volume of Vm=22.4 l/mol, which is called molar volume.

6

In a gas the density of the solution may need a ratio that establishes the relationship between amount of substance and volume: ν=V/Vm where ν – quantity of the substance, V is the solution volume, Vm is the molar volume, a constant value for the given conditions. As a rule, in such problems is discussed that the conditions are normal (n.).

# Advice 2 : How to determine the density of the liquid

The fluid density is a physical quantity that shows the mass of the fluid per unit volume. The density of the fluid can be measured as an indirect method, and direct measurements with the help of special devices.

You will need

- measuring Cup or beaker, scale, ruler, hydrometer.

Instruction

1

So, you have a liquid the density of which is going to determine. Take the empty measuring Cup or beaker, place it on the scale and determine the mass of the empty vessel with no fluid. Label it m1, for example. Then pour into this vessel the liquid whose density you want to measure. Pour the liquid to such a level that it was easy to determine its volume (in a small measuring cups marked scale of volume in milliliters).

2

After you have determined and recorded the volume of fluid (V), again place the container on the scale, just now it will be liquid. Record the new mass and label it m2. Knowing the mass of the empty dish m1 and complete m2 of the vessel, determine the mass of the liquid m by the formula: m = m2 – m1. Now you can go directly to the definition of the density Rho:

ro = m / V,

where m and V – mass and volume of the fluid found above.

ro = m / V,

where m and V – mass and volume of the fluid found above.

3

Remember that the liquid volume is usually measured in kilograms per cubic meter or in grams per cubic centimeter. Therefore, translating the measured values to one or second standard system of units of measurement. For example:

1 milliliter = 1 cubic centimeter

1000 liters = 1 cubic meter

1 kilogram = 1000 grams

1 milliliter = 1 cubic centimeter

1000 liters = 1 cubic meter

1 kilogram = 1000 grams

4

If a vessel with the liquid is large enough, but you know the mass of the empty dish, and m1 the mass of the filled vessel m2, it is possible to do the following. First, find the mass of liquid in the vessel by the formula m = m2 – m1. Then use a ruler or measuring tape, measure the geometric dimensions of the vessel: for rectangular vessels measure the height, width and length, for cylindrical – diameter and height. For finding the volume of a rectangular vessel, use the formula:

V = a * b * h

where a is width, b – length, h – height of the vessel.

V = a * b * h

where a is width, b – length, h – height of the vessel.

5

To find the volume of the cylindrical vessel, take the following formula:

V = (pi * d * d * h) / 4,

where pi is the number PI = 3.14, d is the vessel diameter, h is its height (the height of the liquid level).

After finding volume find the density of the liquid, as in the previous case, by the formula Rho = m / V.

V = (pi * d * d * h) / 4,

where pi is the number PI = 3.14, d is the vessel diameter, h is its height (the height of the liquid level).

After finding volume find the density of the liquid, as in the previous case, by the formula Rho = m / V.

6

The problem of determining the density is much easier if you have a hydrometer. This device is a glass tube with float and scale. Just dip it in the liquid so that it does not touch the bottom, and on a scale at the top of the hydrometer will see the density of the liquid. Often motorists use hydrometer to determine the density of the electrolyte in the battery.