(i) What mass of anhydrous MgI2 is required to prepare a 400mL volume of 0.0250molL1 concentration?

(ii) Given 8.0molL1 HClO4(aq), what volume is required to prepare 4.00L of the acid at 0.250molL1 concentration?

1 Answer
Jun 5, 2017

Well, in both instances we use the relationship is:

Concentration=Moles of soluteVolume of solution

Explanation:

WE use the quotient to determine the number of moles of solute we need.......

i.e. if the solution is 0.0250molL1 with respect to MgI2, we needs a 400×103L×0.0250molL1=0.01mol quantity of the anhydrous salt.

And this represents a mass of 0.01mol×278.11gmol1=2.78g.

And to prepare this solution, we take an accurately measured mass of magnesium iodide (if your salt is the hydrate, we change the mass appropriately), and dissolve it up in a 400mL volume of water.

The second solution REQUIRES that we add the ACID to water and NOT WATER to ACID (important! so get it right!).

We require 4.00L×0.250molL1=1.0mol. And thus we START with 125mL of the 8.0molL1 solution of HClO4(aq), and we add this to a 3.875L volume of water.