Discussion for deducing ions (1 Viewer)

[Pace_T]

Hello everybody
Sorry for the many questions.. I've finally just got stuck into studying
What are some points I should discuss regarding the reliability and accuracy when deducing ions present in a sample? I've looked everywhere but I can't find much information on this.

Thanks in advance.

 

[currysauce]

which dotpoint are u looking at, cuz the deducing ions doesn't need what ur asking

 

[Pace_T]

but i thought the point was suggesting that we do a practical to deduce ions present (which poeple here have been doing)
and usually there's a discussion when u do pracs
cheers matey

 

[Dreamerish*~]

Something I can think of is distinguishing between two ions which have similar precipitate colours or properties in solution, and therefore the results are not completely reliable.

Take Ca²⁺ and Ba²⁺ for example. Both cations form white precipitates with SO₄^2-. Therefore if white precipitate is formed with Na₂SO₄ solution, a further test is required to identify whether the cation present is Ca²⁺ or Ba²⁺.

Now we would use the flame test. While Ba²⁺ glows apple-green in a flame test, Ca²⁺ glows brick-red. (Refer to my other post on distinguishing ions by flame test: http://www.boredofstudies.org/community/showpost.php?p=1705865&postcount=14 )

Some other factors to consider would be to use a black plastic pallet when testing for precipitates, so that it is easy to see the solid particles, and identify the colour of the precipitate.

I think that's what you were after, are there any specific questions on a particular ion?

 

[currysauce]

i see, you mean this dot point

perform first-hand investigations to carry out a range of tests, including flame tests, to identify the following ions:
- phosphate
- sulfate
- carbonate
- chloride
- barium
- calcium
- lead
- copper
- iron


Then i guess u would

 

[Pace_T]

That's it. Thanks heaps!!

 

[richz]

u need to know all the tests, like precipitation and flame tests..

 

[IcEy]

With the Ba, Ca Dreamerish was talking about.
Instead of testing with flame test, you can add NaF to the solution, since CaF2 is insoluble.

 

[Dreamerish*~]

See below posts.

 

[niall045]

Iron (II) forms green precipitaite with OH^- while iron (III) forms brown.

i hope ur not deadly sure on the iron (II) forming a green precipitate with hydroxide 'cos i read in a few textbooks that it is white. o dear

 

[Dreamerish*~]

i hope ur not deadly sure on the iron (II) forming a green precipitate with hydroxide 'cos i read in a few textbooks that it is white. o dear

Sorry, my bad.

Well iron (II) solution is pale green, and when you add in hydroxide ions the iron (II) hydroxide precipitate that forms is greyish-green - that's the way that most people use, and is pretty accurate in real life.

There you have it.

To distinguish between the two: Fe²⁺ decolourises acidified dilute potassium permanganate solution and Fe³⁺ forms a deep red solution with SCN^-.

 

[azza_3761]

how has everyone else duduced between iron (II) and iron (III)? I'm so confused with these two.

Iron(II) + NaOH --> White precipitate which changes to a brown precipitate
Iron(III) + NaOH --> Brown precipitate

 

[Dreamerish*~]

Iron(II) + NaOH --> Brown precipitate
Iron(III) + NaOH --> White precipitate which changes to a brown precipitate

Other way around.

Iron (III) forms a brown precipitate, and my sources have contradicted each other, but Nit confirmed that the precipitate formed by iron (II) and hydroxide is in fact greyish-green. Refer to my post above with quote.

 

[azza_3761]

Other way around.

Iron (III) forms a brown precipitate, and my sources have contradicted each other, but Nit confirmed that the precipitate formed by iron (II) and hydroxide is in fact greyish-green. Refer to my post above with quote.

Yea thanx for the correction dreamerish