How to calculate molar and normal concentration

How to calculate molar and normal concentration

Understand the size characterizing a share of the substance which is in any certain volume or mass of solution as the term "concentration". The more this share, the concentration is higher. It can be expressed through various indicators: mass fraction, molarity, molyalnost, normality, caption. Molar concentration – the size showing how many moths of this substance are in one liter of solution.


1. Let's say you know that 500 milliliters of solution of sulfuric acid contain 49 grams of this substance. Question: what molar concentration of this solution? Write down an exact formula of substance – H2SO4 then count its molecular weight. It consists of atomic masses of elements, taking into account their indexes. 1*2 + 32 + 4*16 = 98 atomic units of mass.

2. The molar mass of any substance is in number equal to its molecular weight, is only expressed in grams/mol. Therefore, one mol chamoisof acids weighs 98 grams. How many moths the initial amount of acid, to equal 49 grams is? Divide: 49/98 = 0.5.

3. Therefore, 0.5 moths of sulfuric acid contain in 500 milliliters of solution. How many moths would be in 1 liter? Certainly, one. Means, you have one-molar solution of sulfuric acid. Or, as it is accepted to write down, 1M solution.

4. And what is normal concentration? It is the size showing how many equivalents of substance (that is such number of his moths which reacts with one moths of hydrogen) contain in one liter of solution. Dimension of normal concentration - mol-ekv/l or g-ekv/l. It is designated by the letters "N" or "N".

5. Review an example with the same sulfuric acid. You already calculated that its solution one-molar. And what will be its normal concentration? For the answer to this question you need to consider that according to the law of equivalents, all substances react with each other in equivalent ratios. Thus, the size of normality of solution of sulfuric acid depends on what reaction with what substance she will enter.

6. For example, H2SO4 + NaOH = NaHSO4 + H2O. In this reaction to each molecule of a caustic natr also one molecule of sulfuric acid is the share (or of one equivalent of alkali – one equivalent of acid). Therefore, in this case acid solution one-normal (1N or just N).

7. But if alkali is taken much, then reaction will leak so: H2SO4 + 2NaOH = Na2SO4 + 2H2O. And then, as two molecules of alkali are already the share of each molecule of acid, solution of acid will be two-normal (2N).

Author: «MirrorInfo» Dream Team