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I am working on setting up an ICE table for adding 0.020 mol HCl to 1.0 L of 0.10 M propanoic acid. Since these are both acids (propanoic acid being the weaker one and HCl being strong), how would I set this up in an ICE table to calculate the pH of the resulting acid?

Edit: I was able to find an answer by taking the negative log of 0.02 to get the pH (because HCl is a strong acid). However, I am unaware with how to even set up the ICE table.

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    $\begingroup$ You should provide at least your failed trial, otherwise the question may be voted to be closed for not sufficient effort. $\endgroup$
    – Poutnik
    Nov 14, 2020 at 0:41
  • $\begingroup$ Thank you for your suggestion - I am unaware of how to set up the problem and was simply taking the negative log of 0.02 HCl due to the fact that it is a strong acid. $\endgroup$ Nov 14, 2020 at 1:43
  • $\begingroup$ Hint: There is the universal procedure to count with mass and charge balances and chemical equilibrium given by dissociation constants of weak acid and water. Then there is analysis what can be eventually neglected to simplify calculation. $\endgroup$
    – Poutnik
    Nov 14, 2020 at 6:05
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    $\begingroup$ What is the meaning of ICE ? $\endgroup$
    – Maurice
    Nov 14, 2020 at 10:17
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    $\begingroup$ @Maurice RICE chart or RICE box or ICE table. "tabular system of keeping track of changing concentrations in an equilibrium reaction. RICE stands for reaction, initial, change, equilibrium. ". Personally, I have never used them, or at least never heard the term until I came to CH SE site. The usage may be region or language specific. $\endgroup$
    – Poutnik
    Nov 14, 2020 at 12:18

1 Answer 1

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ICE tables tabulate amounts or concentrations pertaining to an equilibrium reaction: at the initial stage (I), how they change (C), and what they are at the end or at equilibrium (E). They are an alternative to solving multiple simultaneous equations (equilibrium constant expression, mass balance), instead using a single parameter (related to the extent of reaction $\xi$).

For the problem at hand, there is one reaction that goes to completion (strong acid) and one that attains equilibrium (weak acid, both protonated and deprotonated species present at equilibrium).

The ICE table needs to have species from the second reaction only. A good estimate of the hydrogen ion concentration is the concentration of hydrochloric acid (it dissociates completely, and we are ignoring the autodissociation of water for now).

$\begin{array}{|c|c|c|c|} \hline \ & [\ce{HP}] & [\ce{H+}] & [\ce{P-}]\\ \hline \text{I} & 0.1 & 0.02 & 0 \\ \text{C} & -x & +x & +x \\ \text{E} & 0.1-x & 0.02 +x & x\\ \hline \end{array}\\\\$

If you do the math, you will find that very little of the propanoic acid will dissociate, as the $\mathrm{p}K_\mathrm{a}$ is far from the initial pH.

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    $\begingroup$ [H+]=0.02, not 0.2 $\endgroup$
    – Poutnik
    Nov 14, 2020 at 13:59
  • $\begingroup$ @Poutnik I should stop answering questions when I am not wearing my reading glasses! $\endgroup$ Nov 14, 2020 at 14:39
  • $\begingroup$ I see, glasses are important part of my life too. $\endgroup$
    – Poutnik
    Nov 14, 2020 at 14:41

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