Question

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

Answer 1

Hint: 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.