Chemical reactions may be carried out with the aim of determining the composition of an unknown substance or with the aim of preparing a new compound. In either case, for the reaction to have a meaningful outcome, appropriate measurements must be made and calculations are required.
Each measurement is a number multiplied by a unit. The number is meaningless without the unit.
5 g means 5 times a standard mass that is called a gram.
50
means 50 times a standard volume that is referred to as a
.
This module will focus on accurate recording of measurements required in the preparation of a solution of exactly known concentration and on using these measurements in the calculations. Some of the relationships that you may use in these calculations are given below.
Concentration measures the
amount of solute (substance dissolved) in a
volume of solution.
Chemists commonly use concentration in
where amount is in moles (
n) and volume (
V) is in
. Thus the
concentration of the solution can be calculated by dividing the amount in moles of solute dissolved by the volume of
solution in
s.
required to make a solution of a certain volume depends on how the solute is added.
If solid solute is used, amount in moles is calculated by dividing the mass m in grams by the mass of one mole (molar mass M ) of solute.
If solute is added as a solution, amount in moles is calculated by multiplying the volume and concentration of the solution added.