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Flashcards in Analysis of inorganic compounds Deck (48)
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1

How is a flame test carried out?

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

2

What colour flame does a lithium ion produce?

Carmine red (eye cannot distinguish between lithium and strontium)

3

What colour flame does a sodium ion produce?

Intense yellow

4

What colour flame does a potassium ion produce?

Lilac

5

What colour flame does a calcium ion produce?

Brick red

6

What colour flame does a strontium ion produce?

Crimson red (eye cannot distinguish between lithium and strontium)

7

What colour flame does a barium ion produce?

Green

8

What colour flame does a magnesium ion produce?

No colour

9

How is a sodium hydroxide test carried out?

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

10

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

White powdery precipitate of magnesium hydroxide

11

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

White powdery precipitate of calcium hydroxide

12

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

White powdery precipitate of strontium hydroxide

13

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

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

14

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

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

15

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

Clear, colourless solution. Precipitate formed is soluble

16

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

Clear, colourless solution. Precipitate formed is soluble

17

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

Clear, colourless solution. Precipitate formed is soluble

18

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

Immediate thick white precipitate of barium sulphate

19

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

White precipitate of strontium sulphate forms within 30 seconds

20

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

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

21

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

No precipitate because magnesium sulphate is soluble

22

How is the test for ammonium ions carried out?

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

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

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

24

How is the test for carbonate ions carried out?

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

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

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

26

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

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

27

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

Vigorous effervescence, steamy fumes of HCl

28

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

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

29

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

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

30

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

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