Measures of Concentration: Molality and Other Calculations — Quiz
Question 18 • Chemistry
A teacher wants to prepare a 0 point 0 1 0 ppm solution of arsenic pentoxide in the laboratory for calibrating a water quality testing system. If the teacher uses 500 point 0 milliliters of water (which has a mass of 500 point 0 g ), what mass of arsenic pentoxide should the teacher mix to get the required solution? Use ppm is equal to mass of solute over mass of solution times 10 to the 6th power
Answer
A
5 point 0 times 10 to the negative 6 power g
B
5 point 0 times 10 to the negative 2 power g
C
2 point 0 times 10 to the negative 11 power g
D
2 point 0 times 10 to the negative 5 power g
Explanation
A concentration of 0.010 ppm means 0.010 g of arsenic pentoxide per 1,000,000 g of solution. For about 500.0 g of solution, the needed mass is (0.010 ÷ 1,000,000) × 500.0 = 5.0 × 10⁻⁶ g. The correct choice is 5.0 × 10⁻⁶ g.
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