Old mining operations often leach acidic water into nearby streams. This is call

Question

Old mining operations often leach acidic water into nearby streams. This is called acid mine drainage and it generally results from the oxidation of both metals and metal ores containing sulfur, so sulfuric acid is often the main culprit. This can be a real problem because it does not take much concentrated acid to change the pH of a large body of water. Also, many toxic metals are more soluble in acidic solutions, hence toxic metals are leached from the mine as well. Suppose that there is an old mine that is leaching water with a pH of 1.00 at the rate of 13.0 L per minute into a large stream that has a flow rate of 540000 L/min. What is the pH of the stream once the acid mine drainage has been mixed in? Assume the stream had a starting pH of 7.00 and it had no buffers. The units for the answer is pH units with an error interval of +/- 0.1 pH units

Explanation / Answer

Suppose that there is an old mine that is leaching water with a pH of 1.00 at the rate of 13.0 L per minute into a large stream that has a flow rate of 540000 L/min. What is the pH of the stream once the acid mine drainage has been mixed in? Assume the stream had a starting pH of 7.00 and it had no buffers. The units for the answer is pH units with an error interval of +/- 0.1 pH units

Answer:

pH =1.0

Flow rate = 13 L / min The hydrogen ion concentration = 10^-1 M

So [H+] in 13L = 13 X 10^-1 Moles

stream flow = 54000 L /min pH = 7

So H+ = 10^-7 M

Moles of [H+] = 54000 X 10^-7 moles

Total H+ ion concentration = Toal moles / total volume = 540000 X 10^-7 + 13 X 10^-1 / 540000 + 13

We can ignore 13 with respect to 54000

So concentration = 0.054 + 1.3 / 540000

Concentration = 1.354 / 540000 = 2.5 X 10^-6 Molar

so pH = -log[2.507 X 10^-6] = 5.6

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