5 QUALITATIVE ANALYSIS (QA) Flashcards
What salts
Colour of solid : white
Colour of aqueous salt solution : colourless
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Sodium potassium calcium magnesium aluminium zinc ammonia
What salts
Colour of solid : blue
Colour of aqueous salt solution : blue
- CuSO₄: Copper(II) sulfate
- Cu(NO₃)₂: Copper(II) nitrate
What salts
Colour of solid : greeen
Colour of aqueous salt solution :blue
CuCl₂: Copper(II) chloride
What salts
Colour of solid : green
Colour of aqueous salt solution ; insoluble
CuCO₃: Copper(II) carbonate
What salts
Colour of solid : green
Colour of aqueous salt solution : green
FeSO4, Fe(NO3)2, FeCl2
Iron sulfate
Iron nitrate
Iron chloride
What salts
Colour of solid : brown
Colour of aqueous salt solution : yellow
Fe₂(SO₄)₃ (iron(III) sulfate),
Fe(NO₃)₃ (iron(III) nitrate),
FeCl₃ (iron(III) chloride).
What salts
Colour of solid : brown when hot and yellow when cold
Colour of aqueous salt solution : insoluble
- PbO: Lead(II) oxide
What salts
Colour of solid : black
Colour of aqueous salt solution : insoluble
- CuO: Copper(II) oxide
What salts
Colour of solid : yellow when hot and white when cold
Colour of aqueous salt solution : insoluble
- ZnO: Zinc oxide
What salts
Colour of solid : white
Colour of aqueous salt solution : insoluble in cold water but soluble in hot water to give a colour less solution
- PbCl₂: Lead(II) chloride
What salts
Colour of solid : yellow
Colour of aqueous salt solution : insoluble in cold water but soluble in hor water to give a colour less solution
- PbI₂: Lead(II) iodide
All metal hydroxides, except for which grp hydroxides, are insoluble?
grp 1
how to test for cations Ca2+, Zn2+, Al3+, Pb2+, Fe2+, Fe3+,Cu2+ , NH4
Reagent (NaOH(aq) / NH3(aq)) must be added drop-wise, then in excess. If precipitate forms, the colour of precipitate must be noted and the solubility of precipitate in excess alkali must be checked.
all the cations thatt can be tested
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cal zinc alum lead iron3 iron2 copper amm
Ca2+ -> NaOH(aq) tests reactions
dropwise: white ppt formed
excess: white ppt insoluble in excess
Zn2+ -> NaOH(aq) tests reactions
dropwise:white ppt formed
excess:white ppt soluble to give colourless solution
Al3+ -> NaOH(aq) tests reactions
dropwise:white ppt formed
excess:white ppt soluble to give colourless solution
Pb2+ -> NaOH(aq) tests reactions
dropwise:white ppt formed
excess:white ppt soluble to give colourless solution
Fe3+ -> NaOH(aq) tests reactions
dropwise:reddish-brown ppt formed
excess:reddish-brown ppt insoluble in excess
Fe2+-> NaOH(aq) tests reactions
dropwise:green ppt formed
excess:green ppt insoluble in excess
Cu2+ -> NaOH(aq) tests reactions
dropwise:blue ppt formed
excess:blue ppt insoluble in excess
NH4 -> NaOH(aq) tests reactions
dropwise: no ppt formed
excess: NA
cation NaOH memory tech
dropwise: first 4 is white ppt formed, then rgb and no ppt
excess. first insoluble, next 3 white soluble to colourless(ZAP), rest insoluble
Ca2+-> NH3(aq) tests reactions
dropwise: no ppt formed
excess: NA
Zn2+-> NH3(aq) tests reactions
dropwise:white ppt formed
excess:white ppt soluble to give colourless solution
Al3+ -> NH3(aq) tests reactions
dropwise:white ppt formed
excess:white ppt insoluble in excess
Pb2+ -> NH3(aq) tests reactions
dropwise:white ppt formed
excess:white ppt insoluble in excess
NH4 -> NH3(aq) tests reactions
dropwise:no ppt
excess: NA
Fe3+ -> NH3(aq) tests reactions
dropwise:reddish-brown ppt formed
excess:reddish-brown ppt insoluble in excess
Fe2+ -> NH3(aq) tests reactions
dropwise:green ppt formed
excess:green ppt insoluble in excess
Cu2+ -> NH3(aq) tests reactions
dropwise:blue ppt formed
excess: blue ppt soluble to give dark blue solution
y NaOH and NH3 for the tests?
