Question

Which of the following is the correct formula to calculate percent by mass? [Mass of solution (g) + mass of solute (g)] × 100 [Mass of solute (g) − mass of solution (g)] × 100 [Mass of solute (g) ÷ mass of solution (g)] × 100 [Mass of solution (g) ÷ mass of solute (g)] × 100

Answer 1

Answer:

Percent by mass is calculated by tihis formula, Mass of solute (g) ÷ mass of solution (g)] × 100.

Explanation:

For example: if you have a solution 45% m/m (mass percentege), you have 45 g of solute in 100 g of solution.

Answer 2

Answer:

C.  [Mass of solute (g) ÷ mass of solution (g)] × 100

Explanation:

For example  

If a solution of NaCl has a concentration of 1.50 M. The density of the solution is 1.06 g/mL. Then the concentration of solution by percent in mass?

Solution :  

Molarity is moles of solute present in 1L of its solution .

Hence the formula is

Molarity = (moles of solute) / (Volume of solution in L)  (unit is mol/L or M)

$= \frac {1.50mol}{1L}$

Let us convert the numerator and the denominator into mass in g

Numerator :                                  

mass = moles × molar mass

$=1.50mol \times 58.5 g/mol = 87.75g (solute)$

Denominator :                          

mass = density × volume

$=1.06g/1ml \times 1L = 1.06g/1ml \times 1000ml = 1060g$

The formula to find mass percentage is

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

% mass of NaCl =(mass of solute) / (mass of solution) × 100%

$= \frac {87.75g}{1060g} \times 100%\\=8.28%$

= 8.28% (Answer)