Question

Noke Lew weighs out 50.0 g of sodium chloride (NaCl) salt. She adds 300.0 g of water, so her total solution mass equals the salt plus the water together. Calculate the percent by mass of NaCl in her solution. Answer to 3 significant figures with appropriate units.

Doc Inmaking creates another solution by weighing 18.34 mg (0.01834 g) of Vitamin C with an analytical balance. He dissolves it in water to a total volume of 250.0 mL using a volumetric flask. He knows he has a dilute aqueous solution, so when he calculates the parts per million of Vitamin C he can use the shortcut. Calculate the parts per million of Vitamin C in Doc’s solution. Answer to 4 significant figures with appropriate units.

Answer 1

Mass of NaCl = 50 gm

Mass of solution = Mass of water + Mass of NaCl added

=> 300 + 50

=> 350 gm of solution

Percent by mass of NaCl = (Mass of NaCl/Mass of solution) * 100

=> 50/350 * 100

=> 100/7 = 14.2857

Answer in three significant figures = 14.3%

2)

ppm = 1 mg solute per Liter of solution

Amount of Solute = 18.34 mg

Volume of solution = 250 mL = 0.25 L

Hence ppm of Vitamin C = 18.34/0.25 ppm = 73.36 ppm

Hence the answer to four significant figures is 73.36 ppm or mg/L