The solubility of compound A in ethanol is .8g per 100ml at 0degreesC and 5.0g per 100ml at 78degreesC. What is the minimum amount of ethanol needed to recrystallize a 12.0g sample of compound A? How much would be lost in the recrystallization, that is, would remain in the cold solvent?

100 mL x 12g/5g = 240 mL = minimum amount ethanol to dissolve 12 g A.

0.8 g x 240/100 = 1.9 g is the solubility at 0o C in 240 mL so 1.9 g is what is lost. You would recover 12-1.9 = ??

To determine the minimum amount of ethanol needed to recrystallize a 12.0g sample of compound A, we can use the solubility values given at 0 degrees Celsius and 78 degrees Celsius.

First, we need to find out the maximum amount of compound A that can dissolve in ethanol at each temperature.

At 0 degrees Celsius:
Solubility = 0.8g/100ml
So, in 100 ml of ethanol, we can dissolve a maximum of 0.8g of compound A.

At 78 degrees Celsius:
Solubility = 5.0g/100ml
So, in 100 ml of ethanol, we can dissolve a maximum of 5.0g of compound A.

Now, we need to determine the amount of ethanol required to dissolve 12.0g of compound A at each temperature.

At 0 degrees Celsius:
We can set up the following proportion:
0.8g/100ml = 12.0g/x ml
Solving for x:
x = (12.0g * 100ml) / 0.8g
x = 1500 ml

At 78 degrees Celsius:
Similarly, we set up the proportion:
5.0g/100ml = 12.0g/x ml
Solving for x:
x = (12.0g * 100ml) / 5.0g
x = 240 ml

Therefore, to recrystallize a 12.0g sample of compound A, you would need a minimum of 1500 ml of ethanol at 0 degrees Celsius, and 240 ml of ethanol at 78 degrees Celsius.

Now, let's calculate the amount of compound A that would remain in the cold solvent.

At 0 degrees Celsius:
Since we needed 1500 ml of ethanol to dissolve 12.0g of compound A, and the solubility is 0.8g/100ml, then the total amount that could be dissolved in 1500 ml of ethanol is:
(0.8g/100ml) * 1500 ml = 12.0g

Therefore, at 0 degrees Celsius, no compound A would remain in the cold solvent.

At 78 degrees Celsius:
Since we needed 240 ml of ethanol to dissolve 12.0g of compound A, and the solubility is 5.0g/100ml, then the total amount that could be dissolved in 240 ml of ethanol is:
(5.0g/100ml) * 240 ml = 12.0g

Therefore, at 78 degrees Celsius, no compound A would remain in the cold solvent either.

In both cases, no compound A would be lost in the recrystallization process as all of it would dissolve in the ethanol solvent.