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The pH of the following acid solutions was measured using a pH meter - VCE - SSCE Chemistry - Question 5 - 2014 - Paper 1
Question 5
The pH of the following acid solutions was measured using a pH meter. Solution Volume Concentration nitrous acid 10.0 mL 0.10 M ethanolic acid 20.0 mL 0.10 M hypobr... show full transcript
Worked Solution & Example Answer:The pH of the following acid solutions was measured using a pH meter - VCE - SSCE Chemistry - Question 5 - 2014 - Paper 1
Step 1
Determine the relative strength of the acids
Answer
To calculate the pH, we first need to consider the relative strengths of the acids. Nitrous acid (HNO2) is a weak acid, while ethanoic acid (acetic acid, CH3COOH) is also a weak acid, but has a lower dissociation constant than nitrous acid. Hypobromous acid (HBrO) is a weak acid, and hypochlorous acid (HClO) is similarly weak. Generally, nitrous acid is considered stronger than ethanoic acid, given comparable concentrations.
Step 2
Evaluate acid dissociation constants
Answer
The acid dissociation constant (Ka) can provide insights into the strength of these acids. For example:
- HNO2 has a higher Ka, meaning stronger potential for hydrogen ion release.
- CH3COOH has a lower Ka, resulting in fewer hydrogen ions in solution. Thus, nitrous acid will yield a lower pH than ethanoic acid.
Step 3
Calculate pH for each solution
Answer
The pH of a strong acid can be approximated with the formula: For weak acids, we can use the formula: ext{pH} = - ext{log}(C) + rac{1}{2} ext{log} rac{K_a}{ ext{M}} where C is concentration, K_a is the acid dissociation constant, and M is the concentration at equilibrium. However, since all solutions are 0.10 M and considering their strengths, nitrous acid would still dominate in terms of lower pH.
Step 4