group 7 Flashcards
state the name of the reaction that has taken place when silver reacts with chloride ions in the halide test?
- precipitation reaction
what is thermal decomposition?
- it is when a compound breaks down when heated
which halogen is extremely toxic and vaporises readily at room temperature?
- bromine
how does fluorine exist?
- a pale yellow gas
how does chlorine exist?
- a pale green gas
how does bromine exist?
- an orange brown liquid
how does iodine exist?
- shiny grey black solid
what colour are solutions of iodine and bromine in water and how do we tell them apart?
- they appear a similar orange-brown colour
- to tell the difference, we add the organic solvent cyclohexane and shake
- iodine will appear violet
why can we tell iodine and bromine in water apart with cyclohexane better?
- 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
why is astatine extremely rare?
- because it is radioactive and decays rapidly
- it is predicted to be the least reactive halogen
what type of reaction takes place when chlorine is added to water and what is the equation?
- disproportionation where the dome element, in this case chlorine, is both oxidised and reduced
- Cl2 + H2O»_space;» HClO + HCl
why is chlorine added to water?
- chloric acid acts as a bleach
- chloric acid kills bacteria and microorganisms present in water
- reduces the incidence of water borne diseases
how can we show that chloric acid is a bleach?
- 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
why is the reaction of chlorine with water limited and so what is the solution?
- 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
write the equation when chlorine reacts with cold, dilute sodium hydroxide
- Cl2 + NaOH»_space;> NaCl + NaClO + H2O
what is one use of sodium chlorate?
- household bleach
what is the risk of using chlorine?
- chlorine is an extremely toxic gas
- in small concentrations, it is a respiratory irritant
- in large concentrations, it can be fatal
what is another risk of adding chlorine to drinking water?
- chlorine can react with hydrocarbons like methane which is produced from decaying vegetation to produce chlorinated hydrocarbons
- chlorinated hydrocarbons are suspected of being carcinogenic
why do we still add chlorine to water even if there are risks?
- the risk of not adding chlorine to the water supply is far greater than the risk posed by chlorinated hydrocarbons
what is the reaction that happens during the test for halide ions called?
- precipitation reaction
what do bromide ions reduce sulphuric acid into?
- SO2
what do iodide ions reduce sulphuric acid into?
- H2S….. hydrogen sulfide
