# Volume/volume units question

1. Jan 10, 2017

### ReidMerrill

I'm looking through articles for a presentation in college and I ran across the units volume/volume. (V/V)
From what I understand v/v is calculated with the formula (vol. solute/total volume). One of the articles has figures with over 100 v/v. How is this possible? Shouldn't it be between 0 and 1 or 0% and 100%

2. Jan 10, 2017

### Staff: Mentor

Volume is not additive. If you mix 50 mL of water with 50 mL of ethanol you'll get 96.4 mL of solution.

3. Jan 10, 2017

Why does this happen? I can see how it would work if the two substances were at different temperatures initially but can't think of anything else that would cause it.

4. Jan 10, 2017

### Bystander

5. Jan 11, 2017

### Staff: Mentor

Imagine adding sand to marbles, with sand filling gaps between marbles. Is the final volume sum of volumes?

That's not the only way it happens, but it will give you an example.

6. Jan 12, 2017

### ReidMerrill

That's a good analogy. It was talking about gas adsorbing to charcoal. I didn't take into account the nooks and crannies in charcoal that give it 'internal volume' for lack of a better word

7. Jan 13, 2017

### mjc123

That adds another complication, because when a gas is adsorbed on charcoal it is not a gas in the adsorbed form. It is not surprising that 1 cm3 of charcoal may adsorb 100 cm3 of gas, but the volume occupied by the adsorbate molecules in the charcoal is much less than 100 cm3. Remember that the volume of a gas is mostly empty space. As a very rough guide, the volume of a gas at STP is of the order of 1000 x its volume as a liquid. So the volume occupied by the adsorbate may be more like ca. 0.1 cm3.