Question

why is MgCl2 more soluble in water than AlCl3

Answer 1

Hey there......

Because MgC12 is more polar than AlCl3

Hope it helped.......

Answer 2

Answer: Because $MgCl_2$ is more ionic as compared to $AlCl_3$

Explanation:

According to Fajans' Rule,  compounds are more likely to be ionic if there is a small positive charge on the cation, the cation is large, and the anion is small.

As we know on moving across the period, the atomic size keeps on decreasing due to increase in nuclear charge and addition of electrons in the same shell. Thus $Mg^{2+}$ is a larger ion as compared to $Al^{3+}$. Thus $MgCl_2$ is more ionic since $Mg^{2+}$ is a larger ion with a low charge.

As ionic compounds are more polar, thus they are more soluble in water.