Home » Uncategorized » Will the solution be acidic/alkaline/neutral, when the CH3COO- ion alone is dissolved in water?

Will the solution be acidic/alkaline/neutral, when the CH3COO- ion alone is dissolved in water?

As you know, when ethanoic acid (CH3COOH) is dissolved in water, the solution formed will be acidic due to the presence of the dissociated H+ ions.  But what happens if you dissolve a CH3COO ion by itself into water. Will the solution be acidic/alkaline/or neutral?

Ans: Alkaline

Tell me why! (Ain’t nothing but…)

Again, we need to make some reference to your existing knowledge. As you know, ethanoic acid is a weak acid and dissociates partially in water to produce H+ ions and CH3COO ions.

The fact that it dissociates only partially implies that the CH3COOH is very unwilling to give up its H+ yes? Put another way, the CH3COO ion has relatively strong attraction to the H+ and is unwilling to give it up.

So, when you dissolve the CH3COO ion by itself into water it is attracted to the H atom of the water (Remember that water is a polar molecule with permanent partial positive charges on the H and partial negative charge on the O).

It is then able to hydrolyse (break apart) the water molecule, stealing the hydrogen for itself to form a CH3COOH molecule, leaving behind an OH- ion causing the solution to be alkaline!

CH3COO

In equation form:

CH3COO (aq)  +  H2O(l)  ⇌  CH3COOH(aq)  +  OH(aq)

Ah ha! I know what you guys are thinking… Since I form CH3COOH, the solution will be acidic no? Imagine this situation…

I dissolve 100 CH3COO- ions into water.

According to the equation above, I should get 100 CH3COOH molecules and 100 OH- ions. (Stage1)

As you know, CH3COOH is a weak acid, so it dissociates partially in water. So out of 100 CH3COOH molecules, maybe 3 will dissociate to give me 3 CH3COOand 3H+. (Stage2)

So, now, the solution contains 3 H+, 3 CH3COO, 97 CH3COOH molecules (from stage 2) and 100 OH ions (from stage 1). Since there are more OH ions than H+ ions, the solution is alkaline! Mind reading complete!

CH3COOd2

Based on feedback from T1, I realize that perhaps, the table form isn’t the best presentation.. Perhaps the diagram below would help you understand better?

CH3COOD3

Thank you Ms S (Sec3, 2013) for asking such an interesting question & T1 for her feedback!

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