1. Observe the colour of the gas 2. Conduct a litmus test (both blue and red) 3a. Perform an acidified potassium permanganate(VII) test 3b. Perform a splint test 4. Perform a limewater test

Chapter 2 - Qualitative Analysis Flashcards by Zheting Zhang

Test for gases

Observe the colour of the gas
Conduct a litmus test (both blue and red)
3a. Perform an acidified potassium permanganate(VII) test
3b. Perform a splint test
Perform a limewater test

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Hydrogen, H2

Colourless, odourless.
Light splint is extinguished with a ‘pop’ sound.
(No change observed for litmus test.)

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Oxygen, O2

Colourless, odourless.
Glowing splint is rekindled/relit.
(No change observed for litmus test.)

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Carbon dioxide, CO2

Colourless, odourless. 
White ppt (calcium carbonate) is produced when gas is bubbled into limewater (calcium hydroxide).
Moist blue litmus turns red.

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Chlorine, Cl

Greenish-yellow, pungent.

Moist blue litmus turns red, and is then bleached white.

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Sulfur dioxide, SO2

Colourless, pungent.
Acidified potassium manganate(VII), KMnO4, turns from purple to colourless (decolourised).
Moist blue litmus turns red.

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Ammonia, NH3

Colourless, pungent.
White fumes of NH4Cl are observed when a glass rod dipped in concentrated hydrochloric acid is brought near the gas.
Moist red litmus turns blue.

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Water vapour, H2O

Colourless, odourless.
Anhydrous cobalt(II) chloride, CoCl2, paper turns from blue to pink.

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Hydrogen chloride, HCl

Colourless, pungent.
White fumes of NH4Cl are observed when a glass rod dipped in aqueous ammonia is brought near the gas.
Moist blue litmus turns red.

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Test for water

Add a few drops of the sample to anhydrous copper(II) sulfate. Anhydrous CuSO4 changes from white to blue.

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Zn2+ in sodium hydroxide

White precipitate soluble in excess sodium hydroxide to give colourless solution

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Zn2+ in aqueous ammonia

White precipitate soluble in excess aqueous ammonia to give colourless solution

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Al3+ in sodium hydroxide

White precipitate soluble in excess sodium hydroxide to give colourless solution

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Al3+ in aqueous ammonia

White precipitate insoluble in excess aqueous ammonia

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Pb2+ in sodium hydroxide

White precipitate soluble in excess sodium hydroxide to give colourless solution

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Pb2+ in aqueous ammonia

White precipitate insoluble in excess aqueous ammonia

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Ca2+ in sodium hydroxide

White precipitate insoluble in excess sodium hydroxide

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Ca2+ in aqueous ammonia

No precipitate (in aqueous ammonia)

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Cu2+ in sodium hydroxide

Blue precipitate insoluble in excess sodium hydroxide

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Cu2+ in aqueous ammonia

Blue precipitate soluble in excess aqueous ammonia to give dark blue solution

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Fe2+ in sodium hydroxide

Green precipitate insoluble in excess sodium hydroxide

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Fe2+ in aqueous ammonia

Green precipitate insoluble in excess aqueous ammonia

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Fe3+ in sodium hydroxide

Reddish-brown precipitate insoluble in excess sodium hydroxide

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Fe3+ in aqueous ammonia

Reddish-brown precipitate insoluble in excess aqueous ammonia

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NH4+ in sodium hydroxide

No precipitate observed (in sodium hydroxide)

NH4+ in aqueous ammonia

A colourless, pungent gas evolved, which turns moist red litmus blue. Gas is ammonia.

How to differentiate white ppt of Pb2+ and Al3+?

Add potassium iodide (KI): - no precipitate → Al3+ - yellow precipitate (PbI2) → Pb2+

Na+ flame test

Dark yellow

Ba2+ flame test

Pale green

Ca2+ flame test

Red

K+ flame test

Lilac

Pb2+ flame test

Greyish white

Cu2+ flame test

Bluish green

How to produce hydrogen gas?

Acid with reactive metal reaction

How to produce oxygen gas?

Heating of nitrates | Decomposition of hydrogen peroxide

How to produce sulfur dioxide gas?

Reacting dilute acids with sulfite | Heating of sulfates

How to produce chlorine gas?

Hydrochloric acid with oxidising agents

How to produce ammonia gas?

Heating ammonium salts with bases

How to produce carbon dioxide gas?

Heating of carbonates | Reaction of dilute acids with carbonates / hydrogencarbonates

Effect of heat on carbonate (solid)

Generally decompose on strong heating to produce carbon dioxide gas

Effect of heat on Group 1 nitrate (solid)

Decompose on strong heating to produce oxygen gas and the Group 1 metal nitrite

Effect of heat on other nitrates (solid)

Decompose on strong heating to produce oxygen gas and nitrogen dioxide gas (nitrogen dioxide is orange/brown in colour)

Effect on heat on ammonium salt (solid)

Sublime on heating. White solid will be observed on the cooler regions of the test tube.

Effect of heat on hydrated salt (solid)

Produces steam on strong heating. Steam will condense on the cooler regions of the test tube.

NH4+ in aqueous solution

Colourless solution

Na+ in aqueous solution

Colourless solution

K+ in aqueous solution

Colourless solution

Ca2+ in aqueous solution

Colourless solution

Pb2+ in aqueous solution

Colourless solution

Al3+ in aqueous solution

Colourless solution

Cu2+ in aqueous solution

Blue solution

Fe2+ in aqueous solution

Pale green solution

Fe3+ in aqueous solution

Yellow solution

MnO4- in aqueous solution

Purple solution

Mn2+ in aqueous solution

Pale pink/colourless solution

H2O2 in aqueous solution

Colourless solution

Cr2O72- (dichromate) in aqueous solution

Orange solution

Cr3+ in aqueous solution

Green solution

AgCl in aqueous solution

White precipitate

PbCl2 in aqueous solution

White precipitate

AgI in aqueous solution

Yellow precipitate

PbI2 in aqueous solution

Yellow precipitate

CaSO4 in aqueous solution

White precipitate

BaSO4 in aqueous solution

White precipitate

PbSO4 in aqueous solution

White precipitate

CaCO3 in aqueous solution

White precipitate

CuCO3 in aqueous solution

Green solid (due to the malachite mineral)

Cu(OH)2 in aqueous solution

Blue precipitate

Fe(OH)2 in aqueous solution

Dirty-green precipitate

Fe(OH)3 in aqueous solution

Reddish-brown precipitate

CaO(s) appearance

White solid

PbO(s) appearance

Yellow solid

CuO(s) appearance

Black solid

MnO2(s) appearance

Black solid

ZnO(s) appearance

``` White solid (when cooled) Yellow solid (when heated) ```

NO2(g) appearance

Reddish-brown gas

Br2(g) appearance

Reddish-brown gas

Cl2(g) appearance

Greenish-yellow / Yellowish-green gas

I2(g) appearance

Violet gas

I2(s) appearance

Black solid

I2 in aqueous solution

Brown solution

Cu(s) appearance

Pink (fresh) | Reddish-brown (exposed to air)

All metals except Cu(s) appearance

Silver (fresh) | Grey (exposed to air)

Fe(s), Ni(s) appearance

Grey