a. a 14 cm^3 sample of lake water is found to have 176.1 ng As. What is concentr
ID: 881946 • Letter: A
Question
a. a 14 cm^3 sample of lake water is found to have 176.1 ng As. What is concentration of arsenic in the sample in parts per billion assuming that the density of the lake water is 1.00g/cm^3
b.One of the volunteers suggests hiring an on site treatment company to remove the arsenic from the lake. The company claims that their process takes 2.08 days to remove 54.50 kg of As from the water source. 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 0.850 km^3.
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.
Explanation / Answer
a) solution weight = density x volume = 1 x 14 = 14 g
solute weight = 176.1 x 10^-9 g
concentration = (solute weight / solution weight ) x 10^9
= (176.1 x 10^-9 / 14 ) x 10^9
= 12.58 parts per billion
b)
1 km = 10^5 cm
0.850 Km3 = (0.850 x 10^5 cm)^3 = 85000 cm3
from problem (a)
14cm^3 volume of water contain -----------------> 176.1 ng of As
85000 cm3 volume of water contain --------------> ?
As weight = 176 .1 x 85000 / 14
= 1.069 x 10^6 ng
= 1.069 x 10^6 x 10^-9 g
=1.069 x 10^-3 g
= 1.069 x 10^-3 x 10^-3 kg
= 1.069 x 10^-6 kg
total mass of As = 1.069 x 10^-6 kg
(c)
2.08 days to remove ------------------> 54.50 kg of As from water
howmany days -----------------> 1.069 x 10^-6 kg As from water
days = 1.069 x 10^-6 x 2.08 / 54.50
= 4.079 x 10^-8 days
years = 4.079 x 10^-8 / 365
= 1.12 x 10^-10 years
1.12 x 10^-10 years will it take to remove all of the arsenic from the lake
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