. A 13 mL sample of a solution of AlBr3 was diluted with water to 56 mL. A 25 mL sample of the dilute solution was found to contain 2.21 M Br-. What was the concentration of AlBr3 in the original undiluted solution?

13 mL is diluted to 56 mL so everything in the original sample is now in 56 mL. If we take 25 mL of that and the M is 2.21M, the the amount in the 56 mL is 2.21M x (56 mL/25 mL) = ?