Chapter 8 reactivity trends

Question 1

Describe the redox reactions of group 2 elements

Answer 1

• 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

Question 2

Describe redox reactions between group 2 elements and oxygen

Answer 2

• form a metal oxide - MO
• M2+ and O2- ions
• group 2 metal oxidation number increases - oxidation
• oxygen oxidation number decreases -reduced

Question 3

Describe redo reactions between group 2 elements and water

Answer 3

• react with water to form alkaline hydroxide
• M(OH)2
• more reactive down group
• H in H2O is reduced
• and metal is oxidised

Question 4

Describe the trend of reactivity and ionisation energy in group 2

Answer 4

• 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

Question 5

Describe the reaction between group 2 oxides and water

Answer 5

• releasing Oh - ions when they react forming alkaline solutions of metal hydroxides
• metal hydroxides only slighty soluble in water

Question 6

Describe the trend of solubility of hydroxides

Answer 6

• solubility increases down the group solutions containing more OH- ions and are more alkaline

Question 7

Describe the use of group 2 compounds in agriculture

Answer 7

• calcium hydroxide is added to fiels as lime to increase pH of acidic soild
• neutralises acid forming nuetral water

Question 8

Describe the use of group 2 compound in medicine

Answer 8

• 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

Question 9

Describe the trend of boiling points down group 7

Answer 9

• room temperature and pressure halogens exist aas diatomic molecules
• more electrons
• stronger london forces
• more enrgy required to break intemolecular forces
• boiling point increases

Question 10

What state and colour is fluorine

Answer 10

• pale yellow
• gas

Question 11

What state and colour is chlorine

Answer 11

• pale green
• gas

Question 12

What state and colour is bromine

Answer 12

• red brown
• liquid

Question 13

What state and colour is iodine

Answer 13

• shiny grey black
• solid

Question 14

What state and colour is astatine

Answer 14

never been seen

Question 15

Describe the redox reactions of halogens

Answer 15

• each halogen atoms is reduced gaining an electron to form 1- ion
• oxidising agent - oxidised another species

Question 16

What do halogen halide displacement reactions show

Answer 16

• reactivity of halogens decreases down the group

Question 17

What are halogen - halide displacement reactions

Answer 17

• 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

Question 18

Describe the colour of Cl2 in water and cyclohexane

Answer 18

• pale green - water
• pale green - top layer - cyclohexane

Question 19

Describe the colour of Br2 in water and cyclohexane

Answer 19

• orange - water
• orange - top layer - cyclohexane

Question 20

Describe the colour of l2 in water and cyclohexane

Answer 20

• brown - water
• violet - top layer - cyclohexane

Question 21

Describe the results of the halogen - halide displacement reactions

Answer 21

• 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

Question 22

What is astatine

Answer 22

• extremely rare because it is radioacive and decause rapidly
• least reactive halogen
• never been seen

Question 23

What is the trend of reactivity down group 7

Answer 23

• 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

Question 24

What is a disproportionation reaction

Answer 24

• redox reaction same element is both oxidised and reduced

Question 25

Describe the reaction between chlorine and water and describe it benefit for the economy

Answer 25

• 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-

Question 26

Describe the reaction of chlorine with cold dilute aquous sodium hydroxide

Answer 26

• 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

Question 27

What are the benefits and risks of using chlorine

Answer 27

• 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

Question 28

Describe the carbonate test

Answer 28

• 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

Question 29

Describe the sulfate test

Answer 29

• 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)

Question 30

Describe the test and result for halide ions

Answer 30

• 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

Question 31

Describe the sequence of tests used for qualitative analysis and why

Answer 31

• 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

Question 32

How do you test for a mixture of ions

Answer 32

• 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

Question 33

How do you test for ammonium ions

Answer 33

• 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