The following weak acids are used in the food industry - VCE - SSCE Chemistry - Question 3 - 2012 - Paper 1
Question 3
The following weak acids are used in the food industry.
Acid Common use Formula Structure Kₐ values
sorbic preservative C₆H₈O₂ 1.73 × 10⁻⁵
malic low-calorie fruit ... show full transcript
Worked Solution & Example Answer:The following weak acids are used in the food industry - VCE - SSCE Chemistry - Question 3 - 2012 - Paper 1
Step 1
What does the term ‘weak acid’ mean?
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Answer
A weak acid is one that does not completely ionize in water. This means that in a solution, a weak acid only partially dissociates into its ions, resulting in a lower concentration of free hydrogen ions ( ext{H}^+) compared to a strong acid at the same concentration. Therefore, weak acids typically exhibit higher pH values in solution.
Step 2
Why are two Kₐ values listed for malic acid?
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Answer
Malic acid is a diprotic acid, meaning it can donate two protons (H⁺). As a result, there are two distinct dissociation steps, each with its own Kₐ value. The first Kₐ corresponds to the dissociation of the first proton, while the second Kₐ relates to the dissociation of the second proton, reflecting the two-stage ionization process.
Step 3
Write an appropriate chemical equation that relates to the second Kₐ of malic acid.
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Answer
The equation that relates to the second Kₐ value of malic acid can be represented as:
