3. Calculate the pH of natural rainwater at 25°C, given that the CO2 concentrati

Question

3. Calculate the pH of natural rainwater at 25°C, given that the CO2 concentration in air is 372 ppm (present level), and that for carbon dioxide the Henry's Law constant K, -3.4x102 Assume that the following reaction is the only significant source of acidity: H2CO HCO H 4. Balance the following equations: iii. SO42-+ Fe2O3 + C + H2O = FeS2+ HCOS + CO32- 5. A power plant burns 10,000 metric tons of coal (assume it is pure C) per day and emits stack gas with 100 ppmv NO. If it uses 10% excess air (which is 21 mol% ), what is the daily output of NO?

Explanation / Answer

3) Given:

CO2 concentration in air = 372 ppm

KH = 3.4 x 10-2mol/l/atm

Ka = 4.5 x 10^-7mol-L

Step1 Calculate [CO2 (aq)]

[CO2 (aq)] in rain drops remains constant at KH. PCO2

So, at 372 ppm of CO2 and total atmospheric pressure of 1 atm,

PCO2 = 372/10^6 = 3.72 x 10^-4 atm.

[CO2 (aq)] = 3.4 x 10^-2mol/l/atm x 3.72 x 10^-4 atm. = 1.26 x 10^-5M

Step2 Calculate [H+]

Reaction: CO2 + H2O H+ + HCO3-

Ka = 4.5 x 10^-7

So, [H+] = [HCO3-] (assuming no other sources of H+)

Ka = [H+][HCO3-]/[CO2]

Or

Ka = [H+][H+]/[CO2]

[H+]2 = 4.5 x 10^-7 x [CO2]

[H+]2= 4.5 x 10^-7 x 1.26 x 10^-5M

[H+]2= 5.67 x 10^-12

[H+] = 2.38 x 10^-6M

Step2 Calculate pH

PH = -log [H+]

= -log [2.28 x 10^-6]

PH = 5.64

Related Questions

Navigate

• Browse (All)
• Browse 3
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.