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Pure Chemistry (Sec 3) > Chapter 11 - Qualitative Analysis > Flashcards

Chapter 11 - Qualitative Analysis Flashcards

1
Q

What does qualitative analysis refer to?

A

Salts are ionic compounds which contains cations and anions. You can identify the cations and anions by adding certain reagents to a portion of the salt solution. This process of identifying an unknown substance (cations and anions) is aka QA

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2
Q

What are the 3 things that there are chemical tests to identify?

A

1) Cations
2) Anions
3) Gases

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3
Q

What are the reagents used to identify cations?

A

1) Aqueous sodium hydroxide solution, NaOH (aq)
2) Aqueous ammonia, NH3 (aq)

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4
Q

All cations give precipitates with the alkalis except for ____, ____, ____

A

Na+, K+, NH4+

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5
Q

What factors are used to identify a cation?

A

1) Colour of precipitate produced (if any), when reagent is added
2) Whether the precipitate is soluble or insoluble in excess of the reagent
3) Whether ammonia gas is evolved on the addition of aqueous sodium hydroxide solution

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6
Q

What are the 2 stages for adding NaOH (aq) or NH3 (aq) to a solution containing cations?

A

1) Add a few drops
2) Add excess
* Look out for the colour of precipitate, and whether it dissolves in excess

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6
Q

What are the cations to be identified?

A

1) Aluminium ion, Al^3+
2) Zinc ion, Zn^2+
3) Iron (II) ion, Fe^2+
4) Iron (III) ion, Fe^3+
5) Ammonium ion, NH4+
6) Calcium ion, Ca^2+
7) Copper (II) ion, Cu^2+

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7
Q

What can you observe when you add a few drops of sodium hydroxide, NaOH, to calcium, Ca^2+ ?

A

White precipitate of calcium hydroxide forms, Ca(OH)2
Ca^2+ (aq) + 2OH^- (aq) –> Ca(OH)2 (s)

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8
Q

What can you observe when you add in excess sodium hydroxide, NaOH, to calcium, Ca^2+?

A

White precipitate remained, so its insoluble in excess of NaOH (aq)

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9
Q

What can you observe when you add a few drops of sodium hydroxide, NaOH, to zinc ion, Zn^2+?

A

White precipitate of zinc hydroxide, Zn(OH)2, is formed

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10
Q

What can you observe when you add in excess sodium hydroxide, NaOH, to zinc ion, Zn^2+??

A

White precipitate dissolves to form a colourless solution

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11
Q

What can you observe when you add a few drops of sodium hydroxide, NaOH, to aluminium ion, Al^3+?

A

White precipitate of aluminium hydroxide, Al(OH)3, is formed
Al^3+ (aq) + 3OH^- (aq) –> Al(OH)3 (s)

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12
Q

What can you observe when you add in excess sodium hydroxide, NaOH, to aluminium ion, Al^3+?

A

White precipitate dissolves to form a colourless solution

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13
Q

What can you observe when you add a few drops of sodium hydroxide, NaOH, to iron (II) ion, Fe^2+?

A

Green precipitate of, iron (II) hydroxide, Fe(OH)2 is formed
Fe^2+ (aq) + 2OH^- (aq) –> Fe(OH)2 (s)

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14
Q

What can you observe when you add in excess sodium hydroxide, NaOH, to iron (II) ion, Fe^2+?

A

Green precipitate remains as the precipitate is insoluble in excess. the precipitate turns brown on standing

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15
Q

What can you observe when you add in a few drops of sodium hydroxide, NaOH, to iron (III) ion, Fe^3+?

A

Reddish brown precipitate of, iron (III) hydroxide, Fe(OH)3 formed
Fe^3+ (aq) + 3OH^- (aq) –> Fe(OH)3 (s)

16
Q

What can you observe when you add in excess sodium hydroxide, NaOH, to iron (III) ion, Fe^3+?

A

Reddish brown precipitate remained, as it is insoluble in excess

17
Q

What can you observe when you add in a few drops of sodium hydroxide, NaOH, to copper (II) ion, Cu^2+?

A

Blue precipitate of, Cu(OH)2 formed
Cu^2+ (aq) + 2OH^- (aq) –> Cu(OH)2 (s)

18
Q

What can you observe when you add in excess sodium hydroxide, NaOH, to copper (II) ion, Cu^2+?

A

Blue precipitate remains as precipitate is insoluble in excess

19
Q

What can you observe when you add in a few drops of sodium hydroxide, NaOH, to ammonium ion, NH4+?

A

No precipitate formed
Ammonia gas (NH3) released when heated

20
Q

What can you observe when you add in a few drops of ammonia, NH3, to calcium ion, Ca^2+?

A

No precipitate

21
Q

What can you observe when you add in excess ammonia, NH3, to calcium ion, Ca^2+?

A

No change is observed

22
Q

What can you observe when you add in a few drops of ammonia, NH3, to zinc ion, Zn^2+?

A

White precipitate of zinc hydroxide, Zn(OH)2 is formed
Zn^2+ (aq) + 2OH^- (aq) –> Zn(OH)2 (s)

23
Q

What can you observe when you add in excess ammonia, NH3, to zinc ion, Zn^2+?

A

White precipitate dissolves in excess to form a colourless solution

24
Q

What can you observe when you add in a few drops of ammonia, NH3, to aluminium ion, Al^3+?

A

White precipitate of aluminium hydroxide, Al(OH)3 is formed
Al^3+ (aq) + 2OH^- (aq) –> Zn(OH)2 (s)

25
Q

What can you observe when you add in excess ammonia, NH3, to aluminium ion, Al^3+?

A

White precipitate remained as it is insoluble in excess

26
Q

What can you observe when you add in a few drops of ammonia, NH3, to iron (II) ion, Fe^2+?

A

Green precipitate of iron (II) hydroxide, Fe(OH)2 is formed
Fe^2+ (aq) + 2OH^- (aq) –> Fe(OH)2 (s)

27
Q

What can you observe when you add in excess ammonia, NH3, to iron (II) ion, Fe^2+?

A

Green precipitate remained as it is insoluble in excess. The precipitate turns brown on standing

28
Q

What can you observe when you add in a few drops of ammonia, NH3, to iron (III) ion, Fe^3+?

A

Reddish brown precipitate of iron(III) hydroxide, Fe(OH)3 formed
Fe^3+ (aq) + 3OH^- (aq) –> Fe(OH)3 (s)

29
Q

What can you observe when you add in excess ammonia, NH3, to iron (III) ion, Fe^3+?

A

Reddish brown precipitate remained as it is insoluble in excess

30
Q

What can you observe when you add in a few drops of ammonia, NH3, to copper (II) ion, Cu^2+?

A

A light blue precipitate of copper (II) hydroxide, Cu(OH)2 is formed
Fe^3+ (aq) + 3OH^- (aq) –> Cu(OH)2 (s)

31
Q

What can you observe when you add in excess ammonia, NH3, to copper (II) ion, Cu^2+?

A

Light blue precipitate dissolves in excess to form a dark blue solution

32
Q
A

Pure Chemistry (Sec 3) (8 decks)

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