Chemistry- Test for ions, gases and other compounds

Sparz By Sparz, 18th Dec 2010 | Follow this author | RSS Feed | Short URL http://nut.bz/1q34oy6m/
Posted in Wikinut>Guides>Science>Chemistry

Some simple tests for various gases and ions. Trust me, they'll come in handy for chemistry tests and exams.
NOTE: I will not be adding more to this page anymore. But i will update the info.

Test for gases

  • Oxygen gas: (O2)
  • It relights a glowing splinter. We can use a glowing splinter for the purpose which is rekindled on contact with oxygen. Oxygen supports burning.

  • Hydrogen gas: (H2)
  • It burns with a squeaky "pop" sound. We can bring a burning splinter in contact with the gas.

  • Carbon dioxide gas: (CO2)
  • When bubbled through lime water it turns the lime water milky.
    This is because it produces calcium carbonate (CaCO3) which has a milky colour.

    Ca(OH)2 + CO2 --> CaCO3 + H2O
    Lime water + Carbon dioxide --> Calcium carbonate (milky colour) + Water

    We must avoid bubbling too much through lime water, otherwise it will give us a clear solution of calcium bicarbonate, making us think the gas isn't carbon dioxide.

    Ca(OH)2 + CO2 --> CaCO3 + H2O

    CaCO3 + H2O + CO2 --> Ca(HCO3)2
    Calcium carbonate + Water + Carbon dioxide --> Calcium bicarbonate (Colourless)

  • Sulphur dioxide gas: (SO2)
  • It bleaches moist flowers. We can place some moist flowers in contact with the gas and see them become bleached.
    Sulphur dioxide turns KMnO4 solution from purple to colourless.
    Sulphur dioxide also turns K2Cr2O7 solution from orange to green.

  • Chlorine gas: (Cl2)
  • It turns moist blue litmus paper pink and then bleaches it.

    H2O + Cl2 --> HCl + HOCl
    Water + Chlorine gas --> Hydrogen chloride (turns blue litmus paper red) + HOCl

    HOCl --> HCl + [O]
    HOCl --> Hydrogen chloride + Atomic oxygen (bleaches red litmus paper)

  • Hydrogen chloride gas: (HCl)
  • It turns blue litmus paper red.
    It also reacts with ammonia gas to produce a white precipitate of ammonium chloride.

    NH3 (g) + HCL (g) --> NH4Cl (s)
    Ammonia gas + hydrogen chloride gas --> Ammonium chloride (white solid)

    Also, if we expose hydrogen chloride gas to moist air it will produce misty fumes, which are tiny droplets of hydrochloric acid.

  • Nitrogen dioxide gas: (NO2)
  • It turns blue litmus paper red.
    It is also brown in colour.

  • Ammonia gas: (NH3)
  • It is the only gas which turns moist red litmus paper blue.
    It also reacts with hydrogen chloride gas to produce a white precipitate of ammonium chloride.

    NH3 (g) + HCL (g) --> NH4Cl (s)
    Ammonia gas + hydrogen chloride gas --> Ammonium chloride (white solid)

  • Nitrogen gas: (N2)
  • It is an almost inert gas and thus can be identified by the lack of reactivity, confirmed indirectly.

Colour of gases

A few gases and their colours:

  • Flourine gas (F2) --> yellow
  • Chlorine gas (Cl2) --> greenish yellow
  • Nitrogen dioxide gas (NO2) --> brown
  • Sulphur dioxide gas (SO2) --> colourless
  • Carbon dioxide gas (CO2) --> colourless
  • Nitrogen monoxide gas (NO) --> colourless
  • Carbon monoxide gas (CO) --> colourless
  • Ammonia gas (NH3) --> colourless
  • Nitrogen gas (N2) --> colourless
  • Oxygen gas (O2) --> colourless

Test for pure water

Physical test:
Pure water freezes at 0C and boils at 100C.

