A. The United States presently emit to the atmosphere 1.3x109 moles day-1 of NOX

ID: 298179 • Letter: A

Question

A. The United States presently emit to the atmosphere 1.3x109 moles day-1 of NOX and

1.0x109 moles day-1 of SO2. We assume that all of the emitted NOX and SO2 are

precipitated back over the United States as HNO3 and H2SO4, respectively (this is not

a bad approximation). The area of the United States is 1.0x107 km2 and the mean

precipitation rate is 2 mm day-1. Assuming that HNO3 and H2SO4 are the only

impurities in the rain, what is the resulting mean pH of precipitation over the United

States.

B. The actual range of rainwater pH values over the United States is 4.2-5.5. Explain

your estimate of rainwater acidity in question 1 relative to the actual range.

Answer: A

The reaction for the given condition are as follows;

NOx HNO3 H+ (1.3x109 moles)

SO2 H2SO4 2 H+ (1.0x109 moles)

And the volume of rain can be calculated as follows:

Volume= (1.0x107 km2 )*(1x103 m/1 km)2*(2x10-3 m) = 2x1010 m3 = 2x1013 liters

And the formula of Molarity are as follows;

Molarity= No. of moles / in litre

Therefore, the molarity of hydrogen ion [H+ ] in volume of rain = (3.3x10 moles)/(2.0x1013 liters) = 1.7x10-4

Hence, the pH value can be calculated as follows;

pH = -log([H+ ]) = 3.8

Answer:B

The value of pH is different from the actual range of rainwater because in part A we did not included the bases such as NH3 and CaCO3.

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