# How could the freezing point depression of #CaCl_2# be smaller than #NaCl#?

##### 1 Answer

#### Answer:

It depends on whether you are calculating on a molar or mass basis. Calcium chloride gives more freezing point depression per *mole* than sodium chloride, but less freezing point depression per *gram*.

#### Explanation:

Let's see how the mass basis is different. Say you have two solutions, one of them with 50 grams

For the *two* moles of ions, thus:

Now let's do this with the *three* moles of ions in solution. So:

The calcium chloride solution, with the same number of grams per liter, makes fewer ions in solution (**same mass concentration**.

However, you *can* get a lot more mass concentration into solution with **maximum possible** freezing point depression is greater with