dilutions

Dilution occurs when one solution is made weaker by the addition of more solvent (or by another solution).

It can be calculated using the mole as the base unit. Recall that molarity is moles per liter, so molarity multiplied by volume (in liters) yields moles.

So if you know molarity and volume, you can calculate moles; the number of moles of solute remains constant in a dilution. Only solvent (water, usually) is being modified. Therefore, dilutions can be calculated using the equation:

Mi x Vi = Mf x Vf

where i stands for initial solution, and f stands for final solution. Sometimes 1 and 2 are used in place of i and f, respectively.



Suppose a 1.5 M solution of sodium chloride is diluted to create 5.0 L of a 0.50 M solution.

Mf = 0.50 M Vf = 5.0 L

and

Mi = 1.5 M

Substitute into the dilution equation: (1.5 M) x Vi = (0.50 M) x (5.0 L) and solve for Vi.

Vi = 1.7 L, which means you need 1.7 L of the original 1.5 M NaCl solution, and you will add enough water to make 5.0 L.

Try the dilution calculator at the bottom of [|this link].