# How many grams of KNO_3 (molar mass = 101.103 g/mol) should be used to make 325.0 ml of 0.070 M...

## Question:

How many grams of {eq}KNO_3 {/eq} (molar mass = 101.103 g/mol) should be used to make 325.0 ml of 0.070 M solution?

## Molarity:

The concentration of a solute in a solvent is generally expressed using the unit molarity (M). It is defined as the number of moles of the solute present in 1 liter of the solution.

{eq}M =\displaystyle \frac{n}{V} {/eq}

• n is the number in moles of solute
• V is the volume of the solution in L.

Given:

• The concentration of the solution is M =0.07 M.
• The volume of the solution is V = 325.0 mL = 0.325 L.

Number of moles in the solution is given by

{eq}n = MV = 0.07 \times 0.325 \ moles = 0.02275 \ moles {/eq}

The molar mass of {eq}KNO_3 {/eq} is {eq}M = 101.103 \ g/mol. {/eq}

The total amount of {eq}KNO_3 {/eq} needed is given by

{eq}\begin{align*} m& = n.M \\ & = 0.02275 \times 101.103 \ g \\ & = 2.3 \ g\Rightarrow(Answer) \end{align*} {/eq}