hydrochloric acid vs. citric acid pH HELP QUICK

[HeroinSIK]

Hello all I need some help quick from you regarding an extraction.

If the lab calls for 3 grams of citric acid per liter of water, about how much would that be equal to if using hydrochloric acid (29%) in liquid form?

If I had a thick, liquid, soup of plant matter, would this affect the way the pH test strips read because of the thickness?

Or would I just have to keep adding a pH reducer to get a fairly acidic solution around of around 3 or 4.

 

[HeroinSIK]

by the way that smile face was supposed to be a percent sign. The acid is 29 percent.

 

[BilZ0r]

I don't know how to do pKa /pH calculations on compounds with multiple pKa's
pKa1 3.15
pKa2 4.77
pKa3 5.19
For anyone who does.

Meanwhile, Ive always found that you can use pH test strips to read pHs in thick liquids, it's more colored ones that are problematic.

Still if you're doing a classic acid base extraction, pH 3 is where I would aim.

 

[Smyth]

If the lab calls for citric acid then you'd be better to use it IMO. Citric acid is sold in the grocery store and is quite different physico-chemically to HCl.

 

[fastandbulbous]

I'm not prepareed to look through a physical chemistry book to work out dissociation constants for all three carboxylic acid groups of citric acid, but if you feel the urge to do such, be my guest; that said, I'd have to just reiterate what others have said, use citric acid if it states to use citric acid. It's not expensive or difficult to obtain, so why piss aroundf with hydrochloric acid. There's also always the possibility that it states to use citric acid as it will form a buffer soln in conjunction with its salts.

Actually, after looking at the figures, if you want pH3, you're only going to have to take the most acidic group into account (the other two will be unionized at pH3)

 

[thePrincess69]

Another carbox acid would be vinegar. Acetic Acid.

 

[defaultused]

You can get the necessary concentrations from the Henderson-Hasselbach equation pH = pKa + log([A-]/[HA]). Lets see...3 g citric acid/L is about 0.016 M and 29% HCl is a bit less than 9.45M. So you would need much less HCl than citric acid to achieve the same [H+]. Remember...[A-]/[HA] = Ka/[H+] and pKa = -logKa.

I don't know if that makes sense. I hope for your sake it doesn't.