How can the concentration of a solution be expressed?
A solution has two components: the solute and the solvent. The concentration of a solution is the amount of solute present in a given amount of solution. Also, it can be defined as the amount of solute present in the given amount of solvent.
Let us understand two different ways of expressing it.
- Expressing concentration as a mass by mass percentage of a solution
Concentration of a solution can be expressed as a mass by mass percentage as follows:
𝑀𝑎𝑠𝑠 𝑏𝑦 𝑀𝑎𝑠𝑠 % 𝑜𝑓 𝑎 𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛 =𝑀𝑎𝑠𝑠 𝑜𝑓 𝑠𝑜𝑙𝑢𝑡𝑒 /𝑀𝑎𝑠𝑠 𝑜𝑓 𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛 × 100
- Expressing concentration as a mass by volume percentage of a solution Concentration of a solution can be expressed as a mass by volume percentage as follows:
𝑀𝑎𝑠𝑠 𝑏𝑦 𝑉𝑜𝑙𝑢𝑚𝑒 % 𝑜𝑓 𝑎 𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛 =𝑀𝑎𝑠𝑠 𝑜𝑓 𝑠𝑜𝑙𝑢𝑡𝑒 /𝑉𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛× 100
Both ways of expressing concentration of a solution are expressed in percentage. This is because percentage helps to comprehend it easily. For example, 30% concentration is not a lot, but 85% concentration is significant.
In both cases, the solution is the denominator and not the solvent.
Here’s a simple example to understand this.
A solution contains 20g of sugar in 230g of water. Let’s calculate the concentration in terms of
mass by mass percentage of the solution.
The mass of the solute is 20 grams, and that of the solvent is 230 grams. The mass of the solution is given by:
Mass of the Solution = Mass of the Solute + Mass of the Solvent
= 20g + 230g
= 250g
Now,
We get,
𝑀𝑎𝑠𝑠 𝑏𝑦 𝑀𝑎𝑠𝑠 % 𝑜𝑓 𝑎 𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛 =𝑀𝑎𝑠𝑠 𝑜𝑓 𝑠𝑜𝑙𝑢𝑡𝑒/𝑀𝑎𝑠𝑠 𝑜𝑓 𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛
20𝑔× 100
𝑀𝑎𝑠𝑠 𝑏𝑦 𝑀𝑎𝑠𝑠 % 𝑜𝑓 𝑎 𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛 =250𝑔/× 100 =8
Thus, the concentration of the solution is 8% in terms of mass by mass percentage.