Problem: Calculate the pH of a solution that is 1.15×10−3 M in HCl and 1.20×10−2 M in HClO2.

FREE Expert Solution

We’re being asked to calculate the pH of a solution that is 1.15×10−3 M in HCl and 1.20×10−2M in HClO2.

HClO2 is an oxyacid, and in order to be considered strong, there must be 2 or more oxygens than Hydrogens. 

HClO2 having only one more oxygen than hydrogen is not enough to make it a strong acid, therefore it a weak.

Remember that weak acids partially dissociate in water and that acids donate H+ to the base (water in this case): 

The dissociation of HClO2 is as follows.

HClO2(aq) + H2O(l)  H3O+(aq) + ClO2(aq) Ka = 1.1 × 10–2

HCl is a strong acid. It dissociates completely in aqueous solution with HClO2

                      HCl(aq)    →         H(aq)       +      Cl – (aq)

                After dissociation    (1.15 x 10-3)    (1.15 x 10-3)

That is why initially, we already have a [H3O+] concentration of 1.15 x 10-3 M. 

From this, we can construct an ICE table. Remember that liquids are ignored in the ICE table.

The Ka expression for HClO2 is:

Ka = productsreactants= [H3O+][ClO2-][HClO2]  Liquids are ignored in the Kexpression.

Note that each concentration is raised by the stoichiometric coefficient: [HClO2], [H3O+] and [ClO2] are raised to 1. We also have a common ion from the 1.15 x 10-3 M HCl which is [H3O+].

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Problem Details

Calculate the pH of a solution that is 1.15×10−3 M in HCl and 1.20×10−2 M in HClO2.

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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 Weak Acids concept. If you need more Weak Acids practice, you can also practice Weak Acids practice problems.

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