# Homework Help: How to calculate displacement from density?

1. Aug 10, 2012

### volpe

If this the wrong section to post this, please know that I am very sorry, but I don't know much about any of the things going on, on here so please bare with me.

Say you got some powder, and say this powder has a density of 1.06g/cm3 (or 1.06g/mL, right?).

Now say you want to put 2500mg of this powder in a solvent mixture (made from cottonseed oil, 0.3mL benzyl alcohol and 1.7mL benzyl benzoate), that you want it to be total of 10ml, with the powder being at a concentration of 250mg/mL

How would one go about calculating the displacement caused by this powder, which will then determine how much oil one would need to use?

2. Aug 10, 2012

### volpe

Simple way of putting it:

Powder has a density of 1.06g/cm3

How much will 1000mg of the powder displace 10ml of water

3. Aug 10, 2012

### voko

If the powder is completely insoluble, and does not form any kind of compounds with water, then the resultant volume is a simple sum of the volume of the powder and of the liquid.

Otherwise, you will need the properties of the resultant solution/compound.

4. Aug 10, 2012

### volpe

Okay let us say the powder is insoluble, how would one go about calculating thing (I need a formula)

5. Aug 10, 2012

### voko

Say the concentration is c mg/mL.

Then in volume V ml of the mixture, you will have m = cV mg of the powder.

The density of the powder is ρ mg/mL, so mass m corresponds to volume v = m/ρ mL.

Then the volume of the filler liquid is u = V - v mL.

I am sure you can substitute and simplify the rest. But mind the units!