tests for group 7

Question 1

flame test for group 2 ions

Answer 1

1) dip nichorome wire into conc HCl
2) dip into sample
3) place the loop into the blue bunsen flame and observe the colour

Colours:
Ca - dark red
Sr -** red**
Ba - green

Question 2

test for ammonium compounds

Answer 2

1) add NaOH and gently heat
2) pt = ammonia gas produced
3) use damp litmus paper (paper turns blue)

Question 3

test for hydroxides (litmus paper)

Answer 3

pt = red litmus paper turns blue

Question 4

test for carbonates

Answer 4

bubble carbon dioxide through limewater (turns cloudy)

Question 5

test for sulfates

Answer 5

1) add HCl to remove any carbonates
2) add barium chloride (pt = white precipitate of barium sulfate)

Question 6

test for halides

Answer 6

1) dissolve solution in nitric acid then add silver nitrate dropwise
2) Silver chloride = white precipitate
Silver bromide = cream precipitate
Silver iodide = yellow precipitate

Question 7

follow up test for halides

Answer 7

1) add dilute followed by concentrated ammonia to the silver halide solution

• If precipitate dissolves in dilute ammonia = chloride ions present
• If the precipitate doesn’t dissolve in dilute, but does dissolve conc ammonia = bromide ions present
• If the precipitate doesn’t dissolve in dilute or concentrated ammonia = iodide ions present

Question 8

Reaction of bromide ions with H2SO4 (start with 2 NaBr + 2 H2SO4..)

Answer 8

PT - reddish-brown gas
(equation - 2 NaBr + 2 H2SO4 → Na2SO4 + SO2 + Br2 + 2 H2O)

Question 9

Reaction of iodide ions with H2SO4 (black)

Answer 9

PT -Black solid and yellow solid of sulfur H2S (Hydrogen sulfide), a gas with a bad egg smell

Question 10

reaction of chloride ions with H2SO4

Answer 10

PT - white fumes of HCl gas
equation - NaCl(s) + H2SO4 (l)&raquo_space;> NaHSO4 (s) + HCl(g)