Question

Calculate how much 95% ethyl alcohol will be required to dissolve 0.75 g of sulfanilamide at 78°c

Answer 1

95% ethyl alcohol  
Mass of sulfanilamide = 0.75 g = 750 mg 
Temperature = 78 c 
Solubility of sulfanilamide in 95% ethyl alcohol at 78°C is 210 mg/mL.  
(210 mg) / (1 mL) = (300 mg) / (x mL) => x = 300 / 210 => x 1.43 mL.

Answer 2

Missing question: sulfanilamide has a solubility in 95% ethanol of 210 mg/ml at 78 degree Celsius.
m(sulfanilamide) = 0,75 g = 0,75 · 1000 = 750 mg.
210 mg : 1 ml = 750 mg : V(ethyl alcohol).
210 mg · V(ethyl alcohol) = 750 ml · mg.
V(ethyl alcohol) = 3,57 ml.
Answer is: 3,57 ml of 95% ethyl alcohol will be required.