To solve this problem we need to keep in mind the <em>definition of molarity</em>:
Molarity = moles / volume
First we<u> calculate the moles of AlCl₃ </u>in 0.672 L of a 4.78 M solution:
Moles = Molarity * volume
Moles = 4.78 M * 0.672 L
Moles = 3.212 moles
Then we <u>calculate the new molarity of the AlCl₃ solution</u> using that <em>number of moles, which remains the same throughout the evaporation process</em>: