(3 pts) The stockroom prepared a solution by dissolving 0.2300 g of Erythrosin B (MW = 879.87 g/mol) in DI water in a 250.00 mL volumetric flask. A student pipetted 5 mL of the stockroom solution into a 100.00 mL volumetric flask and diluted it to the mark with DI water. The molar concentration of the stockroom's solution in the 250.00 mL flask is

Question

(3 pts) The stockroom prepared a solution by dissolving 0.2300 g of Erythrosin B (MW = 879.87 g/mol) in DI water in a 250.00 mL volumetric flask. A student pipetted 5 mL of the stockroom solution into a 100.00 mL volumetric flask and diluted it to the mark with DI water. The molar concentration of the stockroom's solution in the 250.00 mL flask is
.00105M. 
The molar concentration of the student's diluted solution in the 100.00 mL flask is ____M

If the student wishes to prepare 100.00 mL of a 4.50x10^-4M solution, she will need ____mL of the stockroom solution.

bobpursley · Answer

Hmmm.

You are given the Molarity of the stockroom solution. It is diluted by a factor of 20.

Molarity=Mstockroom/20

Now, for the second part

4.6E-4=Mstockroom/dilution factor
solve for dilution factor. Then, amount is equal to 100ml/dilution factor.

There are other ways of doing this. I will be happy to critique your work on the method you were taught.