T6 - Testing for Anions and Cations

Question 1

What is a flame test used for

Answer 1

To show the presence of certain metal ions in a compound

Question 2

How to carry out a flame test

Answer 2

• dip a platinum or nichrome wire into concentrated hydrochloric acid to remove any impurities
• dip the wire into the salt being tested
• hold the wire with the salt over a roaring bunsen burner flame
• observe the colour

Question 3

what colour is formed in the flame test for lithium

Answer 3

red

Question 4

what colour is formed in the flame test for sodium

Answer 4

yellow

Question 5

what colour is formed in the flame test for potassium

Answer 5

lilac

Question 6

what colour is formed in the flame test for calcium

Answer 6

orange-red

Question 7

what colour is formed in the flame test for copper II

Answer 7

blue-green

Question 8

what is the test for NH4+

Answer 8

• add sodium hydroxide and warm
• if ammonium ions are present then ammonia gas will form
• the ammonia gas will turn damp red litmus paper blue

Question 9

what is the test for Cu2+, Fe2+ and Fe3+

Answer 9

add sodium hydroxide and observe the colour

Question 10

What will form if Copper (II) ions are present, using sodium chloride

Answer 10

a blue precipitate

Question 11

What will form if Iron (II) ions are present, using sodium chloride

Answer 11

a green precipitate

Question 12

What will form if Iron (III) ions are present, using sodium chloride

Answer 12

brown/red precipitate

Question 13

What is the test for Cl-, Br- and I- (Halide ions)

Answer 13

• Add nitric acid to remove impurities
• add silver nitrate solution and observe

Question 14

What will happen to chloride ions if they are present, using silver nitrate solution

Answer 14

a white precipitate will form

Question 15

What will happen to bromide ions if they are present, using silver nitrate solution

Answer 15

a cream precipitate will form

Question 16

What will happen to iodide ions if they are present, using silver nitrate solution

Answer 16

a yellow precipitate will form

Question 17

How do you test for sulfate ions

Answer 17

• Add HCl to remove impurities
• Add Barium chloride solution and observe

Question 18

what will happen if sulfate ions are present, using barium chloride solution

Answer 18

a white precipitate will form

Question 19

How do you test for carbonate ions

Answer 19

• add HCl and observe

Question 20

What will happen if carbonate ions are present, using HCl

Answer 20

effervescence

Question 21

How can you identify the gas formed using HCl

Answer 21

test for carbon dioxide using limewater - if carbon dioxide is present, the limewater will turn cloudy