Solutions and Dilutions

Each mol of AlBr3 gives 3 mol of Br-.
Concentration of Br- in the diluted solution = 2.16 M
Concentraion of AlBr3 in the diluted solution = 2.16/3 = 0.72 M

Consider the concentration of AlBr3.
15 mL of solution was diluted to 56 mL.
Before dilution : M1 = ?, V1 = 15 mL
After dilution: M2 = 0.72 M , V2 = 56 mL
M1V1 = M2V2
M1 x 15 = 0.72 x 56
M1 = 0.72 x 56 / 15 = 2.688 M
Concentration of AlBr3 in the original undiluted solution = 2.688 M