Question

4.9 grams of ${{H}_{2}}S{{O}_{4}}$ is mixed with water to form 5 litres of aqueous solution. Find its concentration (molecular weight of sulphuric acid is 98gm/mole).

Answer 1

Hint: We can calculate the concentration of a solution in terms of molarity. If we find the number of moles of the solute, we can put it in the formula of molarity and it will give us the concentration of solution in ‘molar’ or ‘M’.
Molarity=$\dfrac{number\text{ }of\text{ }moles\text{ }of\text{ }solute}{litres\text{ }of\text{ }solvent}$

Complete step-by-step answer:
As we know, concentration of a solution is the measure of amount of solute dissolved in a solvent to form a solution. The most common unit for calculation of concentration is molarity.
Molarity of a solution is the number of moles of solute per litres of the solvent.
Therefore, higher value of molarity means the solution is concentrated and lower value of molarity means the solution is dilute.
We can calculate concentration either by mass, by volume or by molarity.
As we discussed above, concentration is the measure of the amount of solute dissolved in a solvent, here we have 4.9 grams of sulphuric acid which is the solute mixed in 5 litres of water which is the solvent.
To calculate the number of moles of the solute, we can divide the mass of the solute used by its gram molecular weight.
Here, we have 4.9 grams of sulphuric acid and molecular weight of sulphuric acid is given to us which is 98gm/mole.
Therefore, the number of moles of sulphuric acid = $\dfrac{4.9}{98}$= 0.05 moles.
We know, molarity = $\dfrac{number\text{ }of\text{ }moles\text{ }of\text{ }solute}{litres\text{ }of\text{ }solvent}$
Here, we have 0.05 moles of solute in 5 litres of solvent.
Therefore, molarity =$\dfrac{0.05}{5}=0.01$
Therefore, the concentration of the solution is 0.01M.
We can also write this in terms of normality as,
Normality = molarity$\times $number of hydrogen ions.
Sulphuric acid is dibasic acid as it has two hydrogen ions.
Therefore, normality=$0.01\times 2=0.02N$
Therefore the concentration of the solution is 0.01M or 0.02N.

Note: We should not get confused between normality and molarity. Normality is the gram equivalent weight of solute per litres of solvent and molarity is the number of moles of solute per litres of solvent. Molarity is the molar concentration which is the most common unit for calculation of concentration.