Question

For preparing \[0.1\text{ }M\]solution of \[{{H}_{2}}S{{O}_{4}}\] in one litre, we need \[{{H}_{2}}S{{O}_{4}}:\]
A.\[9.8\text{ }g\]
B.\[4.9\text{ }g\]
C.\[49.0\text{ }g\]
D.\[0.98\text{ }g\]

Answer 1

Hint: We know that the molarity (M) determines the number of moles of solute per litre of solution which is denoted as moles/Liter and is amongst the most common units that are used for measuring the concentration of a solution. Molarity is used for the calculation of the volume of the solvent or the amount of solute.

Complete answer:
Molarity, molality, and normality are all units of concentration. Molarity is defined as the number of moles of solute per liter of solution. Molality is defined as the number of moles of solute per kilogram of solvent and Normality is defined as the number of equivalents per liter of solution. We should use Molality instead of Molarity in experiments involving significant temperature changes. This is because as the volume of a solution increases with temperature, heating causes molarity to decrease; however, since molality is based on mass rather than volume, molality remains unchanged.
For calculating the molarity of a solution, the number of moles of solute should be divided by the total litres of the solution that is produced. If the amount of solute is given in grams, you must first calculate the number of moles of solute by using the molar mass of the solute and then calculate the molarity by using the number of moles and the total volume. First we have to calculate the number of moles in the solution. We can use the following equation to find it.
\[Molarity=\dfrac{Given\text{ }mass\text{ }of\text{ }compound}{Molar\text{ }mass\text{ }of\text{ }compound}\times Volume\text{ }of\text{ }solution\text{ }in\text{ }L\]
Here we have, Molar mass of \[{{H}_{2}}S{{O}_{4}}=98\text{ }g/mol\] and volume of solution \[=1L.\]
\[0.1M=\dfrac{Given\text{ }mass\text{ }of\text{ }compounds}{98\text{ }g/mol}\times 1L.\]
Thus, the given mass of compound \[=9.8g.\]
Therefore, the correct answer is option A.

Note:
Remember that the molar concentration can be used to convert between the mass or moles of solute and the volume of the solution. Molarity is a measurement of the moles in the total volume of the solution, whereas Molality is a measurement of the moles in relationship to the mass of the solvent. Hence, the two should never be confused.