Problem: Calculate the pH and equilibrium concentration of all species present in a 0.150 M carbonic acid solution. For carbonic acid (H2CO3: Ka1 = 4.3 x 10-7 and Ka2 = 4.8 x 10-11 ).

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We are being asked to calculate the pH of the solution and equilibrium concentration of each species if the concentration of H2COis 0.15 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:

H2COweak acidproton donor
H2O → will act as the weak baseproton acceptor


We will use the first equilibrium reaction given:

       H2CO3  +  H2O (l) ⇋ HCO (aq) + H3O(aq)               Ka1 = 4.3 x 10–7

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Problem Details

Calculate the pH and equilibrium concentration of all species present in a 0.150 M carbonic acid solution. For carbonic acid (H2CO3: Ka1 = 4.3 x 10-7 and Ka2 = 4.8 x 10-11 ).

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