Do the acids follow the same pH trend as their starting concentrations are chang
ID: 495348 • Letter: D
Question
Do the acids follow the same pH trend as their starting concentrations are changed? For example, if they followed the same trend we would expect the two sets of data points to lie parallel to one another. Is this is what is observed? Why do they or don’t they follow the same trend?
Background:
We plotted pH vs. -log[HA] on a graph using data from nitric acid and acetic acid. After plotting, the pH trends seem to be parallel to each other. We know that Nitric acid is a strong acid and acetic acid is a weak acid.
Explanation / Answer
We know that nitric acid is a strong acid and acetic acid is weak acid
Nitric acid will dissociate completely to proton and nitrate ion
Now if we will increase the concentration of acid it will decrease the pH
pH = -log[H+]
[H+] depends upon the strength of acid
In case of weak acid (acetic acid) it will not dissoicate completely [it will have some particular degree of dissociation which is independant of concentration of acid]
Let the degree of dissociation of acetic acid = x %
The number of protons furnished by acetic acid will increase with increase in the concentration of acid however the percentage of protons will be the same with respect to the strength of acid
Hence the plot will give a parallel line for each of the acids
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