Chemical tests

Question 1

what is silver nitrate acidified with and why?

Answer 1

• nitric acid

- remove carbonate ions

Question 2

what colour is the precipitate for AgCl?

Answer 2

white

Question 3

what colour is the precipitate for AgBr?

Answer 3

cream

Question 4

what colour is the precipitate for AgI?

Answer 4

yellow

Question 5

why is ammonia used to double check halide precipitates?

Answer 5

can be hard to distinguish precipitates

- can test solubility in ammonia

Question 6

what is solubility of AgCl/AgBr/AgI?

Answer 6

AgCl= soluble in dilute ammonia
AgBr= soluble in conc ammonia
AgI = insoluble in conc ammonia

Question 7

how do you prepare the wire before flame test?

Answer 7

dip dichrome wire in HCl acid to clean wire and helps form volatile chloride
dip in salt sample
hold wire to edge of transparent flame

Question 8

what colours are observed for Group 1: Na, Li and K?

Answer 8

Na = orange
Li = red
K = lilac

Question 9

what colours are observed for Group 2: Ca, Sr and Ba?

Answer 9

Ca= brick red
Sr = crimson
Ba = pale green

Question 10

what is another test for barium?

Answer 10

add sulphuric acid - produce white precipitate of barium sulphate

Question 11

test for carbonate/ sulfate

Answer 11

• add HCl acid
• add barium chloride
• produce white precipitate
• if no fizz = sulfate
• if fizz = carbonate = test CO2 gas with limewater milky

Question 12

test for metal ions

Answer 12

add NaOH
- no precipiate - heat solution - test gas with damp red iitmus paper = turn blue - ammonia
- white precipitate: Mg 2+, Ca 2+, Al 3+
(use excess NaOH - Al 3+ redissolves precipitate)
- coloured precipitate - blue=Cu2+; green=Fe2+; brown=Fe3+

Question 13

test for acid

Answer 13

• add sodium hydrogen carbonate

- produces salt, water and CO2