Question

If the concentration of atmospheric CO₂ were double from its current value of 390 ppm, what would be the calculated pH of rainwater (assuming that CO₂ were the only acidic input)? With respect to rising CO₂ levels, do we have to be concerned about enhanced acidity of rain in addition to potential climate warming?

Answer 1

a)

pH = -log[H+]

then

CO2(g) + H2O(l) --> H2CO3(aq)

H2CO3(aq) --< H++ HCO3-(Aq)

Ka1 = [H+][HCO3-]/[H2CO3]

get

[CO2] = mol of CO2 / Volume

390 ppm = 390 mg of CO2 / liter of air

mol = mass/MW = 390/44 = 8.86363 mmol = 8.86363*10^-3 mol

P-CO2 = (8.86363*10^-3)*Ptotal = 8.86363*10^-3 atm

CO2 in water = H*P-CO2

CO2 in water = (3.4*10^-2) *8.86363*10^-3 = 0.0003013 M of CO2 in water

assume CO2 = H2CO3

[H2CO3] = 0.0003013 M initially

10^-6.34 = x*x/(0.0003013-x)

x = [H+] = 1.15*10^-5

pH= -log(x) = -log(1.15*10^-5) = 4.93

b)

yes, we need to be concerned

since many materials, such as CaCO3 or anyt other minerals will react to form

CaCO3 + H+ --< CaO + CO2(g)

then, this affects directly marine life overall