Topic 1 - Qualitative Analysis

Question 1

What is qualitative analysis?

Answer 1

• Tells you what is present

- Allows you to tell if a particular substance is present

Question 2

When might a qualitative analysis be used?

Answer 2

-To detect if there is a poisonous substance in drinking water

Question 3

What is quantitative analysis?

Answer 3

-Tells you how much is present

Question 4

When might quantitative analysis be used?

Answer 4

-Suspected drink-drivers to see how much alcohol in blood

Question 5

How do you test for positive ions using sodium hydroxide?

Answer 5

• Many metal hydroxides are insoluble, precipitate out of solution when formed. Some of these hydroxides have characteristic colours
• Add sodium hydroxide solution to solution of mystery compound
• Can use the colour of the insoluble hydroxide formed to see which metal was in the compound

Question 6

When the precipitate test is done, what colour precipitate does calcium [2+] form and what is the equation for this reaction?

Answer 6

White

Ca 2+ + 2OH - –> Ca(OH)2(s)

Question 7

When the precipitate test is done, what colour precipitate does copper (II) [2+] form and what is the equation for this reaction?

Answer 7

Blue

Cu 2+ + 2OH - –> Cu(OH)2(s)

Question 8

When the precipitate test is done, what colour precipitate does iron (II) [2+] form and what is the equation for this reaction?

Answer 8

Green

Fe 2+ + 2OH - –> Fe(OH)2(s)

Question 9

When the precipitate test is done, what colour precipitate does iron (III) [3+] form and what is the equation for this reaction?

Answer 9

Brown

Fe 3+ + 3OH - –> Fe(OH)3(s)

Question 10

When the precipitate test is done, what colour precipitate does aluminium [3+] form and what is the equation for this reaction?

Answer 10

White first - redissolves in excess NaOH forming a colourless solution
Al 3+ + 3OH - –> Al(OH)3(s) then
Al(OH)3 (s) + OH- –> Al(OH)4 -

Question 11

When the precipitate test is done, what colour precipitate does ammonium (NH4) [+] form?

Answer 11

No precipitate formed but heat given off as ammonia

Question 12

How can you identify ammonia gas?

Answer 12

-Turns Universal indicator paper purple
-Turns damp red litmus paper blue
(-Also has a distinct smell)

Question 13

How would you test for a halide using nitric acid and silver nitrate?

Answer 13

• Add dilute nitric acid HNO3 to the halide solution (forms a nitrate and hydrochloric acid)
• Add silver nitrate AgNO3 to form nitric acid, silver and a halogen
• The silver and the halogen react forming a precipitate

Question 14

When the test for halides is done, what colour precipitate does chlorine form and what is the equation for the final reaction in the test?

Answer 14

White

Ag+ + Cl- –> AgCl(s)

Question 15

When the test for halides is done, what colour precipitate does bromiene form and what is the equation for the final reaction in the test?

Answer 15

Cream

Ag+ + Br- –> AgBr(s)

Question 16

When the test for halides is done, what colour precipitate does iodine form and what is the equation for the final reaction in the test?

Answer 16

Yellow

Ag+ + I- –> AgI(s)

Question 17

What colour flame does sodium Na[+] form in the flame test?

Answer 17

yellow/orange

Question 18

What colour flame does potassium K[2+] form in the flame test?

Answer 18

lilac

Question 19

What colour flame does copper Cu [+] form in the flame test?

Answer 19

blue-green

Question 20

What colour flame does calcium Ca[2+] form in the flame test?

Answer 20

brick-red

Question 21

How do you test for carbonates?

Answer 21

• Add dilute acid which gives off CO2 if it is a carbonate

- CO2 turns limewater cloudy/milky

Question 22

How do you test for sulphates?

Answer 22

• Add hydrochloric acid and barium chloride

- Forms a white precipitate of barium sulphate