Anion and Cation Indentification (1 Viewer)

[braindrainedAsh]

Can people please tell me if I what I have here is correct? It comes from what we did in class or tghe conquering chem textbook, is this all I need to know about identifying anions and cations? (see the attached image for the anions)


- barium- flame test- apple/lime green flame. Add fluoride ions, no precipitate is formed. Add NaOH, no precipitate is formed.
- calcium- flame test- brick red flame. Add fluoride ions, a precipitate is formed.
- lead- Add HCl, precipitate is formed.
- copper- Light blue solution. Add NaOH, blue precipitate formed. Flame test- blue/green flame.
- iron (2+)- Add NaOH, blue/grey precipitate formed.
-iron (3+)- Add NaOH, brown precipitate formed. Brown solution.

 

[mitochondria]

that diagram looks like the one in CC.. I'm still not sure why are you posting that picture but.. umm.. it would be handy to know

You see, they can't really ask us to outline a test for certain certain anions and cations - it would be way too... not-HSC if you know what i mean (<-- personal opinion).. If they ever ask you this sort of question they would give you some sort of table that directs you to think which one is a suitable test, e.g. a solubility table.

I personally find testing cations are easier because all you have to do is to choose the right anion to add to it and know some colours (*pretty*) but, yes, if you have extra space in your head i would suggest you to remember that picture.. or you could reversely remember it:

remember that SO4- can be used to test Ba, so this operation can be reversed; or Cl- is added to test to presence of Ag+ so it can also be reversed (note that when AgCl is exposed to light it will be darkened).. The HNO3 and CO3- one is also easy because you know Acid + Carbonate --> salt + water + CO2, so it *bubblez*! (well.. fine.. effervesence)

basically what you have got there is right (the flame tests you can fine them in CC) but i was just curious about the barium one.. if no percipitate is formed, then how do we know that it is present in the solution?

Good luck!


P.S. if you don't have to solubility table.. post a message!

 

[braindrainedAsh]

Yeah the Barium one was a bit iffy, I agree, that was the one I had the main ???? about....

Could you say that you add sulfate ions to test for Ba??? So it's like the reverse? Would that be right? It's just that was all I had in my notes and book, the "no precipitate" ones...

Well the DP says perform first-hand investigations to carry out a range of tests, including flame tests, to identify the following ions... so I think I do need to know them in case they ask how you performed that particular practical task...

 

[mitochondria]

yes, you can say that you add SO4 ions ot test for Ba+ because no matter which way you add them, once they meet in a solution, they aer going to react and form percipitate. However, since SO4(2-) ions is able to form percipitate with various cations, it is actually not right/reliable to use SO4(2-) to test for Ba+ ions.

By saing that they are like reverse of each other was only limited to the case (the picture) in CC. It's just a method of "reversely remembering" things (just to make it.. easier.. but it seemed to have confused you..)

Hmm.. and I have never really come across anything which says the absence of percipitation signifies the presence of another (am i confused? please correct me if i am) - and this actually doesn't work beacuse the absence of percipitate can only suggest the absence of certain ions.

and... hehee... i still don't think they will ever ask *specificly* for a test of certain certain ions... (you see, it is really not possible fo them to ask: "outline a test for the presence of Ag+ ions in a solution".. but i would not be surprised if they ask something like: "outline a test for the presence of Ag+ ions using the provided information/data" or "list the steps for testing a known cations/anions in a solution" <-- this one is dodgy... but i think you get what i mean)

hmm.. after all.. if you really love chem, you should be able to remember them like that *click*.. mee still think it's a good idea to know that picture.. another way to do it is, analyse a solubility table and experiment with it (not with actual chemicals ) then derive your own rules.. could be hard.. but could be fun.. it was meant to be a first-hand investigation anyway

Good Luck!

 

[crazylilmonkee]

Cu + OH-
does that form a precipitate? i thought it formed a blue solution thing

 

[braindrainedAsh]

Well, this was why I was asking!!! I'm not sure, I think it was in my notes...

 

[mitochondria]

hmm.. i've had some problems with geocities *dodgy* i should work now.. try the following link for the solubility table

solubility table

 

[ND]

Originally posted by mitochondria
yes, you can say that you add SO4 ions ot test for Ba+ because no matter which way you add them, once they meet in a solution, they aer going to react and form percipitate. However, since SO4(2-) ions is able to form percipitate with various cations, it is actually not right/reliable to use SO4(2-) to test for Ba+ ions.

