Identifying compounds

Question 1

What is the test for carbonates and hydrocarbonates?

Answer 1

Add acid to the carbonate (HCl)
Connect to test tube with limewater
If present the CO2 produced will turn limewater cloudy

Question 2

What is the result of the flame-test of Sodium?

Answer 2

Yellow-orange flame

Question 3

What is the result of the flame-test of Potassium?

Answer 3

Lilac flame

Question 4

What is the result of the flame-test of Calcium?

Answer 4

Brick red flame

Question 5

What is the result of the flame-test of Lithium?

Answer 5

Crimson red flame

Question 6

What is the result of the flame-test of Rubidium?

Answer 6

Reddish-violet

Question 7

What is the result of the flame-test of Caesium?

Answer 7

Blue-violet

Question 8

What is the result of the flame-test of Strontium?

Answer 8

Red

Question 9

What is the result of the flame-test of Barium?

Answer 9

Pale green

Question 10

What is the result of the flame-test of Copper?

Answer 10

Blue-green

Question 11

How do you perform a flame test?

Answer 11

Clean a nichrome wire in conc hydrochloric acid and put into Bunsen flame
Dip into small amount of solid and put into the Bunsen flame

Question 12

How is the test for halide ions done?

Answer 12

Dissolve solid in pure water
Acidified using dilute nitric acid
Silver nitrate (aqueous) added

Question 13

Why is dilute nitric acid when testing for halide ions?

Answer 13

Reacts with and removes other ions which may give a precipitate with silver nitrate

Question 14

What coloured precipitate forms if F- ions are present in a compound?

Answer 14

No precipitate

Question 15

What coloured precipitate forms if Cl- ions are present in a compound?

Answer 15

White precipitate

Question 16

What coloured precipitate forms if Br- ions are present in a compound?

Answer 16

Cream precipitate

Question 17

What coloured precipitate forms if I- ions are present in a compound?

Answer 17

Yellow precipitate

Question 18

How does AgCl react with ammonia solution?

Answer 18

Dissolves in dilute ammonia solution

Question 19

How does AgBr react with ammonia solution?

Answer 19

Precipitate doesn’t dissolve in dilute ammonia solution

Precipitate dissolves in conc ammonia solution giving colourless solution

Question 20

How does AgI react with ammonia solution?

Answer 20

Precipitate is insoluble in all concentrations of ammonia

Question 21

Which colour is fluorine?

Answer 21

Pale yellow

Question 22

Which colour is chlorine gas?

Answer 22

Green

Question 23

Which colour is bromine liquid?

Answer 23

Red-brown

Question 24

Which colour is iodine solid?

Answer 24

Grey solid

Question 25

What colour is chlorine in water and hexane?

Answer 25

Water: Virtually colourless Hexane: Virtually colourless

Question 26

What colour is bromine in water and hexane?

Answer 26

Water: Yellow/orange Hexane: Orange/red

Question 27

What colour is iodine in water and hexane?

Answer 27

Water: Brown Hexane: Pink/violet

Question 28

How do you test for sulphate ions?

Answer 28

Add dilute HCl Add Barium chloride solution Positive result gives a white precipitate

Question 29

Why is hydrochloric acid added in the test for sulphate ions?

Answer 29

Removes any traces of carbonate ions before the test

Question 30

What is the test for ammonium compounds?

Answer 30

Add some NaOH Gently heat Put damp litmus paper over test tube Positive test turns red litmus paper blue

Question 31

Where should the test for ammonia compounds be done?

Answer 31

Fume cupboard as produces an irritant gas

Question 32

Why does the litmus paper have to be damp when testing for ammonia ions?

Answer 32

Ammonia gas can dissolve and make the colour change

Question 33

What is the test for metal ions with NaOH?

Answer 33

Add sodium hydroxide to the metal ion solution

Question 34

What is the result for copper (II) sulphate when NaOH added?

Answer 34

Light blue precipitate forms

Question 35

What is the result for iron (II) when NaOH added?

Answer 35

Green precipitate | Darkens on standing as it forms iron (III) hydroxide

Question 36

What is the result for iron (III) when NaOH added?

Answer 36

Orange precipitate | Darkens on standing

Question 37

What is the result when cobalt (II) when NaOH is added?

Answer 37

Blue precipitate | Turns brown on standing

Question 38

What is the colour of copper(II) solution?

Answer 38

Pale blue solution

Question 39

What is the colour of iron(II) solution?

Answer 39

Pale green solution

Question 40

Why does iron(II) precipitate darken on standing?

Answer 40

``` Oxidised by water and oxygen in air Forms iron(II) hydroxide ```

Question 41

What is the colour of iron(III) solution?

Answer 41

Yellow solution

Question 42

What is the colour of cobalt(II) solution?

Answer 42

Pale pink solution

Question 43

What is the colour of cobalt nitrate?

Answer 43

Yellow-brown solution

Question 44

What is the colour of Chromium nitrate?

Answer 44

Purple

Question 45

What is the colour of Copper chloride?

Answer 45

Yellow solution

Question 46

What is the colour of cobalt chloride?

Answer 46

Blue

Question 47

How do you test for SO2?

Answer 47

Turns potassium dichromate paper orange to green

Question 48

How do you test for H2S?

Answer 48

Turns lead ethanoate paper from white to black

Question 49

How could you tell the difference between an aldehyde and ketone using 2,4-DNP?

Answer 49

``` React both with 2,4-DNP Take yellow precipitate and recrystallise Make crystal dry Determine melting point Compare to data booklet value ```