Question

What was the initial concentration of 100ml of KBr solution, if after adding water to dilute it, 300ml of a 4 percent solution was obtained?

Answer 1

Ans. Given, 300 mL of a 4% solution was obtained after dilution. It’s assumed that the given concentration is in terms of %(w/v), where, w= weight of solute (i.e. KBr) in 100 mL solution.

4% w/v solution means 4 gram KBr in 100 mL solution

Since, 100 mL solution contain 4 gram KBr

            Or, 1 mL            -           -    (4/ 100) gm KBr

            Or, 300 mL        -           -    (4/ 100) x 100 = 12 gram KBr.

Now, since only distilled water was added during dilution, the net weight (mass) of KBr in the solution remains the same in both the solutions (before and after dilution).

Thus, the amount of KBr in 100 mL (original) solution = 12 gram

Initial concentration (% w/v) = 12 gm KBr in 100 mL solution = 12 % w/v