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A Level Chemistry > Analysis of inorganic compounds > Flashcards

Analysis of inorganic compounds Flashcards

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1
Q

How is a flame test carried out?

A

Dip a nichrome wire or silica glass flame test rod into concentrated hydrochloric acid (to clean it) then into the sample. Place the rod into the hottest part of the bunsen flame and look for a colour. If no colour is obvious, repeat. Ignore any faint yellow/orange colours that will be due to sodium impurities

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2
Q

What colour flame does a lithium ion produce?

A

Carmine red (eye cannot distinguish between lithium and strontium)

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3
Q

What colour flame does a sodium ion produce?

A

Intense yellow

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4
Q

What colour flame does a potassium ion produce?

A

Lilac

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5
Q

What colour flame does a calcium ion produce?

A

Brick red

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6
Q

What colour flame does a strontium ion produce?

A

Crimson red (eye cannot distinguish between lithium and strontium)

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7
Q

What colour flame does a barium ion produce?

A

Green

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8
Q

What colour flame does a magnesium ion produce?

A

No colour

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9
Q

How is a sodium hydroxide test carried out?

A

Dissolve a small amount of the unknown compound in distilled water (if it is a solid), and if it does not dissolve completely then add dilute nitric acid (all metal nitrates are soluble). Add dilute aqueous sodium hydroxide until a precipitate forms. If dilute nitric acid has been added then lots of sodium hydroxide solution may need to be added to neutralise the acid before a precipitate appears

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10
Q

What is seen when sodium hydroxide is added to a compound containing magnesium ions?

A

White powdery precipitate of magnesium hydroxide

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11
Q

What is seen when sodium hydroxide is added to a compound containing calcium ions?

A

White powdery precipitate of calcium hydroxide

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12
Q

What is seen when sodium hydroxide is added to a compound containing strontium ions?

A

White powdery precipitate of strontium hydroxide

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13
Q

What is seen when sodium hydroxide is added to a compound containing lithium ions?

A

White powdery precipitate of lithium hydroxide. In the reaction, water is also formed, and the concentration of lithium ions must be high for a precipitate to form

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14
Q

What is seen when sodium hydroxide is added to a compound containing barium ions?

A

Very faint white precipitate, but almost none, of barium hydroxide

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15
Q

What is seen when sodium hydroxide is added to a compound containing sodium ions? CHECK

A

Clear, colourless solution. Precipitate formed is soluble

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16
Q

What is seen when sodium hydroxide is added to a compound containing potassium ions?

A

Clear, colourless solution. Precipitate formed is soluble

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17
Q

What is seen when sodium hydroxide is added to a compound containing ammonium ions?

A

Clear, colourless solution. Precipitate formed is soluble

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18
Q

What is seen when sodium sulphate solution or dilute sulphuric acid is added to a compound containing barium ions?

A

Immediate thick white precipitate of barium sulphate

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19
Q

What is seen when sodium sulphate solution or dilute sulphuric acid is added to a compound containing strontium ions?

A

White precipitate of strontium sulphate forms within 30 seconds

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20
Q

What is seen when sodium sulphate solution or dilute sulphuric acid is added to a compound containing calcium ions?

A

Normally no precipitate. but if the calcium ions are concentrated then there will be a white precipitate of calcium sulphate

21
Q

What is seen when sodium sulphate solution or dilute sulphuric acid is added to a compound containing magnesium ions?

A

No precipitate because magnesium sulphate is soluble

22
Q

How is the test for ammonium ions carried out?

A

When warmed with alkalis, ammonium compounds release ammonia gas. The test works best when a solid compound (rather than solution) is warmed with the alkali (usually sodium hydroxide is used), and ammonia is identified by its pungent smell, turning damp red litmus paper blue and creating a dense white smoke of ammonium chloride with the stopper of a bottle of concentrated hydrochloric acid (hydrogen chloride gas).
The reaction is warmed as ammonia gas is extremely soluble in water, and by heating it, the ammonia will bubble out of solution and can then be identified

23
Q

What is seen when sodium hydroxide is added to a compound containing ammonium ions and warmed?

A

Ammonia released - damp red litmus turns blue, white smoke formed with the stopper of a bottle of concentrated hydrochloric acid (NH4Cl)

24
Q

How is the test for carbonate ions carried out?

A

Add dilute aqueous hydrochloric or nitric acid to an unknown solid, and if there is effervescence then the gas is likely CO2, test with limewater. Presence of CO2 is evidence for a carbonate ion

25
Q

What is seen when hydrochloric acid is added to a compound containing carbonate or hydrogencarbonate ions?

A

Effervescence - CO2 released, gas turns limewater milky (either ion will react to produce CO2 and H2O)

26
Q

How is a test for halide ions using concentrated sulfuric acid carried out?

A

Add a little concentrated sulfuric acid to a small amount of the solid sample. Each halide ion gives a very different result

27
Q

What is seen when concentrated sulfuric acid is added to a compound containing chloride ions?

