Question

What is the molarity if 3.5% $NaCl$ dissolved in $1000ml$ of distilled water?

Answer 1

Molarity is the number of moles of solute present in per liter of solution. In a mixture the component present in larger quantities is the solvent. Compounds mixed with the solvent are called solute. Together they form a solution.

Complete answer:
Molarity is the measure of concentration in a solution. It is measured as
Molarity $= \dfrac{{mol}}{L}$
Step $1$ : find the mass of each component
To find mass of the components we need to assume that the solution is of $1000gm$
Mass of $NaCl = 1000 \times \dfrac{{3.5g}}{{100g}}$
$= 35.0g$ of $NaCl$
Since $NaCl$ present in $1000gm$ is $35.0gm$ the mass of water will be $= 1000 - 35.0$ $= 965.0g$
Step 2: to calculate volume of the solution
Density is to be assumed as $1.023g/ml$
Volume of solution $= 1000g$ $\times \dfrac{{1ml}}{{1.023g}} = 977.5mL$
Step 3 : number of moles in $NaCl$
$= 35g \times \dfrac{1}{{58.44NaCl}}$
$= 0.599mol$
Number of moles of $NaCl$ present in the solution are $0.599$ $mol$ .
Step 4: Calculation of molar concentration of $NaCl$
$= \dfrac{{0.599mol}}{{0.9775L}}$ $= 0.61mol/L$
The unit of molarity is $mol/L$ or $M$ .
Molarity is the ratio of moles to volume. Volume of solvent can be measured by measuring its molarity. SI unit of molar concentration is $mol/{m^3}$ .

Note:
Morality is the measure of substance dissolved in a certain mass of solvent , it is different then molarity.. Same amount of moles of solute in two different solutions can be related by using the formula ${c_1}{V_1} = {c_2}{V_2}$ . $c$ is defined as the concentration and $V$ as the volume.