Question

You need to prepare a 2.30 M solution of sodium nitrate (molar mass of sodium nitrate = 84.99 g/mol) but you only have a 10 mL graduated cylinder and a 25 mL beaker. Complete the following sentences regarding the concentration of the prepared solution.

Answer 1

Step 1 - Understanding molarity

The molarity of a solution can be calculated by the following formula, which is precisely the definition of molarity:

$\lbrack NaNO_3\rbrack=\frac{m}{M\times V}$

In this equation, m represents the mass, M the molar mass and V the volume. We can use this formula to solve the exercise.

Step 2 - Finding the required mass of NaNO3

We want the molarity to be 2.3 M (mol/L). We know the molar mass is 84.99 g/mol and the volume is 0.01 L. Substituting these values in the equation above:

$m=\lbrack\text{NaNO}_3\rbrack\times M\times V=2.3\times84.99\times0.01=1.95\text{ g}$

The mass of NaNO3 we would need is thus 1.95 g.

Step 3 - Finding the final volume of the solution

The final volume of the solution will be:

$V_{\text{ final}}=V_{solvent}+V_{solute}$

Since Vsolvent = 10 ml, and we also need to add the volume of the solute, the final volume will be thus greater than 10 ml.

Step 4 - Finding the concentration of the solution

Since we used exactly the mass and the volume we needed to prepare a solution 2.3 M of KNO3, the molatiry of the solution will be exactly 2.3 M.