group 7

Question 1

What are the observations when NaF/ NaCl react with concentrated sulfuric acid

Answer 1

white steamy fumes

Question 2

What is the role of H2SO4 when NaF/NaCl react with H2SO4

Answer 2

Acid (proton donor)

Question 3

What are the observations when NaBr reacts with H2SO4

Answer 3

White steamy fumes when HBr evolve
Orange fumes of bromine
Colourless acidic gas

Question 4

What are the observations when NaI reacts with H2SO4

Answer 4

White steamy fumes when HI evolve
Black solid + purple fumes when Iodine evolves
colourless acidic gas SO2
Yellow solid of sulfur
H2S gas with bad egg smell

Question 5

What forms when silver nitrate reacts with Br-

Answer 5

AgBr

Ag2CO3

Question 6

What forms when excess nitric acid is added to AgBr and Ag2CO3, write the reactions

Answer 6

Br-
CO2

AgBr + 2NH3 –> [Ag(NH3)2]+ + Br-

Question 7

AgCl precipitate

Answer 7

white

Question 8

AgBr precipitate

Answer 8

cream

Question 9

AgI precipitate

Answer 9

pale yellow

Question 10

Silver chloride + dilute ammonia

Answer 10

Dissolves
AgCl + 2NH3 –> [Ag(NH3)s]+ + Cl-
Colourless solution

Question 11

Silver bromide + concentrated ammonia

Answer 11

Dissolves
AgBr + 2NH3 –> [Ag(NH3)2]+ + Br-
Colourless solution

Question 12

Silver iodide + ammonia

Answer 12

No reaction - too insoluble

Question 13

What does nitric acid do in group 7 reactions

Answer 13

React with carbonates to get rid of/ prevent formation of Ag2CO3

Question 14

Calcium hydroxide ppt colour

Answer 14

white

Question 15

Strontium hydroxide

Answer 15

does not form hydroxide precipitate due to high solubility

solution highly alkaline

Question 16

barium hydroxide

Answer 16

does not form hydroxide precipitate due to high solubility

highly alkaline

Question 17

Magnesium + sulfate

Answer 17

does not form sulfate precipitate due to high solubility

Question 18

Calcium + sulfate

Answer 18

does not form sulfate precipitate due to high solubility

Question 19

strontium + sulfate

Answer 19

white precipitate

Question 20

barium + sulfate

Answer 20

white precipitate

Question 21

Test for ammonium

Answer 21

Add NaOH and heat gently with litmus present

If NH4+ present, litmus will go red

Question 22

Give an equation between iodide ions and sulfuric acid to produce acidic colourless gas

Answer 22

2H+ + 2I- + H2SO4 –> I2 + SO2 + 2H2O

Question 23

Give an equation between iodide ions and sulfuric acid to produce yellow solid

Answer 23

6H+ + 6I- + H2SO4 –> 3I2 + S + 4H2O

Question 24

Give an equation between iodide ions and sulfuric acid to produce foul smelling gas

Answer 24

8H+ + 8I- + H2SO4 –> 4I2 + H2S + 4H2O

Question 25

Give an equation between bromide ions and sulfuric acid to produce acidic colourless gas

Answer 25

2H+ + 2Br- + H2SO4 --> Br2 + SO2 + 2H2O

Question 26

why is a excess of silver nitrate added

Answer 26

To make sure all halide ions are removed from solution

Question 27

A solution of sodium chlorate(l) was added to a colourless solution of potassium iodide. Suggest what is observed.

Answer 27

Chlorine oxidises iodine, so solution turns brown