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CSEC CHEMISTRY > C10: Identification of cations, anions and gases > Flashcards

C10: Identification of cations, anions and gases Flashcards

1
Q

what are the 3 main reagents used when performing tests to identify cations?

A
  • NaOH(aq)
  • Aqueous ammonia - NH4OH(aq)
  • potassium iodide(KI)
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2
Q

KI(aq) is used to distinguish between these 2 cations:

A

Pb2+

Al3+

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3
Q

what are the ions present?

A

A - Al3+

B - Pb2+

C - Zn2+

D - Ca2+

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4
Q

what are the ions present?

A

A - Cu2+

B - Fe2+

C - Fe3+

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5
Q

when drops of NaOH are added to a clear solution and a white precipitate is formed, the possible cations are (1)___________, (2)_____________, (3) _____________, (4)_____________.

A
  1. Al3+
  2. Pb2+
  3. Zn2+
  4. Ca2+
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6
Q

If excess NaOH(aq) is added to a white preciptitate and it dissolves, the possible cations are:

A

Al3+

Pb2+

Zn2+

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7
Q

If excess NH4+(aq) is added to a white preciptitate and it dissolves, the possible cations are:

A

Zn2+

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8
Q

when drops of NaOH are added to a clear solution and a white precipitate is formed, the possible cations are (1)___________, (2)_____________, (3) _____________, (4)_____________. If the solution remains clear then the cation present is (5)__________

A
  1. Al3+
  2. Pb2+
  3. Zn2+
  4. Ca2+
  5. NH4+
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9
Q

which of the following cations does NOT form a precipitate when drops of NaOH(aq) are added to its solution

Al3+

Pb2+

Zn2+

Ca2+

NH4+

Fe2+

Fe3+

Cu2+

A

NH4+

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10
Q

Precipitates of which of the following cations dissolve in excess NaOH(aq) and why

Al3+

Pb2+

Zn2+

Ca2+

NH4+

Fe2+

Fe3+

Cu2+

A

Al3+, Zn2+, Pb2+,

because they form amphoteric hydroxides which will react with aqueous NaOH(a strong base)

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11
Q

Zn2+ , Pb2+, and Al3+ will form white (1)_________when drops of NaOH are added to their solution because they form hydroxides which are (2)_________, however these salts are (3)_________oxides, so they will react with excess NaOH and dissolve

A
  1. precipitates
  2. insoluble
  3. amphoteric
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12
Q

the metal cations, except (1)___________ form (2)_____________ metal hydroxides with ammonium hydroxide solution(aqueous ammonia)

A
  1. Ca2+
  2. insoluble
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13
Q

when drops of NH4+ are added to a clear solution and a white precipitate is formed, the possible cations are (1)___________, (2)_____________, (3) _____________.

A
  1. Al3+
  2. Pb2+
  3. Zn2+
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14
Q

How to distinguish between Al3+ and Pb2+ ions

A

add a few drops of KI(aq) to solutions of their salts. A bright yellow precipitate of PbCl2 will form. Al3+ will form a soluble salt.

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15
Q

anions are identified by observing the effects of these on their salts:

A
  • heat,
  • dilute acid,
  • aqueous silver nitrate, and
  • barium chloride solution(or barium sulphate
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16
Q

what are the possible anions present in each case below?

A

A - Carbonate, nitrate

B - Carbonate, sulphate,

C- Chloride, bromide, iodide

D- carbonate, sulphate, sulphite

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17
Q

when a solid is heated a gas is obtained. what are the likely gasses?

A

CO2

NO2

O2

18
Q

what anion will give carbon dioxide when heated?

A

Carbonate ion

19
Q

what anions gives off O2 when heated?

A

nitrates of sodium and potassium

20
Q

what nitrates release nitrogen dioxide when heated?

A

nitrates of calcium and below

21
Q

If no gas is released on heating a salt what does this signify?

A

that the salt is unlikely a carbonate or nitrate i.e. does not contain carbonate or nitrate ions.

22
Q

dilute HCl or HNO3 is added to a small quantity of an unknown salt in a test tube and a gas evolves. The gas could either be(1)________ or( 2)_________.

A
  1. carbon dioxide
  2. sulphur dioxide
23
Q

if nothing happens when dilute acid is added to a salt what does this imply:

A

that the salt is not a carbonate or sulphite but may be a sulphate, nitrate or halide.

24
Q

when a few drops of conc. sulphuric acid are added to a small quantity of solid in a dry test tube a gas is produced. The gas could be:

A

carbon dioxide

sulphur dioxide

hydrogen chloride

bromine

iodine

25
Q

when a few drops of conc. sulphuric acid are added to a small quantity of solid in a dry test tube a red-brown gas is evolved. The gas could be:

26
Q

when a few drops of conc. sulphuric acid are added to a small quantity of solid in a dry test tube a grey-black solid is produced. The solid is most likely:

27
Q

a few drops of silver nitrate are added to a solution and precipitate is obtained. what anions are likley to be present based on the colour of the precipitate?

A
  • white precipitate - chloride(silver chloride)
  • cream precipitate - bromide(silver bromide)
  • pale yellow precipitate - iodide( silver iodide)
28
Q

A few drops of silver nitrate were added to three test tubes containing an unknown anion. The results are shown below. What is the possible anion present in each?

A

A - chloride

B - bromide

C - iodide

29
Q

sometimes the precipitates of AgCl, AgBr and AgI are difficult to tell apart especially in inadequate lighting. How can they be distinguished?

A

adding aqueous ammonia (NH4OH(aq)) to the precipitate:

  • AgCl - soluble
  • AgBr - partially soluble
  • AgI - insoluble, precipitate remains
30
Q

Three test tubes contain aqueous solutions of a carbonate, sulphite and sulphate respectively. How do we identify which is which?

A
  1. add a few drops of aqueous barium nitrate to each. a white precipitate will form in all three
  2. next add dilute HCl to each precipitate:
  • test tube where precipitate remains - sulphate ion present
  • test tube in which precipitate dissolves and releases a pungent odourless gas on heating - that reduces H+/KMNO4 and H+/K2CrO7 - sulphite ion present
  • test tube where precipitate dissolves and releases a colourless odorless gas that form a white precipitate with lime water - carbonate ion
31
Q

Identify the gas released in each test tube

A

A - chlorine

B - hydrogen chloride

C - sulphur dioxide

D - nitrogen dioxide

32
Q

Identify the gas released in each test tube

A

A - oxygen

B - hydrogen

C - carbon dioxide

D - ammonia gas

33
Q

flow chart summarizing identification of anions

34
Q

what do we need to remember when testing for anions?

A

anions are tested by looking at the effects of heat, dilute acid, aqueous silver nitrate, and barium chloride solution

35
Q

complete the following flow chart

A

A - heat

B - dilute acid

C - silver nitrate solution

D - barium chloride or barium nitrate solution

36
Q

how identify sulphate ions

A

Add HCl and Barium Chloride, white precipitate proves positive sulphate.

37
Q

how identify Chloride ions

A

HNO3 + AgNO3, white precipitate

38
Q

how identify bromide ions

A

HNO3 + AgNO3, cream precipitate

39
Q

how identify Iodide ions

A

HNO3 + AgNO3, yellow precipitate

40
Q

how identify Carbonates

A

Add HCl should make CO2

41
Q

How to identify nitrates

A

Apply heat:

  • oxygen produced for nitrates of potassium and sodium
  • nitrogen dioxide produced for nitrates of calcium or below

CSEC CHEMISTRY (17 decks)

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