How can you make solution of 2M of 800 ml from 5M solution?

Answer 1

In order to have a 2M solution is means that you have 2 moles for every 1 liter. Because you only want to make 800mL of this solution you only need (0.8*2) moles of or 1.6 moles of the compound in your solution. This 1.6 moles is coming from your 5M solution. So how much 5M do you need to take out to have 1.6 moles. A 5 molar solution has 5 moles for every liter, since you only need 1.6 moles of it that you need(1.6/5) liters of the solution or 0.32 liters (320 mL).

Calculations done.

So your going to take 320 mL of the 5M solution and put it into an 800mL volumetric flask and add water up to the line, or to be more exact, add exactly 460 mL of water in order to dilute the solution from 5M to 800mL of 2M solution.