A

Vigorous effervescence, steamy fumes of HCl

28
Q

What is seen when concentrated sulfuric acid is added to a compound containing bromide ions?

A

Vigorous effervescence, steamy fumes of HBr, orange colour of Br2 (produced as HBr reacts with the H2SO4)

29
Q

What is seen when concentrated sulfuric acid is added to a compound containing iodide ions?

A

Vigorous effervescence, brown/black solid of iodine, purple vapour of iodine, yellow solid of sulfur, egg smell of hydrogen sulfide

30
Q

How is a test for halide ions using silver nitrate carried out?

A

Add silver nitrate and dilute nitric acid to an aqueous solution of the compound being tested, and a precipitate will form. As precipitate colours are hard to differentiate, additional tests can be carried out. With the addition of dilute aqueous ammonia solution or concentrated ammonia solution (ammonium hydroxide) some precipitates will dissolve

31
Q

What is seen when silver nitrate and nitric acid and then ammonia solution are added to a compound containing chloride ions?

A

White precipitate forms which dissolves easily in both dilute and concentrated ammonia solution to give a colourless solution

32
Q

What is seen when silver nitrate and nitric acid and then ammonia solution are added to a compound containing bromide ions?

A

Cream precipitate forms which dissolves with difficulty in dilute ammonia solution to give a colourless solution but is soluble in concentrated ammonia

33
Q

What is seen when silver nitrate and nitric acid and then ammonia solution are added to a compound containing iodide ions?

A

Primrose yellow precipitate forms which is insoluble in dilute and concentrated ammonia solution

34
Q

How is a chlorine water test carried out?

A

Chlorine water is used as an oxidising agent to confirm the presence of bromide or iodide. Adding an equal volume of chlorine water (sometimes with hydrochloric acid to ensure that chlorine is released from the bleach tablets used to make the water). Hexane or starch solution may be added to confirm the identity of the ions

35
Q

What is seen when chlorine water is added to a solution containing bromide ions?

A

Solution turns orange/yellow. If hexane is added to confirm the identity of the ions then the solution will be orange (Br2)

36
Q

What is seen when chlorine water is added to a solution containing iodide ions?

A

Solution turns reddy-brown. If starch solution is added then the solution turns blue black if iodide ions are present, and if hexane is added then it will turn pink/purple (I2)

37
Q

How is a barium chloride test carried out?

A

Used to identify sulfates (barium sulfate is insoluble in water). Add an aqueous solution of barium nitrate to an aqueous solution containing sulfate ions and a white precipitate forms. If acid is added before the barium chloride solution then no precipitate is given with a carbonate ion as it will have reacted with the acid, but if the barium chloride is added first then a precipitate will form with both anions

38
Q

What would be seen if barium chloride was added to a solution containing sulfate ions?

A

White precipitate of barium sulfate forms that does not dissolve in dilute acid

39
Q

What would be seen if barium chloride was added to a solution containing carbonate ions?

A

White precipitate of barium carbonate that dissolves in cold, dilute acid to give off CO2 gas

40
Q

How should a test where you heat a solid be carried out?

A

Ensure they are heated strongly with a Bunsen burner on a roaring flame to allow any decomposition to occur. Do not put your nose directly over a test tube to smell a gas. Look out for solids that melt on initial heating as they dissolve in their own water of crystallisation, and continue heating these solids until all the water of crystallisation has been driven off

41
Q

What is seen when a compound containing nitrate ions is heated?

A

Brown gas (NO2) is given off, gas relights a glowing splint (O2). If dilute HCl is added to the remaining solid (NO2^-) then there will be effervescence with the evolution of a brown gas and sometimes a blue solution to confirm the original solid was a nitrate

42
Q

What is seen when a compound containing carbonate ions is heated?

A

Colourless gas is given off which turns limewater milky.

43
Q

What is the solubility of nitrates and ethanoates?

A

All nitrates and common ethanoates are soluble in water

44
Q

What is the solubility of sodium, potassium and ammonium compounds?

A

All common sodium, potassium and ammonium compounds are soluble in water

45
Q

What is the solubility of chlorides?

A

All common chlorides are soluble in water except silver chloride and lead (II) chloride (but it is soluble in hot water)

46
Q

What is the solubility of sulfates?

A

All common sulfates are soluble in water except lead (II) sulfate, calcium sulfate, strontium sulfate and barium sulfate

47
Q

What is the solubility of carbonates?

A

All common carbonates are insoluble in water except sodium carbonate, potassium carbonate and ammonium carbonate

48
Q

What is the solubility of hydroxides?

A

All common hydroxides are insoluble in water except sodium hydroxide, potassium hydroxide and ammonium hydroxide. Lithium hydroxide, calcium hydroxide, strontium hydroxide and barium hydroxide are slightly soluble. Solubility of hydroxides increases down groups 1 and 2

A Level Chemistry (25 decks)

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