group 7

Question 1

state the name of the reaction that has taken place when silver reacts with chloride ions in the halide test?

Answer 1

• precipitation reaction

Question 2

what is thermal decomposition?

Answer 2

• it is when a compound breaks down when heated

Question 3

which halogen is extremely toxic and vaporises readily at room temperature?

Answer 3

• bromine

Question 4

how does fluorine exist?

Answer 4

• a pale yellow gas

Question 5

how does chlorine exist?

Answer 5

• a pale green gas

Question 6

how does bromine exist?

Answer 6

• an orange brown liquid

Question 7

how does iodine exist?

Answer 7

• shiny grey black solid

Question 8

what colour are solutions of iodine and bromine in water and how do we tell them apart?

Answer 8

• they appear a similar orange-brown colour
• to tell the difference, we add the organic solvent cyclohexane and shake
• iodine will appear violet

Question 9

why can we tell iodine and bromine in water apart with cyclohexane better?

Answer 9

• cyclohexane is a non polar solvent and halogens are non polar too
• so they dissolve more readily and their colours are easier to tell apart

Question 10

why is astatine extremely rare?

Answer 10

• because it is radioactive and decays rapidly

- it is predicted to be the least reactive halogen

Question 11

what type of reaction takes place when chlorine is added to water and what is the equation?

Answer 11

• disproportionation where the dome element, in this case chlorine, is both oxidised and reduced
• Cl2 + H2O&raquo_space;» HClO + HCl

Question 12

why is chlorine added to water?

Answer 12

• chloric acid acts as a bleach
• chloric acid kills bacteria and microorganisms present in water
• reduces the incidence of water borne diseases

Question 13

how can we show that chloric acid is a bleach?

Answer 13

• with indicator solution
• first the solution appears red due to the presence of the two acids
• the it appears white as chloric acid starts to take action

Question 14

why is the reaction of chlorine with water limited and so what is the solution?

Answer 14

• low solubility of chlorine with water
• add chlorine to cold, dilute sodium hydroxide because if the water contains NaOH, much more chlorine dissolves and another disproportionation reaction can take place

Question 15

write the equation when chlorine reacts with cold, dilute sodium hydroxide

Answer 15

• Cl2 + NaOH&raquo_space;> NaCl + NaClO + H2O

Question 16

what is one use of sodium chlorate?

Answer 16

• household bleach

Question 17

what is the risk of using chlorine?

Answer 17

• chlorine is an extremely toxic gas
• in small concentrations, it is a respiratory irritant
• in large concentrations, it can be fatal

Question 18

what is another risk of adding chlorine to drinking water?

Answer 18

• chlorine can react with hydrocarbons like methane which is produced from decaying vegetation to produce chlorinated hydrocarbons
• chlorinated hydrocarbons are suspected of being carcinogenic

Question 19

why do we still add chlorine to water even if there are risks?

Answer 19

• the risk of not adding chlorine to the water supply is far greater than the risk posed by chlorinated hydrocarbons

Question 20

what is the reaction that happens during the test for halide ions called?

Answer 20

• precipitation reaction

Question 21

what do bromide ions reduce sulphuric acid into?

Answer 21

• SO2

Question 22

what do iodide ions reduce sulphuric acid into?

Answer 22

• H2S….. hydrogen sulfide