Answer:
a. 25.8 g of water
b. 1720.4 g of water
Explanation:
A percent by mass, means the grams of solute in 100 g. of solution. So, 16.2 g of urea are contained in 100 g of solution.
Then, solute mass + solvent mass = solution mass
16.2 g of urea + solvent mass = 100 g
solvent mass = 100 g - 16.2 g → 83.8 g
Now we can make the rule of three:
16.2 g of urea use 83.8 g of water
then, 5 g of urea would use (5 . 83.8) / 16.2 = 25.8 g of water
b. 1.5 % by mass, means 1.5 g of solute in 100 g of solution.
So water mass, for this solution will be 100 g - 1.5 g = 98.5 g
Now, we apply the rule of three:
1.5 g of solute use 98.5 of water
26.2 g of solute will use (26.2 . 98.5)/1.5 = 1720.4 g