Question

first task is to prepare 250 ml of 3 M glucose. Then You are preparing a solution and the recipe calls for 25 ml of 10% glucose. How much of the 3M glucose stock would you need to add to so that you are adding the same molar amount of glucose?

Answer 1

You make 3M glucose with 135 g glucose in 250 mL soln. (Check it: That is (135/180) x (1/0.250) = 3 M

25 mL of a 10% soln is how many grams. That is 10g x (25/100) = 2.5 g glucose.

So the question is how much of the 3M stuff to take to obtain 2.5g. That is
250 mL x (2.5/135) = 4.62 mL.
Check my work.