3.3.3 group 7 , the halogens Flashcards
explain the trend in the boiling points of the elements
- down the group boiling point increases
- number of electrons increases so strength of van der waals forces increases
- more energy needed to overcome these bonds
explain the trend in electronegativity of the elements
- down the group electronegativity decreases
- atomic radius increases due to more energy levels, shielding effect increases
- weaker attraction between nucleus and shared pair of electrons in a covalent bond
what is the trend in strength of oxidising agent?
- down the group elements decrease in oxidising strength
what makes something a good oxidising agent?
the better a species is at gaining electrons
outline what happens in a halogen displacement reaction
- they are redox reactions
- the halogen acts as an oxidising agent gaining electrons from the halide ion and becoming reduced
explain the trend in reducing ability of the halide ions?
- as you go down the group the reducing ability increases
- as you go down the group the ionic radius increases increasing the ability of the halide ion to lose an electron
how can the reducing abilities of the halides be compared?
- react with concentrated sulphuric acid
- takes part in 2 stages: an acid base displacement reaction and redox reaction
what sodium halides take part in the acid base displacement reaction?
all sodium halides
what sodium halides take part in the redox reaction?
NaBr and NaI
in the displacement reaction, what are the roles of the solid sodium halides and the sulphuric acid?
sodium halides: base (proton acceptor)
sulphuric acid: acid (proton donor)
why is it only NaBr and NaI that take part in the redox reaction?
- fluoride and chloride ions are not strong enough reducing agents to reduce sulphuric acid
what is a product of a redox reaction between sulphuric acid and bromide ions?
SO2 (choking gas)
what is the oxidation product from a redox reaction between sulphuric acid and iodide?
I2 - observed as a black solid / purple vapour
what is the reduction product observed in a redox reaction between sulphuric acid and iodide?
S - observed as a yellow solid
what is reduction product in a redox reaction between sulphuric acid and iodide?
H2S - observed as a gas with a bad egg smell
write a half equation to show the oxidation of bromide ions to bromine
2Br- — Br2 + 2e-
write a half equation for the reduction of sulphuric acid to sulphur dioxide
H2SO4 + 2H+ + 2e- — SO2 + 2H2O
write a half equation to show the oxidation of iodide ions to iodine
2I- — I2 + 2e-
write a half equation for the reduction of sulphuric acid to sulphur
H2 SO4 + 6H+ + 6e- — S + 4H2O
Write a half equation for the reduction of sulphuric acid to hydrogen sulphide
H2SO4 + 8H+ + 8e- — H2S + 4H2O
what products does iodide reduce to?
S
H2S
SO2
what products does bromide reduce to?
SO2 only
what can you use to identify and distinguish between halide ions?
acidified silver nitrate
explain how you would distinguish chloride ions
- acidify with nitric acid
- add silver nitrate
- add dilute then conc ammonia
- white precipitate forms that dissolves in NH3 forms
write out an ionic equation between chloride ions and silver ions
Cl- + Ag+ — AgCl
explain how you would distinguish bromide ions
- acidify with nitric acid
- add silver nitrate
- add dilute then concentrated ammonia
- cream precipitate forms that dissolves in concentrated ammonia
explain how you would distinguish iodide ions
- acidify with nitric acid
- add silver nitrate
- add dilute then concentrated ammonia
- yellow precipitate forms that doesn’t dissolve in either dilute or concentrated ammonia
explain how you would test for ammonium ions (method, observation and ionic equ)
- add NaOH and gently heat
- hold damp red litmus paper at the mouth of a boiling tube
- observation: fumes turn litmus paper from red to blue
- NH4+ (aq) + OH-(aq) — NH3(g) + H2O(l)
explain how you would test carbonate ions (method,observation and ionic equ)
- add dilute HCl
- colllect gas and bubble through limewater
- observation: fizzing, bubbling effervescence limewater turns cloudy due to white precipitate forming
- CO3 2- +2H+ — CO2 +H2O
explain how you would test for sulphate ions (method, observation and ionic equ)
- acidify with HCl
- add BaCl2
- observation: white precipitate forms
- Ba2+ + SO42- — BaSO4
write an equation to show what occurs when chlorine reacts with cold water
Cl2 + H2O — 2H+ + Cl- + ClO-
write an equation to show the reaction of chlorine and water in direct sunlight
2Cl2 +2H2O — 4HCl + O2
what is a benefit of using chlorine in water treatment?
- chlorine is toxic to bacteria which can cause disease so it protects health if population
what is a risk of using chlorine in water treatment?
- chlorine is also toxic to humans so there are risks associated with gas leaks during chlorination
- risk of formation of chlorinated hydrocarbons
write an equation to show the reaction between chlorine and cold aqueous sodium hydroxide
2NaOH + Cl2 — NaClO + NaCl + H2O
what is an observation for the displacement reaction for all sodium halides?
misty white fumes
what is an observation for the displacement reaction for all sodium halides?
misty white fumes
