# A 2% by weight aqueous solution of NaCl (MW= 58.45) has a boiling point of 100.31 °C. What is the van't Hoff factor for NaCl?

##### 1 Answer

The experimental value of the van't Hoff factor is 1.7.

The formula for boiling point elevation is

#color(blue)(|bar(ul(color(white)(a/a) ΔT_b = iK_bm color(white)(a/a)|)))" "#

This can be rearranged to give

We must now calculate the molality of the solution.

**Calculating the molality**

Assume that we have 100 g of the solution.

Then we have 2 g of NaCl and 98 g of water.

The formula for molality is

#color(blue)(|bar(ul(color(white)(a/a) "molality" = "moles of solute"/"kilograms of solvent"color(white)(a/a)|)))" "#

∴

Now we can calculate the

**Calculating the #i# factor**

The van't Hoff factor for NaCl is 1.7.