Question

Calculate the mass of sodium acetate (\[C{H_3}COONa\]) required to make 500 mL of 0.375 molar aqueous solution. Molar mass of sodium acetate is 82.0245 \[g\,mo{l^{ - 1}}\].

Answer 1

Hint: The molarity of a solution is defined as the number of moles of solute in a solution divided by the total volume of the solution. Molarity is a concentration term and depends upon the volume of the solution.

Complete step by step answer:
Molarity of a solution is one way of expressing the concentration of the solute present in it. It is defined as the number of moles of solute per litre of solution. It is defined by M. In mathematical terms, it is expressed as:
Molarity (M) = $\dfrac{{Number\,of\,moles\,of\,solute}}{{Volume\,of\,the\,solution}}$
In order to calculate the molarity of a solution, you need to know the number of moles of solute and the total volume of the solution.
In the given question,
Molarity of solution = 0.375 M
Volume of solution = 500 mL = 0.5 L
Now,
0.375 = $\dfrac{{{n_{solute}}}}{{0.5}}$
$ \Rightarrow {n_{solute}}$ = $\dfrac{{0.375}}{2}$
$ \Rightarrow {n_{solute}}$ = 0.1875 moles
Therefore, mass of the solute = No. of moles x Molar mass
Mass of solute = 0.1875 x 82.0245 grams
Mass of solute = 15.38 g

Hence, the correct answer is 15.38 grams.

Note: Don’t confuse molarity of a solution with its molality. Molarity is equal to the ratio of number of moles and volume of solution while molality of a solution is equal to the moles of solute divided by the mass of solvent in kilograms.