the main point is for the OH-
Na doesnt actl matter its kinda js a carrier for OH-
Aqueous ammonia is a weak alkali that ionizes partially in water to produce a low concentration of OH−
all the testable anions
CO3^2-, Cl-, I-, SO4^2-, NO3-
carbonate chloride iodine sulfate nitrate
how to test for CO3^2- and its observations
test :Add dilute HNO3(aq) or any other mineral acid to 1 cm3 of the unknown. Test the gas evolved using limewater.
observation: Effervescence of a colourless and odourless gas, which gave a white precipitate with limewater.
how to test for Cl- and its observations
test: Add dilute HNO3(aq), followed by aqueous silver nitrate solution.
observation: White precipitate of AgCl (s) was formed.
how to test for I- and its observations
test: Add dilute HNO3(aq), followed by [aqueous silver/aqueous lead (II)] nitrate solution.
observation: Yellow precipitate of AgI (s) or PbI2(s) was formed.
how to test for NO3- and its observations
test: Add (excess) NaOH(aq) followed by aluminium powder/foil. Warm carefully. Test the gas evolved using a damp red litmus paper.
observation: Colourless and pungent gas was evolved which
turned the damp red litmus paper blue. Gas evolved is NH3(g).
u cant actl test for NO3 but if its not ammonia its NO3
how to test for SO4^2- and its observations
test: Add dilute HNO3(aq) followed by aqueous barium nitrate or aqueous barium chloride solution.
observation: White precipitate of BaSO4(s) was formed.
how to test for CO2 gas
test:Test the gas evolved using limewater (Ca(OH)2(aq)).
obvservation: Gas gave a white precipitate with limewater.
how to test for H2 gas
test: Test with a lighted splint.
obvservation: Gas burned with a pop sound.
how to test for Cl2 gas
low chance of coming out
test: Test the gas evolved with damp litmus paper. Gas turned damp blue litmus paper red, before
obvservation: litmus paper is bleached.
how to test for NH3 gas
test:Test the gas evolved with damp red litmus
paper.
obvservation: Gas turned damp red litmus paper blue.
how to test for O2 gas
test: Test with a glowing splint.
obvservation: Gas relights the glowing splint.
how to test for SO2 gas
low chance of coming out
test:
Test gas evolved with either
acidified potassium dichromate (VI), K2Cr2O7(aq).
acidified potassium manganate (VII), KMnO4(aq).
obvservation:
K2Cr2O7 solution changed from orange to
green.
KMnO4 solution changed from purple to
colourless
further test for cations using dilute h2so4 sulfuric acid -?
throw h2so4 into a solution
if a white ppt forms, cations are Ba2+ or Pb2+
(formation of insoluble BaSO4 or PbSO4)
further test for cations using dilute HCl -?
throw HCL into a solution
if a white ppt forms, cation is Pb2+
(formation of insoluble PbCl2)
NOTE: PbCl2 can be crystalised w heating
what else can the dilute sulfurioc and hydrochloric acid tests do
they can differentiate Pb2+ from Al3+. it does this by confirming that the cation is not Al3+ as aluminium dissolves and is Pb2+ as lead forms a ppt
further test for cations using Aq KI
throw Aq KI into a solution
if a yellow ppt forms, cation is Pb2+
if a brown solution + white ppt forms, cation is Cu2+
if a brown solution forms, theres an oxidising agent
redox reaction: the oxidising agent donates electrons to the other(eg. iodine, which forms the brown solu)
2 Cu2+ (aq) + 4 I(aq) Cu2I2 (s) + I2 (aq).
further test for cations using Acidified aq. KMnO4 / Acidified aq. K2Cr2O7
if theres oxidising agents that donate electrons,
KMnO₄: Purple to colorless.
K₂Cr₂O₇: Orange to green.
When green precipitate of iron (II) hydroxide is left in the open for some time, it turns brown. Explain this observation.
The oxygen in the air has oxidized the green iron (II) hydroxide to the brown iron (III) hydroxide.
When aqueous sodium hydroxide is added to aqueous copper (II) nitrate, a blue precipitate is produced. When the mixture is brought to a boil, the blue precipitate turns into a black solid. Explain these observations.
1st half is thhe cation tests
Aqueous copper (II) nitrate reacts with aqueous sodium hydroxide to produce blue precipitate of copper(II) hydroxide.
Cu(NO3)2(aq) + 2NaOH(aq) -> Cu(OH)2(s) + 2NaNO3(aq)
2nd half is seeing the BLACK solid and identifying CuO and heatign is decomposition
When the blue precipitate of copper (II) hydroxide is heated, it decomposes to produce the black copper (II) oxide solid.
Cu(OH)2(s) -> CuO(s) + H2O(g)
