Problem: In the atmosphere, sulfur dioxide and nitrogen dioxide react with water to give sulfurous acid and nitric acid. This produces “acid rain” which has a pH below 7 and can dissolve limestone. Sulfur dioxide, SO2, acts as a diprotic acid in aqueous solution. At 25°C the acidity constants are:SO2 (aq) + 2H 2O (l) ⇋ HSO3– (aq) + H3O+ (aq)               K a1 = 1.54 x 10–2HSO3– (aq) + H2O (l) ⇋ SO32– (aq) + H3O+ (aq)              K a2 = 1.02 x 10–7Calculate the pH of the above solution.A. 8.4B. 13.2C. 1.32D. 1.81E. 0.84

FREE Expert Solution

We are being asked to calculate the pH of the solution if the concentration of sulfur dioxide in water saturated with sulfur dioxide is 1.5 M


We're going to calculate the pH of the solution using the following steps: 

Step 1: Construct an ICE chart for the equilibrium reaction.
Step 2: Write the Ka expression.
Step 3: Calculate for the equilibrium concentration.
Step 4: Calculate pH.


Step 1: Construct an ICE chart for the equilibrium reaction.

Since we’re dealing with a weak acid and Ka is an equilibrium expression, we will have to create an ICE chart to determine the equilibrium concentration of each species:

SO2weak acidproton donor
H2O → will act as the weak baseproton acceptor


We will use the first equilibrium reaction given:

       SO2 (aq) + 2H2O (l) ⇋ HSO3 (aq) + H3O(aq)               Ka1 = 1.54 x 10–2

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Problem Details

In the atmosphere, sulfur dioxide and nitrogen dioxide react with water to give sulfurous acid and nitric acid. This produces “acid rain” which has a pH below 7 and can dissolve limestone. 

Sulfur dioxide, SO2, acts as a diprotic acid in aqueous solution. At 25°C the acidity constants are:

SO2 (aq) + 2H 2O (l) ⇋ HSO3 (aq) + H3O(aq)               K a1 = 1.54 x 10–2
HSO3– (aq) + H2O (l) ⇋ SO32– (aq) + H3O(aq)              K a2 = 1.02 x 10–7

Calculate the pH of the above solution.

A. 8.4

B. 13.2

C. 1.32

D. 1.81

E. 0.84

Frequently Asked Questions

What scientific concept do you need to know in order to solve this problem?

Our tutors have indicated that to solve this problem you will need to apply the Diprotic Acid concept. You can view video lessons to learn Diprotic Acid. Or if you need more Diprotic Acid practice, you can also practice Diprotic Acid practice problems.