Chemical test:

  1. Water turns anhydrous copper(II)sulphate from white to blue.

  2. CuSO4 + 5H2O --> CuSO4.5H2O
    Anhydrous copper(II)sulphate (white) + water --> Hydrated copper(II)sulphate (blue)

  3. Water also turns anhydrous cobalt(II)chloride from blue to pink.

  4. CoCl2 + 6H2O --> CoCl2.6H2O
    Anhydrous cobalt(II)chloride (blue) + water --> Hydrated cobalt(II)chloride (pink)

Flame tests for Cations

We first take a wire of nickel or platinum and dip it into hydrochloric acid solution and place it in the flame, so that all the impurities are burnt away. Then the wire is dipped into hydrochloric solution once again and the salt whose cation is to be conformed. This wire is then placed in a flame and the colours produced are observed.
The following are some cations and their flame colours:

  • Sodium ions (Na+) --> Golden yellow
  • Potassium ions (K+) --> Lilac
  • Calcium ions (Ca2+) --> Brick red
  • Barium ions (Ba2+) --> Apple green
  • Lithium ions (Li+) --> Crimson
  • Copper (II) ions (Cu2+) --> Blue green
  • Lead (II) ions (Pb2+) --> Blue
  • Magnesium ions (Mg2+) --> Brilliant white

Test for transition element cations

  • Fe2+ ions: (Iron (II) ions)
  • We add a few drops of NaOH solution to solution suspected to contain Fe2+ ions and if the ions are present a dirty green precipitate of Iron(II)hydroxide is formed.

    Fe2+ + 2OH- --> Fe(OH)2
    Iron(II) ions + hydroxide ions --> Iron(II)hydroxide (dirty green colour)

  • Fe3+ ions (Iron (III) ions)
  • We add a few drops of NaOH solution to solution suspected to contain Fe3+ ions and if the ions are present a brown precipitate of Iron(III)hydroxide is formed.

    Fe3+ + 2OH- --> Fe(OH)3
    Iron(III) ions + hydroxide ions --> Iron(III)hydroxide (brown colour)

  • Cu2+ ions (Copper (II) ions)
  • We add a few drops of NaOH solution to solution suspected to contain Cu2+ ions and if the ions are present a blue precipitate of Copper(II)hydroxide is formed.

    Cu2+ + 2OH- --> Cu(OH)2
    Copper(II) ions + hydroxide ions --> Copper(II)hydroxide (blue colour)

Test for other cations

  • Zn2+ ions (Zinc (II) ions)
  • We add a few drops of NaOH solution to solution suspected to contain Zn2+ ions and if the ions are present a white gelatinous precipitate of Zinc(II)hydroxide is formed.

    Zn2+ + 2OH- --> Zn(OH)2
    Zinc(II) ions + hydroxide ions --> Zinc(II)hydroxide (white gelatinous colour)

    But we must be careful as this white gelatinous precipitate dissolves in excess NaOH solution to give a clear solution.

    Zn(OH)2 + 2OH- --> [Zn(OH)4]2-
    Zinc(II)Hydroxide (white) + hydroxide ions --> Zincate ion (clear)


  • NH4+ ions (Ammonium ions)
  • We add a few drops of NaOH solution to solution suspected to contain ions. A gas (NH3 - Ammonia gas) given off which turns red litmus paper blue and also reacts with HCl gas to produce white fumes of NH4Cl, proves its presence.

    NH4+ + OH- --> H2O + NH3 + {Salt}
    Ammonium ion + Hydroxide ion --> Water + Ammonia gas + (Salt)

    NH3 + HCl --> NH4Cl
    Ammonia gas + Hydrogen chloride gas --> Ammonium chloride (white solid)

    For example if we add NaOH to a solution of NH4Cl (Ammonium chloride) this is the reaction:
    NH4Cl + NaOH --> NaCl + H2O + NH3
    Ammonium chloride + Sodium hydroxide --> Sodium chloride (salt) + Water + Ammonia gas


  • Al3+ ions (Aluminium ions)
  • We add a few drops of NaOH solution to solution suspected to contain Al3+ ions and if the ions are present a white gelatinous precipitate of Alumininm hydroxide is formed.

    Al3+ + 2OH- --> Al(OH)3
    Aluminium ions + hydroxide ions --> Aluminium hydroxide (white gelatinous colour)

    But we must be careful as this white gelatinous precipitate dissolves in excess NaOH solution to give a clear solution.

