After performing a dilution calculation, you determine you need 25.0 milliliters of an aqueous stock solution to make 100.0 milliliters of a new solution. How would this be prepared?

1 Answer
Aug 17, 2016

Answer:

Here's what I got.

Explanation:

You know that you need #"25.0 mL"# of a stock solution to make #"100.0 mL"# of a new, diluted solution. This basically means that you're going to dilute your stock solution by a factor of

#(100.0color(red)(cancel(color(black)("mL"))))/(25.0color(red)(cancel(color(black)("mL")))) = 4#

You thus know that for every #4# parts of this new, diluted solution, #1# part is accounted for by the stock solution and #3# parts are accounted for by water, you diluent.

The trick now is to realize that despite the fact that you'd need

#"100.0 mL " - " 25.0 mL" = "75.0 mL"#

of water to make this new solution, you should not add exactly #"75.0 mL"# of water to your #"25.0 mL"# of stock solution. Instead, you should add enough water to make sure that the total volume of the solution is equal to #"100.0 mL"#.

So, to prepare this solution, you should add #"25.0 mL"# of stock solution to a volumetric flask, then add water until the total volume is equal to #"100.0 mL"#. You just diluted your stock solution by a factor of #4#.