# College Chemistry

posted by Anonymous

a mixture contains two crystalline solid X and Y. Decide if pure X can be obtained by a proper recrystallization using solvent A. Include the exact volumes of solvent used and the amount of pure X obtained.

GIVEN:
Solubility of X in boiling A :200mg/ml
solubility of X at room temp.: 20mg/ml
solubility of Y at boiling A : 200mg/ml
solubility of Y at room temp.: 20mg/ml
amount of X in mixture: 400mg
amount of Y in mixture: 30mg

1. DrBob222

Suppose you take 2 mL of boiling A.
X = 2 mL x 200 mg/mL = 400 mg so all of X will dissolve.

Y = 2 mL x 200 mg/mL = 400 mg so all of Y will dissolve.

Now cool the solution to room temperature. How much X and Y will recrystallize?
2 mL x 20 mg/mL = 40 mg X will stay in solution; 400 - 40 = 360 mg X will crystallize.

For Y,
2 mL x 20 mg/mL = 40 mg Y will stay in solution; you had only 30 so none will crystallize.

2. Anonymous

I'm guessing that 2mL of boiling A came from (400mg)(1mL/200mg)= 2mL

So we don't have worry about the Y at boiling A? which will be 0.15mL if we do the calculation.

3. DrBob222

You add enough boiling A to dissolve all of X (of course it will dissolver all of Y, too). Using 0.15 mL of boiling A will dissolve all of Y and some of X. In fact I suppose you could get pure X this way, too, although it isn't the usual way we think of recrystallization.
200 mg/mL x 0.15 mL = 30 mg X will dissolve leaving 400-30 = 370 mg X behind, BUT
1. 0.15 mL is a small volume to be working with, and you would have trouble controlling the volume and losing volume as it sticks to the walls of the vessel,
2. I would want to add just a little more than 0.15 because this JUST barely gets all of Y in solution.
3. I doubt this is the way your prof expects you to answer.

4. Anonymous

I was also thinking so we can't add the two volume of A together? So like for X in boiling A there is 2mL and in Y there is 0.15ml. So all together solvent A would be 2.15mL.

all of Y would still be gone but for X instead of 360mg i would get 357mg

5. DrBob222

In general, we assume that we need only one volume. In this case, however, an extra 0.15 mL couldn't hurt anything. As you point, however, it affects the yield.

## Similar Questions

1. ### ORG CHEM LAB

Im doing a conclusion on a lab of acetaminophen. We were to take a melting point of the crude smale of acetaminophen and melting point of the crystallized acetaminophen. The mp for crude sample: 169.2 degree C The mp for crystallized …
2. ### chemistry ap

Why would [23.8-(.0588)(23.8)] be the proper setup to determine the vapor pressure of a solution at 25 Celsius that has 45g of C6H12O6, glucose (MM=180gxmol^-1), dissolved in 72g of H2O?
3. ### Chemistry

A student determined that ethanol was the best solvent to use for a recrystallization based on small scale trials. When the recrystallization was carried out on a larger scale, no crystals were obtained on cooling the hot solution. …
4. ### Organic Chemistry

In order to obtain pure synthetic plant hormone, a 2:1 mixture of water and ethanol is used as the crystallizing solvent. Why is a solvent mixture used?
5. ### organic chemistry

which of the 3 solvent would not be suitable recrystallization solvent for acetanilide?
6. ### chemistry

Assume the density of aqueous HCl is the same as water (1.0 g/mL) and use the densities of ethanol (0.789 g/mL) and water as well as the actual amount of recrystallization solvent used to calculate the mass of recrystallization solvent.
7. ### Chemistry

Which of the following results from the presence of a solute in a given solvent?
8. ### Orgo Lab

Recrystallization is often used at the end of a synthesis. Choose the most accurate answer/s to explain the purpose of recrystallization and how it is done effectively?
9. ### chemistry

1. You are given a mixture containing two compounds, A and B. Both compounds have a solubility of 1 g/ 100 mL of solvent at 20 °C and 16 g/ 100 mL of solvent at 100 °C. The sample is composed of 3.5 g of A and 10 g of B. At 100 °C …
10. ### Chem

Which of the following results from the presence of a solute in a given solvent?

More Similar Questions