Suppose a group of volunteers is planning on building a park near a local lake.
ID: 914574 • Letter: S
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. If a 10.1 cm^3 sample of lake water is found to have 159.1 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^3? 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 2.84 days to remove 41.20 kg of As from a 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 0.730 km^3. 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)
V = 10.1 cm^3
density = 1 g/cm^3
mass = density * V = 1 g/cm^3 * 10.1 cm^3 = 10.1 g
mass of As = 159.1 *10^-9 g
mass % in ppb = mass of AS *10^9/water
= 159.1*10^-9 * 10^9 / 10.1
=15.8
Answer: 15.8
b)
V= 0.730 km^3 = 0.730*(10^5)^3 cm^3= 7.3*10^14 cm^3
density = 1 g/cm^3
mass = density * V = 1 g/cm^3 * 7.3*10^14 cm^3 = 7.3*10^14 g
10.1 g water has 159.1 ng As
7.3*10^14 g of water will have = 159.1 *7.3*10^14 / 10.1 ng
= 1.15*10^16 ng
= 1.15*10^7 g
= 1.15*10^4 Kg
Answer: 1.15*10^4 Kg
c)
number of days = 1.15*10^4 * 2.84 / 41.2 = 793 days = 793/365 = 2.2 years
Answer: 2.2 years
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