Molarity: Ion Concentration

Question

In the laboratory you dissolve 20.3 g of barium acetate in a volumetric flask and add water to a total volume of 375 mL.

What is the molarity of the solution?   M.

What is the concentration of the barium cation?   M.

What is the concentration of the acetate anion?   M.

Answer 1

Hello, Nicole,

Molarity is defined as moles/liter. Determine the number of moles of barium acetate by dividing its mass by its molar mass, which I believe is around 255.5 g/mole. The division 20.3 g/255.5 g/mole will give the number of moles. If you put that into a liter, it would be the concentration in Molar. But you are only using 375ml, which is 0.375 liters. So divide the moles by 0.375 liter, and you'll have Molarity (moles/liter).

The formula is Ba(CH₃COO)₂. We have two acetate groups per molecule and only 1 for Ba. So the concentration of the barium ion is the same as the barium acetate molarity. But we get two acetates, so the acetate concentration is 2 times that of the barium acetate.

I hope this helps,

Bob