    Al(OH)3 + 2OH- --> [Al(OH)4]-
    Aluminium Hydroxide (white) + hydroxide ions --> Aluminate ion (clear)

Colour of solids

The following are some solids and their colours:

  • Iodine --> shiny black
  • Sulphur --> yellow
  • Copper(II)oxide --> black
  • Copper(I)oxide --> red
  • Fe2+ salts --> green
  • Fe3+ salts --> brown
  • Cu2+ salts --> blue

Test for anions

  • (CO3)2- ions (Carbonate ions)
  • We add a dilute acid to the solution suspected to contain (CO3)2- ions. A gas (carbon dioxide) is liberated which turns lime water milky proves the presence of these ions.

    CaCO3 + 2HCl --> CaCl2 + H2O + CO2
    Calcium carbonate + Dilute hydrochloric acide --> Calcium chloride + Water + Carbon dioxide

    CO2 + Ca(OH)2 --> CaCO3 + H2O
    Carbon dioxide + Lime water --> Calcium carbonate (milky colour) + water

  • Cl- ions (Chloride ions)
  • We add Silver nitrate (AgNO3) to the solution suspected to contain Cl- ions. A white precipitate of silver chloride (AgCl) is formed confirming the presence of the ions.

    Cl- + Ag+ --> AgCl
    Chloride ions + silver ions --> silver chloride (White)

    [Nitric acid (HNO3) is also added to the solution to get rid (CO3)2- or (SO3)2- so they don't interfere with the reaction as they may react with the silver ions.]

  • Br- ions (Bromide ions)
  • We add Silver nitrate (AgNO3) to the solution suspected to contain Br- ions. A pale yellow precipitate of silver bromide (AgBr) is formed confirming the presence of the ions.

    Br- + Ag+ --> AgBr
    Bromide ions + silver ions --> silver bromide (pale yellow)

    [Nitric acid (HNO3) is also added to the solution to get rid (CO3)2- or (SO3)2- so they don't interfere with the reaction as they may react with the silver ions.]

  • I- ions (Iodide ions)

  • We add Silver nitrate (AgNO3) to the solution suspected to contain I- ions. A bright yellow precipitate of silver iodide (AgI) is formed confirming the presence of the ions.

    I- + Ag+ --> AgI
    Iodide ions + silver ions --> silver iodide (bright yellow)

    [Nitric acid (HNO3) is also added to the solution to get rid (CO3)2- or (SO3)2- so they don't interfere with the reaction as they may react with the silver ions.]

  • (SO3)2- and (SO4)2- ions (Sulphite and Sulphate ions respectively)
  • We add a few drops of Barium chloride (BaCl2) solution to the solution suspected to contain the ions. Both sulphate and sulphite ions produce a white precipitate proving the presence of the ion.

    BaCl2 + (SO3)2- --> BaSO3 + 2Cl-
    Barium chloride + sulphite ion --> Barium sulphite (white) + Chloride ions

    BaCl2 + (SO4)2- --> BaSO4 + 2Cl-
    Barium chloride + Sulphate ions --> Barium sulphate (white) + chloride ions

    In order to distinguish between Sulphite (SO3)2- and Sulphate (SO4)2- ions we add dilute hydrochloric acid (HCl) to the white precipitate formed. Barium sulphite (BaSO3) will dissolve in the acid but Barium sulphate (BaSO4) will not.

    BaSO3 + 2HCl --> Bacl2 + H2O + SO2
    BaSO4 + 2HCl --> No reaction

Test for Iodine (I2)

We add a few drops of starch solution and if Iodine is present, we get a blue black solution of starch iodine complex.

Tags

Anions, Cations, Chemical Tests, Chemistry, Experiments, Flame Tests, Gases, Ions, Physical Tests, Tests

Meet the author

author avatar Sparz
Well writing hasn't been one of my best playing fields but i guess theres always a first. I will try my best and provide articles of detail and worth. Hope you like em ! :]

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Comments

author avatar Denise O
21st Dec 2010 (#)

Good info.
Thank you for sharing.:)

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author avatar Sparz
21st Dec 2010 (#)

Any time Denise O

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author avatar D in The Darling
22nd Dec 2010 (#)

Hey, this is something else!
You're amazing. This is great. Thanks for sharing!

