Identifying substances (1 Viewer)

[laurenbrennan]

we need to identfy different substances.. and to cut to the chase, i am having trouble differentiating between barium chloride and sodium sulfate with only the availability of silver nitrate, HCl, NaOH, and universal indicator!
becuase the two have the same pH and both form no precipitate when you add any of those compounds (as far as i am aware)!
if anyone could help out that would be excellent.
ps. not long till i need to do it so asap reply would be amazing thankss

 

[yorkstanham]

im pretty sure barium doesnt form a percipitate with NaOH

 

[Undermyskin]

OK, this should be easy IF you are told that one of them is BaCl and the other is Na2SO4.

Just need to add AgNO3 to the solution and observe: precipitate --> SO4 (2-) is present.

Hang on, I'm not sure when you mean by 'differentiating'. Is it simply identifying or you are supposed to make up these two separate solutions from a mixture?

In your prac, if Ag2SO4 is not formed, it's sort of troublesome. My prac this morning was horrible and I'm still shivering. I suspected a substance to be Cu but then the test with NaOH doesn't even work for the known sample of Cu 2+. Then the flame tests between Ba 2+ and Cu 2+ just messed up. Then I suppose another one to be Ferric or Ferrous. Adding potassium hexanoferrate didn't work either so I add Potassium cyanide to make sure. It didn't work! OMG. Then it turned out to be Pb 2+, I tested by adding KI to it and it formed yellow precipitate. Gosh! It was soooooooo dodgy. (

 

[kooltrainer]

zomg.. too pro man.. how did u know what to add and stuff.. what does ferric or ferrous mean.. whats this cyanide.. ..
are u suppose to like memorise the solubility rules and flame test colours...

 

[Felix Jones]

omg dude go and study, those terms should be familiar to u by now....and for the solubility rules, yes u have to memories...very very important.

 

[Undermyskin]

Agree with Moey. All these should be the fundamental stuff you are supposed to know by now.

The trial experiment last time we did was 'evil'. All the substances we tested fell into the scarce cases. eg. PbSO4 is normally insoluble even in acidic solution, right? But then since the []s of the ions we used were a bit low so it turned out to be soluble! GOSH. Guyz, be careful when testing Pb 'cuz it's really tricky. To make sure, you'd better add KI which always gives you a positve answer.

Can anyone help find way to dissolve Ferric and ferrous sulfates? I tried like the whole test tube full of HNO3 4M with 4 or 5 grains of these stuff but I couldn't dissolve them. We thought it was some problem with the impure substances but when the teacher tested something else, it worked perfectly. (Shit) Helps are appreciated!

To Kool: ferrous - Fe 2+
Ferric - Fe 3+

 

[brenton1987]

whats this cyanide

The CN^- anion.

 

[aussiechick007]

oh my, we started this today... and it wasn't working for me at all! all the things i was heating nothing was happening.... this is a disasterous part of chemistry!

 

[Darrow]

Seriously, the flame tests are so dodgy
The only one that partially worked for me was Cu2+.. but that was still faint
But I have a prac test on this...tuesday.

Have you tried Sodium Hydroxide for the Fe (III) Ions...Fe2(SO4)3 supposed to be soluble in water?
Not so sure on the Fe (II) though..

 

[Undermyskin]

I don't think iron sulfates are insoluble in water since most sulfates are soluble except those of Calcium, barium, Lead, and some other very unreactive metals.

If you're given samples of ferric or ferrous salts, be very careful because your tests can give positive indications to both of them.

eg When I added CN- solution to test Fe3+, both solutions of Ferric and ferrous turn RED! Then I realize I might make some mistakes because HNO3 is quite an oxidizing acid --> oxidize Ferrous ions further to ferric. But when I try again and add potassium ferrocyanate K3Fe(CN)3 or 4 or st, then in both solutions, the green colours turn BLUE! Crap, so basically Ferric and ferrous are BOTH present.

That's why it's unlikely you'll be given salts of iron.