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Which 0.1 M solution of the following acids has the highest pH? A - VCE - SSCE Chemistry - Question 20 - 2011 - Paper 1
Question 20
Which 0.1 M solution of the following acids has the highest pH? A. nitrous acid B. ethanoic acid C. methanoic acid D. hypobromous acid
Worked Solution & Example Answer:Which 0.1 M solution of the following acids has the highest pH? A - VCE - SSCE Chemistry - Question 20 - 2011 - Paper 1
Step 1
Determine the strength of each acid
Answer
To assess which 0.1 M solution has the highest pH, we need to determine the strength of each acid listed. Stronger acids dissociate more completely in solution, resulting in lower pH values.
- Nitrous Acid (HNO2) is a weak acid with a pKa of approximately 3.37.
- Ethanoic Acid (CH3COOH) also is a weak acid, with a pKa of around 4.76.
- Methanoic Acid (HCOOH) is slightly stronger than ethanoic acid with a pKa of about 3.75.
- Hypobromous Acid (HBrO) is another weak acid with a pKa of approximately 8.70, making it very weak relative to the others.
Step 2
Compare the acids based on their pKa values
Answer
Comparing the pKa values allows us to rank the acids by strength:
- Strongest : Nitrous Acid (pKa 3.37)
- Next : Methanoic Acid (pKa 3.75)
- Then : Ethanoic Acid (pKa 4.76)
- Weakest : Hypobromous Acid (pKa 8.70)
Since hypobromous acid has the highest pKa, it is the weakest acid among the choices provided.
Step 3