Unit 7 - Analysis

Question 1

Test for ammonia

Answer 1

• it has a pungent smell
• turns damp red litmus paper blue
• with the stopper of concentrated HCl it gives a white smoke (ammonium chloride)

Question 2

Test for Cu++ (copper)

Answer 2

Dissolve compound in water and add dilute sodium hydroxide.
If test is positive, a pale blue precipitate will be formed.
Cu++ + 2OH- –> Cu(OH)2

Question 3

Test for Fe++ (iron II) ions

Answer 3

Dissolve compound in water and add dilute sodium hydroxide.
If test is positive, a moss green precipitate will be formed.
Fe++ + 2OH- –> Fe(OH)2

Question 4

What happens when you dissolve potassium, sodium, or ammonium ions in sodium hydroxide

Answer 4

There is no precipitate as these hydroxides are soluble in water

Question 5

Test for Cl- (chloride) ions

Answer 5

Dissolve the compound in water. Add aqueous silver nitrate and dilute aqueous nitric acid. If test is positive a white precipitate will form.
Ag+ + Cl- –> AgCl

Question 6

How to perform a flame test

Answer 6

Use a clean platinum wire
Dip it in concentrated hydrochloric acid
Dip it in powdered compound
View the colour of the flame

Question 7

Ion gives a brick red flame in a flame test

Answer 7

Ca++ (calcium)

Question 8

What colour gives an intense yellow flame in a flame test

Answer 8

Na+ (sodium)

Question 9

What ion gives a green (blue centre) flame in a flame test

Answer 9

Cu++ (copper)

Question 10

What ion gives a lilac flame in a flame test

Answer 10

K+ (potassium)

Question 11

What ion gives a bright red flame in a flame test

Answer 11

Li+ (lithium)

Question 12

Test for ion Br- (bromide)

Answer 12

Dissolve the compound in water. Add aqueous silver nitrate and dilute aqueous nitric acid. If test is positive a cream precipitate will form (silver bromide)

Question 13

Test for I- (iodide) ions

Answer 13

Dissolve the compound in water. Add aqueous silver nitrate and dilute aqueous nitric acid. If test is positive a primrose yellow precipitate will be formed (silver iodide)

Question 14

Test for the anion SO4 – (sulfate)

Answer 14

Dissolve the compound in water and add aqueous barium chloride solution (and HCl to remove carbonates). BaSO4 is insoluble in water so a white precipitate will form.

Question 15

Test for anion CO3 – (carbonate)

Answer 15

Add dilute HCl. If there is effervescence it is either CO2 or H2. If the gas is CO2 then a carbonate is present
CO3 – + 2H+ –> CO2 + H2O

Question 16

Test for hydrogen

Answer 16

Lit splint in gas gives a squeaky pop

Question 17

Hazards of hydrogen

Answer 17

It’s highly flammable (could explode)

Question 18

Test for oxygen

Answer 18

Glowing splint relights in gas

Question 19

Hazards of ammonia

Answer 19

It’s poisonous

Question 20

Test for carbon dioxide

Answer 20

Bubble gas through limewater, it goes milky (goes clear again after a while)

Question 21

Test for chlorine gas

Answer 21

Damp litmus paper is bleached white

Question 22

Hazards of chlorine

Answer 22

It’s highly poisonous

Question 23

Test for water vapour

Answer 23

Anhydrous copper sulfate turns from white to blue

Question 24

Test for NH4+ (ammonium)

Answer 24

Dissolve the compound in an alkali (sodium hydroxide) and heat it. On heating, ammonia is less soluble, so it is released.
NH4+ (s) + OH- (aq) –> NH3 (g) + H2O (g)