Chapter 8 reactivity trends Flashcards
Describe the redox reactions of group 2 elements
- group 2 elements has two electrons in its outer shell
- each metal atom is oxidised to a 2+ ion with electron configuration of a obel gas
- another species will gain 2 electrons and be reduced
- group 2 element is the reducing agent as reduces another species
Describe redox reactions between group 2 elements and oxygen
- form a metal oxide - MO
- M2+ and O2- ions
- group 2 metal oxidation number increases - oxidation
- oxygen oxidation number decreases -reduced
Describe redo reactions between group 2 elements and water
- react with water to form alkaline hydroxide
- M(OH)2
- more reactive down group
- H in H2O is reduced
- and metal is oxidised
Describe the trend of reactivity and ionisation energy in group 2
- when redox reactions occur reactivity increases down group 2
- ionisation energies decrease down group because attraction between nucleus and outer electrons decreases increase atomic radius annd increase in shielding
- element become more reactive and stronger reducing agents down the group
Describe the reaction between group 2 oxides and water
- releasing Oh - ions when they react forming alkaline solutions of metal hydroxides
- metal hydroxides only slighty soluble in water
Describe the trend of solubility of hydroxides
- solubility increases down the group solutions containing more OH- ions and are more alkaline
Describe the use of group 2 compounds in agriculture
- calcium hydroxide is added to fiels as lime to increase pH of acidic soild
- neutralises acid forming nuetral water
Describe the use of group 2 compound in medicine
- used as antacids to treat acid indigestion
- magnesium and calcium carbonates
- milk of magnesia suspension of white magnesium hydroxide
- neutralises the acid in the stomach
Describe the trend of boiling points down group 7
- room temperature and pressure halogens exist aas diatomic molecules
- more electrons
- stronger london forces
- more enrgy required to break intemolecular forces
- boiling point increases
What state and colour is fluorine
- pale yellow
- gas
What state and colour is chlorine
- pale green
- gas
What state and colour is bromine
- red brown
- liquid
What state and colour is iodine
- shiny grey black
- solid
What state and colour is astatine
never been seen
Describe the redox reactions of halogens
- each halogen atoms is reduced gaining an electron to form 1- ion
- oxidising agent - oxidised another species
What do halogen halide displacement reactions show
- reactivity of halogens decreases down the group
What are halogen - halide displacement reactions
- a solution of each halogen is added to aqueous solution of other halides
- reaction takes place the halogen displacing the halide from the solution
- the solution changes colour
Describe the colour of Cl2 in water and cyclohexane
- pale green - water
- pale green - top layer - cyclohexane
Describe the colour of Br2 in water and cyclohexane
- orange - water
- orange - top layer - cyclohexane
Describe the colour of l2 in water and cyclohexane
- brown - water
- violet - top layer - cyclohexane
Describe the results of the halogen - halide displacement reactions
- Cl2 reacted with both Br- and I-
- orange solution formed with Br2 formation
- violet solution formed with I2 formation
- bromine reacted with I- only
- violet solution form I2 formation
- iodine not reacted at all
What is astatine
- extremely rare because it is radioacive and decause rapidly
- least reactive halogen
- never been seen
What is the trend of reactivity down group 7
- halogrns react by gaining electrons and tendency to gain an electron decreases becoming less reactive
- atomic radius increases
- shielding increases
- less nuclear attraction to capture an electron from another speices
- reactivity decreases
What is a disproportionation reaction
- redox reaction same element is both oxidised and reduced
Describe the reaction between chlorine and water and describe it benefit for the economy
- used for water purification - killing harmful bacteria
- Cl2(aq) + H2O (l) - > HClO(aq) + HCl(aq)
- dispropotionation reaction occurs
- bacteria killer by chloric(i) acid and chlorate ions ClO-
Describe the reaction of chlorine with cold dilute aquous sodium hydroxide
- Cl2(aq)+2NaOH(aq) -> NaClO(aq) +NaCl (aq) +H2O (l)
- resilting solution contains a large concentration of Chlorate (I) ions from sodium chlroate (I) NaClO is fformed
- used as household bleach
What are the benefits and risks of using chlorine
- make sure water is good to drink - chlorine is completley toxic gas and large concentrations can be fatal
- chlorine in drinking water can react with organic hydrocarbon formed from decaying vegitation chlroinated hydrocarbons are formed suspects of causing cancers
Describe the carbonate test
- react with acids to form carbon dioxide gas
- dilute nitric acid / hydrochloric acid
- bubble gas through limewater if it goes cloudy carbonate ions are present
Describe the sulfate test
- barium sulfate is in soluble so the white precipitate is the basis
- barium chlride or barium nitrate added to solution white precipitate of barium sulfate should form if sulfate ions are present
- Ba^2++So4^2- (aq) ->BaSO4 (s)
Describe the test and result for halide ions
- add aqueous silver nitrate AgNo3 to aquous solution of halide
- silver halide precipitates are different colours
- chloride - white - soluble in dilute NH3
- bromine - cream - soluble in conc NH3
- iodine - yellow - insoluble in conc NH3
- aquous ammonia to test the solubilityh of the precipitate to tell them apart
Describe the sequence of tests used for qualitative analysis and why
- carbonate test - add dilute acid - look for effervescence of carbon dioxide gas
- meither sulfate nor halide produced bubbles with dilute acid
- sulfate - barium chloride / barium nitried looking for white precipitate of barium sulfate
- barium carbonate insoluble in water so make sure no carbonate is present by doing the carbonate test first
- halide - add silver nitrate
- silver carbonate and sulfate are insoluble in water
How do you test for a mixture of ions
- carbonate test - keep addiding dilute nitric acid if see bubbles to remove all carbonate ions
- sulfate test - solution after carbonate aff excess of barium nitrate
- filter solution remove barium sulfate
- halide - solution left from sulfate add silver nitrate
- add Nh3 to confirm halide that you have
How do you test for ammonium ions
- NH4+(aq) + OH-(aq) -> Nh3(g) + H2O (l)
- aqueous sodium hydroxide NaOH is added to a solution of ammonium ions
- ammonia gas is produced - very soluble in water
- mixture warmed and ammonia gas is released
- ammonia is alkaline turn indicator paper blue
