Posted by Sophie on .
The solubility of benzoic acid in water is 2.56g in 100cm3 at 79 C and 0.29g in 100cm3 at 20 C. What is the minimum volume of water in which 1g of benzoic acid can be dissolved at 79 C?
I set up a dimensional analysis but since the question gives 2 sets of results, I do not know what to do.

Chemistry 
DrBob222,
The dimensional approach will work. The question asks for the minimun solubility AT 79 DEGREES C; therefore, just ignore the solubility of benzoic acid at 20 degrees C. As far as this problem goes, you don't really care what the solubility is at 20.

Chemistry 
Sophie,
but what equation is used to find it? the delta H/RT equation won't solve for anything

Chemistry 
jo,
I think you solve the first two given values and find delta H and then used the delta H to find solubility of water

Chemistry 
kobe,
what equation do you use??

Chemistry 
GK,
The equation I would set up based on the information given is:
2.56g Benz. Acid /100cm^3 water = 1.00g Benz. Acid / x cm^3
Without the units,
2.56 /100 = 1.00 / x
Solve the above equation for "x" to get the minimum volume of water in cm^3 that would be needed to dissolve 1.00g of Benzoic acid.