# You have 1 L of 100 proof (50% V/V) Scotch whisky (ethanol, #C_2H_5OH#). Calculate the molarity, the mole fraction, the molality of the ethanol and if the temperature drops to -10C could you still drink the whisky? Density of ethanol =0.79g/ml kf=-1.86C/m

##### 1 Answer

**!! LONG ANSWER !!**

The first thing you need to do is determine exactly how much ethanol your **1-L** sample contains.

Since you're dealing with a **50% v/v** solution, you'll get **50 mL** of ethanol for every **100 mL** of solution, which means that you have

Use the density of ethanol to determine how many grams you have in the 1-L sample

Use ethanol's molar mass to determine how many moles you have

Since molarity is defined as moles of solute divided by liters of solution, you'll get

To get the mole fraction of ethanol, you need to determine how many moles of water you have in the 1-L sample.

Since you have **500 mL** of ethanol in the 1-L bottle, you'll of course also have **500 mL** of water. Use water's density and its molar mass to determine how many moles you have

The total number of moles present in the solution will be

The **mole fraction** of ethanol will be

Molality is defined as moles of solute per kilogram of solvent, so you'll get

Now you have to determine whether or not you can still drink the whiskey if the temperature of the sample is dropped to

To do that, you have to determine if the amount of alcohol present in the sample would *lower the freezing point of water* enough to allow for the solution to remain liquid at that temperature.

The equation for freezing point depression is

**van't Hoff factor**, which takes into account the number of particles produced by a compound when dissolved in solution.

Since you're dealing with a non-electrolyte, the van't Hoff factor will be equal to **1**.

So, your solution will have a freezing point of

Therefore, you can still drink the whiskey at

**SIDE NOTE** *I've given all the answers with two sig figs, but I should have used 1 sig fig, since that is all you gave for the volume of the sample.*