GEN CHEM: How many grams of sugar are needed to prepare a 14 % by mass solution in 0.060 L of ethanol (d = 0.789 g/mL)? answer is 7.7g... how do i do this?

Question

GEN CHEM: How many grams of sugar are needed to prepare a 14 % by mass solution in 0.060 L of ethanol (d = 0.789 g/mL)?   answer is 7.7g... how do i do this?

aaronq · Answer

"14 % by mass" means that in 100g of solution 14 g are just solute (in this case sugar) and 86 g are solvent (in this case ethanol).

so you have 60 mL of ethanol. Using the density you find that it weighs:

$\rho=\dfrac{m}{V} \rightarrow m=V*\rho=60mL*0.789 g/mL =47.34 g$

so 47.34 g are 86% of the mass you need, can you find the mass of the solute (sugar) now?