Why does the dilution equation, m 1 v 1 = m 2 v 2, work? a) the dilution equation works because the mass remains the same. b) the dilution equation works because the molarity remains the same. c) the dilution equation works because the volume remains the same. d) the dilution equation works because the number of moles remains the same.

d) The dilution equation works because the number of moles remains the same.

Explanation:

Let’s say that you have 1 mol of a solute in I L of solution. The concentration is 1 mol·L⁻¹. and M₁V₁ = 1 mol.

Now, you dilute the solution to a volume of 2 L. You still have 1 mol of solute, but in 2 L of solution. The new concentration is 0.5 mol·L⁻¹.

The volume has doubled, but the volume has halved, and M₂V₂ = 1 mol.

b) Wrong. The molar concentration changes on dilution.

c) Wrong. The volume changes on dilution.

a) Wrong, although technically correct, because if the moles don’t change, the mass doesn’t change either. However, the formula M₁V₁ has units mol·L⁻¹ × L = mol. Thus, in the formula, it is moles that are constant.