Question

29.       You were trying to prepare 1.0 liter of a 1.0M solution of NaCl. By mistake you went over the desired final volume and the final volume of the solution was 1.2 liter. What is the actual concentration of the solution? The molecular weight of NaCl is 56 g/mol.

Answer 1

Molarity is defined as the concentraiton os solution which is expressed as number of moles of solute per liter of solution

So, to prepare 1 M NaCl solution 56 gms should be dissolved in 1 liter

But instead the volume of solvent used is 1.2 lit, the concentraion of solution is:

56 gms ---------> 1200 ml

x gms ------------> 1000 ml

Cross multiplication of the terms gives

1200 x Xgms = 56 x 1000

=> X gms = (56 x 1000)/ 1200

= 46. 667 gms of NaCl is present in 1000 ml of the solution of the given over run solution

If 56 gms -------> 1 Molar solution

46.667 gms -----> x molar solution

Cross multiplication of the terms:

x x 56 = 46.667 x 1

x = 46.667/ 56 = 0.833 M

Hence, the concentration of the given solution is 0.833 M

Alternate method:

We can use the formula M1V1 = M2V2

Here M1 = 1 M, V1 = 1000; M2 = x, V2 = 1200

1 X 1000 = x X 1200

x = 1000/ 1200 = 0.833 M

Hence, the molarity of the solution is 0.833 M