Question

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 15.7 cm3 sample of lake water is found to have 164.5 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/cm3?

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 2.74 days to remove 41.90 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 0.710 km3?

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?

Answer 1

a) volume of sample of lake = 15.7 cm3 and it density =1 g/cc mass of water= volume* density = 15.7 gm

164. ng of As= 165.9*10^-9 gms of As

there is 165.9*10-9gm As/ 15.7 gms of water= 10.6*10^-9 gms of As/ gm of water

1ppb= 10-9

10.6*10-9 gm of As/ gm of water= 10.6 ppb

b) 0.71 km3 correspond to 7.1*1014 cm3

15.7 cm3 contains 164.5*10-9 gm of As

7.1*10¹⁴ cm3 containd 7.1*10¹⁴*164.5*10-9/15.7=7439172gms = 7439.172 kgs of As

c) 41.9 kgs are removed in 2.74days

7439.172 kgs are removed in 2.74*7439.172/41.9=486 days = 1.33 years