Question

Calculate the amount of water (in grams) that must be added to (a) 6.80 g of urea [(NH2)2CO] in the preparation of a 9.95 percent by mass solution: g (b) 29.3 g of MgBr2 in the preparation of a 1.70 percent mass solution: g

Answer 1

Step-by-step explanation:

Amount of water required in each case:

(a)The mass% of the solution is:9.95

Mass of solute that is urea is 6.80 g

To determine the mass of solvent water use the formula:

`mass percent=(mass of solute)/(mass of solution) x 100\\\\9.95=(6.80g/mass of solution )x100\\mass of solution =(6.80 /9.95)x100\\=68.3 g`

Hence the mass of solvent = mass of solution - the mass of solute

=68.3 g - 6.80g

=61.5 g

Hence, the answer is mass of solvent water required is 61.5 g.

(b) Given mass%=1.70

mass of solute MgBr2 = 29.3 g

The mass of solvent water required can be calculated as shown below:

`mass percent=(mass of solute)/(mass of solution) x 100\\\\1.70=(29.3g/mass of solution )x100\\mass of solution =(29.3 g /1.70)x100\\=1720 g`

The mass of the solution is 1720 g.

Mass of solvent water = mass of solution - mass of solute

=1720 g - 29.3 g

=1690.7 g

Answer: The mass of water required is 1690.7 g.