Chemistry Practice Problems Diprotic Acid Practice Problems Solution: In the atmosphere, sulfur dioxide and nitrogen dio...

# Solution: 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 concentration of sulfite (SO32–) in the above solution.

###### 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 10–2
HSO3– (aq) + H2O (l) ⇋ SO32– (aq) + H3O(aq)              K a2 = 1.02 x 10–7

Calculate the concentration of sulfite (SO32–) in the above solution.

###### Solution

We are being asked to calculate the concentration of sulfite (SO32) in the solution if the concentration of sulfur dioxide in water saturated with sulfur dioxide is 1.5 M

We're going to calculate the concentration of sulfite (SO32–) in two parts:

1st Part: Calculate the concentration of hydrogen sulfite (HSO3) using the 1st equilibrium reaction:

Step 1: Construct an ICE chart for the 1st equilibrium reaction to calculate for the concentration of
Step 2: Write the Ka1 expression.
Step 3: Calculate for the equilibrium concentration.

2nd Part: Calculate the concentration of sulfite (SO3) using the 2nd equilibrium reaction:

Step 1: Construct an ICE chart for the 1st equilibrium reaction to calculate for the concentration of
Step 2: Write the Ka2 expression.
Step 3: Calculate for the equilibrium concentration.

1st Part: Calculate the concentration of hydrogen sulfite (HSO3) using the 1st equilibrium reaction:

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: View Complete Written Solution

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