How much KCl do you need to use in order to make 275 ml of 2

How much KCl do you need to use in order to make 275 ml of 250 mM KCl? Answer should be in g.

Solution

A 1M solution is a solution in which 1 mole of a compound(molecular weight of compound) is dissolved in a total volume of 1 litre(1000 ml). Molecular weight of KCl is 74.55 g. To prepare 1 M KCl, 74.55 g of KCl should be added in 1000 ml of water (or any other appropriate diluent). So, for 1 M KCl (i.e. 1000mM KCl) = 74.55 g KCl is required to be added in 1000 ml of water. For 250 mM KCl = 18.64 g will be required (by cross multiplication, (250 mM x 74.55 g)/1000 mM) which will be in 1000 ml of water. Here, in this example, the total volume required is 275 ml. Therefore,for 250mM KCl = 18.64 g KCl in 1000 ml water For 250 mM KCl = 5.13 g KCl will be required to make it to 275 ml (by cross multiplication, (18.46 g x 275 ml)/1000 ml) 5.13 g KCl would be used in order to make 275 ml of 250 mM KCl.