Question

100 ml of a solution containing 5g NaOH is mixed with 200 ml of M/5 NaOH solution . calculate the molarity of resulting solution?

Answer 1

initial volume of solution , V1 = 100mL

mass of NaOH = 5g

molar mass of NaOH = 40g/mol

so, number of mole of NaOH = 5/40 = 1/8 mol.

molarity of NaOH , M1 = number of mole of NaOH/volume of solution in L

= (1/8) × 1000/100 = 10/8 = 1.25 M

now we can say, 100mL of a solution of 1.25M NaOH is mixed with 200mL of M/5 NaOH solution.

so using formula, M1V1 + M2V2 = M(V1+V2)

where M is molarity of resulting solution.

so, 1.25 × 100 + 1/5 × 200 = M × (100 + 200)

or, 125 + 40 = M (300)

or, M = 165/300 = 0.55M

hence, molarity of resulting solution is 0.55M.