Question

a mixture is made between 15.00 grams of sugar and 42.00 mL of water (dH2O= 1.00g/mL). What is the mass percent of the sugar in the solution? (report to 4 SF)

A student dissolved 7.5 grams of NaCl= 58.5g/mol) in enough water to make 62 mL of solution. What is the molarity of the solution? (report answer to 2 SF).

Answer 1

a)

Mass percent of sugar

=( mass of sugar / mass of solution) × 100%

Mass of sugar = 15.00 g

Mass of water = 42.00 mL × ( 1.00 g / mL ) = 42.00 g

Mass of solution = mass of water + mass of sugar

= 15.00 g + 42.00 g

= 57.00 g

% mass =( 15 g / 57 g)×100%

% mass = 26.32%

Molarity = moles of solute / Liters of solution

Moles of solute:

7.5 g NaCl × ( 1 mol NaCl / 58.5 g NaCl)

= 0.128 mol NaCl

Volume = 62 mL × ( 1 L / 1000 mL) = 0.062 L

Molarity = 0.128 mol / 0.062

= 2.1 M

Hence the molarity of solution is 2.1 M