Sapling Learning Map Suppose a group of volunteers is planning on building a par

Question

Sapling Learning Map Suppose a group of volunteers is planning on building a park near a local lake. The lake is known to contain low levels of arsenic (As). Therefore, prior to starting construction, the group decides to measure the current level of arsenic in the lake. a) If a 12.5 cm3 sample of lake water is found to have 177.5 ng As, what is the concentration of arsenic in the sample in parts per billion (ppb), assuming that the density of the lake water is 1.00 g/cm? Number ppb One of the volunteers suggests hiring an on-site water treatment company to remove the arsenic from the lake. The company claims their process takes 2.67 days to remove 39.60 kg of As from a water source. b) Calculate the total mass (in kg) of arsenic in the lake that the company will have to remove if the total volume of water in the lake is 0.810 km3 Number kg c) Based on the company's claim and the concentration of arsenic in the lake, how many years will it take to remove all of the arsenic from the lake, assuming that there are always 365 days in a year? Number years Hint Previous Q Check Answer Next Exit

Explanation / Answer

Part a

Mass of sample water = volume x density

= 12.5 cm3 x 1 g/cm3

= 12.5 g

Mass of As in water = 177.5 ng x 10^-9g/ng

= 177.5*10^-9 g

Concentration of As in ppb = 177.5*10^-9 g / 12.5 g

= 1.42 x 10^-8

= 14.2 x 10^-9

= 14.2 ppb

Part b

12.5 cm3 contains = 177.5*10^-9 g As

0.810 km3 contains

= 177.5*10^-9 g x 0.810 km3 x 10^15 cm3 / 12.5 cm3 x 1km3

= 11502000 g x 1kg/1000g

= 11502 kg

Part C

Years to remove As

= (11502 kg) / (39.60 kg/2.67days)

= 775.513 days x 1year/365days

= 2.124 years

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