Citric and Aceitc Acid (1 Viewer)

[wrxsti]

Um Does anyone know which has a higher PH?

 

[Lucid Scintilla]

acetic (ethanoic) acid - CH3COOH - 4.75
citric acid - C6H8O7 - 3.13

Acetic acid has a higher pH.

Haven't you already done your HSC, though?

 

[Forbidden.]

acetic (ethanoic) acid - CH3COOH - 4.75
citric acid - C6H8O7 - 3.13

Acetic acid has a higher pH.

Haven't you already done your HSC, though?

They're both weak acids, but how do I know which one is weaker ?

 

[ssglain]

Ethanoic acid is monoprotic and citric acid is triprotic. If we're to assume complete ionisation in (say) 0.1M solutions of each acid, the hydronium concentration is 0.1M in ethanoic acid and 0.3M in citric acid. So the theoretical pH is -log(0.1)=1 for enthanoic acid and -log(0.3)=0.52 for citric. Theoretically, citric acid is stronger than ethanoic acid. It, too, is stronger in reality (as Lucid Scintilla showed us), but both ethanoic and citric acids have much higher pH values because neither ionises completely.

 

[Forbidden.]

Hmm monoprotic ...

CH₃COOH <--> CH₃COO^- + H⁺

Now about the triprotic nature of citric acid, the most frustrating thing about weak acids is writing the ionic equation for them.
According to you the [H⁺] concentration is 0.3M so I guess the best equation for that is:

C₆H₈O₇ <--> C₆H₅O₇^3- + 3H⁺

If not correct (the charge is incorrect or more than two products are formed) then I don't know , but my Chem teacher wouldn't put something this nasty in our exam.

 

[ssglain]

Hmm monoprotic ...

CH₃COOH <--> CH₃COO^- + H⁺

Now about the triprotic nature of citric acid, the most frustrating thing about weak acids is writing the ionic equation for them.
According to you the [H⁺] concentration is 0.3M so I guess the best equation for that is:

C₆H₈O₇ <--> C₆H₅O₇^3- + 3H⁺

If not correct (the charge is incorrect or more than two products are formed) then I don't know , but my Chem teacher wouldn't put something this nasty in our exam.

Yeah I would just be putting the overall equation (even though it hardly ever happens in reality) instead of a separate equation for each of the 3 steps for complete ionisation of citric acid.

 

[Eddyah]

The Fuck?

I thought citric would be stronger since it ionises better in water. 8.6% i believe while acetic is only 1.3%.

I may have this mixed up though.

 

[airie]

The Fuck?

I thought citric would be stronger since it ionises better in water. 8.6% i believe while acetic is only 1.3%.

I may have this mixed up though.

Citric acid is stronger than acetic acid. That's why it has a lower pH (ie. more acidic) than acetic acid at same concentrations. What's the problem?