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A-level Chem > Qualitative analysis > Flashcards

Qualitative analysis Flashcards

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1
Q

Reagent for carbonate test

A

Any acid

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2
Q

Products for carbonate test with acid

A

Carbon dioxide and water

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3
Q

Observation for carbonate test

A

Effervesence (CO2(g))

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4
Q

To confirm the gas is carbon dioxide…

A

…bubble through limewater.

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5
Q

What is limewater?

A

A saturated solution of calcium hydroxide, Ca(OH)2(aq).

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6
Q

Carbon dioxide and limewater reaction products

A

White precipitate of calcium carbonate (CaCO3)

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7
Q

BaSO4 in water is very…

A

…insoluble.

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8
Q

Reagent used in sulfate test

A

Soluble barium compound, e.g; Ba(NO3)2(aq)

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9
Q

Reagent for halide test

A

Acidified silver nitrate solution: AgNO3(aq)

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10
Q

Ionic equ between chloride and silver nitrate

A

Ag+(aq) + Cl-(aq) …. AgCl(s)

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11
Q

Colour of precipitate for chloride and silver nitrate reaction

A

White

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12
Q

Solubility of AgCl(s) in NH3(aq)

A

Soluble in dilute NH3(aq)

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13
Q

Ionic equ between bromide and silver nitrate

A

Ag+(aq) + Br-(aq) …. AgBr(s)

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14
Q

Colour of precipitate for bromide and silver nitrate reaction

A

Cream

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15
Q

Solubility of AgBr(s) in NH3(aq)

A

Soluble in concentrated NH3(aq)

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16
Q

Ionic equ between iodide and silver nitrate

A

Ag+(aq) + I-(aq) …. AgI(s)

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17
Q

Colour of precipitate for iodide and silver nitrate reaction

A

Yellow

18
Q

Solubility of AgI(s) in NH3(aq)

A

Insoluble on concentrated NH3(aq)

19
Q

Sequence of tests

A
  1. Carbonate test: CO3^2-
  2. Sulfate test: SO4^2-
  3. Halide test: Cl-, Br-, I-
20
Q

Only carbonate produce…

A

…bubbles of gas wen an acid is added.

21
Q

What is expected when Ba^2+(aq) ions are added?

A

A white precipitate of barium sulfate will form, if SO4^2(aq) ions are present.

22
Q

Describe a false positive for the sulfate test

A

If carbonate ions are present, a white precipitate of barium carbonate, BaCO3(s), will form as it is also soluble. This is a flase positive.

23
Q

What is expected when Ag+(aq) are added to a halide solution?

A

A precipitate of a silver halide is expected.

24
Q

What happens if a carbonate or sulfate are present in a halide test?

A

A precipitate will be seen as CO3^2- and SO4^2- are also insoluble.

25
Q

Describe the carbonate test

A

Add any acid until effervesence stops. Effervesence shows carbonate present. Adding the acid to excess removes the carbonate prior to the sulfate test.

26
Q

Why is acid added in excess during the carbonate test?

A

To remove all the carbonate prior to the sulfate test.

27
Q

Describe the sulfate test

A

Add barium nitrate,. Any white precipitate formed (indicating the presence of a sulfate) should be removed via filtration.

28
Q

Describe the halide test

A

Add silver nitrate solution. A precipitate will form if a halide is present. Add ammonia solution to confirm which halide it is.

29
Q

Reagent to test for ammonium- NH4+

A

Sodium hydroxide, NaOH(aq)

30
Q

Describe the test for identifying ammonium

A

Heat aqueous ammonium ions and aqueous hydroxide ions together as they will react to form ammonia gas, NH3(g).

31
Q

Obs for ammonium test

A

Ammonia gas is produced which turns damp red litmus paper blue.

32
Q

Ionic equ for ammonium test

A

NH4+(aq) + OH-(aq) …. NH3(g) + H2O(l)

33
Q

Colour of copper II (Cu2+) solution

A

Blue

34
Q

Colour and formula of copper II (Cu2+) precipitate

A

Light blue
Cu(OH)2(s)

35
Q

Colour of iron III (Fe3+) solution

A

Pale yellow (pale violet)

36
Q

Colour and formula of Fe3+ precipitate

A

Rusty brown
Fe(OH)3(s)

37
Q

Colour of iron II Fe2+ solution

A

Pale green

38
Q

Colour and formula of Fe2+ precipitate

A

Green, goes orange/brown when exposed to air.
Fe(OH)2(s) / Fe(OH)3(s)

39
Q

Colour of maganese II Mn2+ solution

A

Very pale pink, virtually colourless

40
Q

Colour and formula of Mn2+ precipitate

A

Pale brown. Surface darkens on exposure to air.
Mn(OH)2(s) / Mn(OH)3(s)

41
Q

Colour of chromium III Cr3+ solution

A

Green

42
Q

Colour and formula of Cr3+ precipitate

A

Green/grey. Dissolves in excess to form green solution.
Cr(OH)3(s) / [Cr(OH)6]^3-(aq)

A-level Chem (30 decks)

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