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author avatar Sparz
22nd Dec 2010 (#)

Your welcome dinthedarling. Hope they help

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author avatar ppruel
24th Dec 2010 (#)

informative sharing dude. thanks.

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author avatar Sparz
24th Dec 2010 (#)

No prob ppruel.

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author avatar SiddiQ
1st Jan 2011 (#)

Happy New Year, sharky!!!!

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author avatar Greenfaol
4th Jan 2011 (#)

It does my heart good to see some very cool chemistry. Thanks for that. love the profile pic, I'm a naruto fan :D

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author avatar Sparz
5th Jan 2011 (#)

A very happy new year to you and everyone else who supported me and helped me so far :]

@Greenfaol: thank you so much and yes so far naruto is kinda my favourite anime/mange :D
Chemistry has been a weakness to me and i don't want others to have problems like me. Hope it really helps!

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author avatar Sparz
5th Jan 2011 (#)

Again thank you so very much and a happy happy new year!

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author avatar Michelle
7th Jan 2011 (#)

nothing about precipitates
dissapointed!!!!

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author avatar Kenneth oroke
5th Apr 2011 (#)

this is a good job pls. keep it up.

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author avatar M.Madhukumar
17th Apr 2011 (#)

Why we add NaOH to salt in test for NH4 ion?

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author avatar Sparz
22nd May 2011 (#)

@Michelle: Well the precipitates formed are what we use to recognize the ions etc :/

@Kenneth oroke: Thanks but real credit goes to my teacher for giving these to us in the first place :)

@M.Madhukumar: The OH- ions react with the NH4+ ions to produce ammonia (NH3) and water (H2O) and a salt.
(Sorry my description was not clear but i've changed it) :)

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author avatar Rizz
25th Jun 2011 (#)

thanks. Really good info regarding tests for respective gases cations anion ecc. Found this very helpful.

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author avatar Sparz
9th Oct 2011 (#)

Your welcome rizz :D

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author avatar Vicky
21st Mar 2012 (#)

Wow!!! A nice info!!! I got nearly all the informations I needed but can you please add more common elements at least for exam purposes.

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author avatar Sparz
30th Mar 2012 (#)

Sure vicky, just tell me what you want and i'll see what i can do :)

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author avatar Riley
14th Apr 2012 (#)

what about for nitrate and thiocyanate ions?

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author avatar Sparz
16th Apr 2012 (#)

Hmm, ill try adding those in my free time, thanks for telling me Riley :)

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author avatar Xsx
2nd May 2012 (#)

You put Zn under transition metals, zinc is not a transition metal as it has only one oxidation state....
Just saying :)

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author avatar Xsx
2nd May 2012 (#)

Oh it says transition and metal :P
anyway this was very helpful and easy to learn (Y)

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author avatar Sparz
6th May 2012 (#)

oh my bad ty for pointing that out Xsx :D I put zinc under that title cuz it comes late in the first row of transition elements, but yea your right its not one so ill have that fixed. Thanks again :)

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author avatar Geniva Ba Mzondile
22nd Oct 2012 (#)

i only wnt to knw about the unknwn code

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author avatar Abhishek Saini
10th Feb 2013 (#)

I think this will surely help in my practicals.thanks bro......

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author avatar Sparz
20th Feb 2013 (#)

no problem, happy to help :)

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author avatar 27
12th Mar 2014 (#)

Might be nice to have definition of anion with it too for those just learning... just saying, other than that great help

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author avatar 27
12th Mar 2014 (#)

At first I didn't know but pieced it together by ions shown

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author avatar Ruskie
30th Apr 2014 (#)

Thanks man, this is really useful for my chemistry exam, im very grateful.

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author avatar Anselm
17th Jun 2014 (#)

This is fantastic

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author avatar Penda jude
17th May 2015 (#)

It's good but the test for Al3+ and Zn2+ should be revisited so as to ascertain a clear cut difference

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