As far as the syllabus is concerned, the only anions to precipitate with SO4 are Ba and Ca. Ca will also precipitate with F, but Ba will not. So to test for Ba, add SO4, then F. If it precipitates with SO4 and not F, its Ba.

 

[braindrainedAsh]

Thanks!

 

[ND]

Originally posted by mitochondria

and... hehee... i still don't think they will ever ask *specificly* for a test of certain certain ions... (you see, it is really not possible fo them to ask: "outline a test for the presence of Ag+ ions in a solution".. but i would not be surprised if they ask something like: "outline a test for the presence of Ag+ ions using the provided information/data" or "list the steps for testing a known cations/anions in a solution" <-- this one is dodgy... but i think you get what i mean)

Actually i think they can (and wouldn't be surprised if they did), as we did a first hand investigation into it.

 

[braindrainedAsh]

Yeah in my trial it asked "Outline a test you could do to examine the presence of chloride ions in a solution"

 

[mitochondria]

hmmm... i can bet the "a" of my mitrochondria that they are not going to ask us specificly otherwise, they will have to ask us our results in our experiments.. maybe how much .2M NaCl we used to titrate HCl with unknown concentraion?

umm.. just curious, the trial paper was a school one right?

 

[braindrainedAsh]

I think it was bits and pieces out of lots of different trials, I know the teachers didn't write it.

 

[ND]

Originally posted by mitochondria
hmmm... i can bet the "a" of my mitrochondria that they are not going to ask us specificly otherwise, they will have to ask us our results in our experiments.. maybe how much .2M NaCl we used to titrate HCl with unknown concentraion?

umm.. just curious, the trial paper was a school one right?

They can ask us for our procedure, so you'll have to write which ion you're putting in and why. They also can ask us for results, but they don't have to be quantitative.

 

[mitochondria]

hehee.. i think i've lost my "a"... just saw this thing in the bio section.. they actually askeded for a "scaled" diagram of reb blood cell.. lol, and we are required to know that it is 8um.. sorrry.. but still... chem is easy meee love chem

 

[Constip8edSkunk]

Originally posted by crazylilmonkee
Cu + OH-
does that form a precipitate? i thought it formed a blue solution thing

Cu(OH)2 is a light blue precipitate, upon adding ammonia a deep blue complex forms: Cu(NH3)4 2+ i think it was...
Or right from the beginning, add NH4OH to the sample

Originally posted by braindrainedAsh
Yeah in my trial it asked "Outline a test you could do to examine the presence of chloride ions in a solution"

I think that if you wrote 'add silver nitrate, formation of a white precipitate that turns purple/grey upon exposure to UV light indicates the presence of Cl- ions' would b good


Also i think the syllabus is more inclined to use the ions tests to examine solubility rules rather than individual ion tests.

 

[Dangar]

Do we have to know the solubility table?? Or do you think they will give us the relevant rules in any questions they ask? And what about indicators as well...do we need to know the range of each individual indicator like bromothymol blue or do you think they would give us that info in the exam question as well?

 

[mitochondria]

lol.. i don't think you are required to know the solubility table, and as you have said, if they ever ask you a solubility question they would give you the relevant information needed... however, i'm not saying that you don't have to know it AT ALL, as we've discussed above, you are expected to know specificly about something in the HSC, and testing anions and cations are closely related to the solubility rules

and indicators.. hehee.. they are easy to remember and well.. i've seen some questions (can't remember trials or HSCs) related to indicators and their colour change range, and there are two dot points, one on the left and one on the right in 9.3.1, that specificly asks you about indicators, so i expect that they can ask you about the colour change of indicators, usually as part of a questions (e.g., suggest a suitable indicator.. blah blah blah..)

Hint: their names pretty much tell you what they do
Hint: remember your pracs

good luck!

 

[Constip8edSkunk]

solubility laws was in my school's prac tests, and i think there was 1 or 2 questions in our trial, cut and pasted from NEAP....

besides all u have to know for the hsc is group1 cations r soluble, and rules + exceptions for SO4 Cl NO3 PO4 and CO3 and maybe OH

 

[mitochondria]

have a look @ the solubility table i've posted in my third message in this thread.. hehee.. that's the best solubility table i've ever seen.. still haven't figured out where it comes form, all i know is i keep getting it since year 9.. but it's good

has anyone got a better solubility? those on the net are dodgy... *looking for a neeeeeew one* oops.. might need to ditch the old one if i do find one..