Titration - Prac assessment -URGENT (1 Viewer)

[JuliaGulia07]

I have a prac assessment to find the concentration (or amount...im not sure, but i guess that doesnt matter) of oxalic acid.

Basically we were told to put oxalic acid in the conical flask and add excess sodium hydroxide so that the solution becomes basic. We add indicator and titrate with hydrochloric acid.

All i remember in class was that...
oxalic acid + hydrochloric acid = sodium hyxoride
therefore ...oxalic acid = sodium hydroxide - hydrochloric acid

the teacher obviously didnt make it clear...does that mean that to get the concentration of the oxalic acid you have to subtract the concentration of HCl from NaOH? i'm confused about what that means....

I would appreciate any help!!
thanks

 

[Forbidden.]

You mean the H⁺ (hydrogen ion / proton) concentration ?
Adding another acid only lowers the pH or rather make it more acidic, you can't combine two acids making them basic.

 

[JuliaGulia07]

You mean the H⁺ (hydrogen ion / proton) concentration ?
Adding another acid only lowers the pH or rather make it more acidic, you can't combine two acids making them basic.

I just did the prac then so its ok. But what is meant by that is that to work out the concentration of the oxalic acid, you must subtract the concentration of the HCl from the NaOH...

n(C₂O₄H₂) = n(NaOH) - n(HCl)

the point of this whole thing is because you can't put a base in the burette, so you have to add the base to the acid you're trying to find, then work out the difference.

 

[Forbidden.]

I just did the prac then so its ok. But what is meant by that is that to work out the concentration of the oxalic acid, you must subtract the concentration of the HCl from the NaOH...

n(C₂O₄H₂) = n(NaOH) - n(HCl)

the point of this whole thing is because you can't put a base in the burette, so you have to add the base to the acid you're trying to find, then work out the difference.

Yes, there are reasons why you can't use NaOH, HCl or H₂SO₄
as a primary standard

Spoiler

NaOH - Deliquesent, meaning it absorbs moisture - Will cause a change in mass/volume

HCl & H₂SO₄ - Molarity differs from batch to batch

 

[JuliaGulia07]

Yes, there are reasons why you can't use NaOH, HCl or H₂SO₄
as a primary standard

Spoiler

NaOH - Deliquesent, meaning it absorbs moisture - Will cause a change in mass/volume

HCl & H₂SO₄ - Molarity differs from batch to batch

lol yeah i know, the point of adding the NaOH wasn't cause it couldnt be used as a primary standard, it was used to make the solution basic, so that we could then use HCl as a titre.

have you guys done this sort of thing at your school yet?

 

[Mohit7]

Ok basically u have your concentration of the first solution and you have the volume of the 1st solution aswell. Then what you do is that once you have titrated, you have found the volume of the 2nd solution and you need to find the concentration of the 2nd solution.

If I am on the right track tell me then i will help further

 

[JuliaGulia07]

Ok basically u have your concentration of the first solution and you have the volume of the 1st solution aswell. Then what you do is that once you have titrated, you have found the volume of the 2nd solution and you need to find the concentration of the 2nd solution.

If I am on the right track tell me then i will help further

yeah, thats it! i've already done it, although i got it wrong so i dont know what i did wrong. we knew the volume and concentration of NaOH, and the concentration of HCl and we had to titrate to find the volume of HCl so that we could work out the concentration and then the mass of the sample of oxalic acid. does that make sense? thanks for the help in advance

 

[xiao1985]

You mean the H⁺ (hydrogen ion / proton) concentration ?
Adding another acid only lowers the pH or rather make it more acidic, you can't combine two acids making them basic.

something curious:

pH 1 HCl (50mL) is added with pH5 HCl (50 mL) you end up with something like pH 2.5 (i didn't do the actual calculation, but it's close enough i guess)

so you can actually increase your pH by adding an other acid =p