# Question #9afee

##### 1 Answer

Your solution's freezing point depression will be equal to

#### Explanation:

You know that the **mole fraction** of sodium hydroxide is equal to **1/5**. This means that the mole fraction of water will be

This means that, for *evey mole* of sodium hydroxide, your solution contains **4 times more** moles of water. Let

The number of moles of water will thus be

The equation for *freezing point depression* looks like this

**cryoscopic constant** - depends on the solvent;

**van't Hoff factor** - the number of ions per individual molecule of solute.

The molality of the solution is defined as the number of moles of solute, in your case sodium hydroxide, divided by the mass of the solvent, in your case water, expressed in **kilograms**!

You can determine the mass of water by using its molar mass

Since sodium hydroxide is a strong electrolyte, it will dissociate completely in aquesous solution to give sodium cations,

This means that **1 mole** of sodium hydroxide produces **1 mole** of **1 mole** of **2**.

Therefore, the freezing point depression will be

Rounded to two sig figs, despite the fact that you only gave one sig fig for the mole fraction of sodium hydroxide, the answer will be