Question

What is the molarity of a solution made using 2.19g of KI dissolved in enough water to make 266mL of solution.

Answer 1

Hint: We have to find the molarity of the solution. Molarity is defined as the no. of moles of solute in 1L of the solution. It is denoted by the symbol ‘M’ and is also known as the concentration of the solution.

Complete answer:
The formula for molarity of the solution can be given as: $ Molarity = \dfrac{{moles(solute)}}{{{V_{solution}}(L)}}mol/L $
Else it can also be given as: $ C = \dfrac{n}{V} $ , where C is the concentration (molarity), n is the no. of moles of solute and V is the volume of solution.
The units of molarity can be mol/L or $ mol/d{m^3} $ . V is the volume of the solution, in which the solute is dissolved. The information given to us is: Mass of solute = 2.19 grams, Volume of the solution = 266mL.
First, we’ll have to find the molar mass of KI to find the no. Of moles of KI Dissolved. The no. of moles of any substance is equal to $ moles = \dfrac{{Mass}}{{Molar{\text{ }}Mass}} $
The molar mass of KI = $ (39 + 127)g/mol = 166g/mol $
The no. of moles of KI $ = \dfrac{{2.19g}}{{166g/mol}} = 0.0132mol $
The volume of solution should be in Litres always, therefore volume of solution $ = 266mL = 0.266L $
Substituting the values in the formula for Molarity we get:
 $ M = \dfrac{{0.0132mol}}{{0.266L}} = 0.0496M $
The molarity of the solution is 0.0496 M.

Note:
The no. of moles has a SI unit of ‘mol’ , hence the mass and molar mass can be considered in Grams itself, instead of Kilograms (kg being the SI unit of mass). For molarity the Volume has to be considered in Litres or decimetres (dm) itself. If the volume given to us is in mL we’ll have to convert to L. The conversion terms are:
 $ 1L = 1d{m^3} = 1000mL $
 $ 1ml = {10^{ - 3}}L = {10^{ - 3}}d{m^3} $ .