halogens

physical properties of 1st 4 halogens?

F2 - pale yellow gas

Cl2 - pale green gas

Br2 - brown-orange liquid

I2 - grey solid

what happens to BP down the group?

increases as more vdw forces due to increase atom size + Mr

what happens to electronegativity down the group?

decreases as atom size increases, so distance between nucleus + bonding electrons increases

what happens to shielding down the group?

increases

how does oxidation properties of the elements change down the group?

become more oxidising

what happens to reactivity down the group?

decreases as atom size increases so attraction to nucleus get weaker, so is harder to gain electron

when do halogens displace halides from a solution?

if the halide is lower in the periodic table

addition of chlorine water to potassium chloride solution?

no reaction

addition of chlorine water to potassium bromide solution?

orange Br solution and Cl^- ions made

addition of chlorine water to potassium iodide solution?

brown I solution and Cl^- ions made

addition of bromine water to potassium chloride solution?

no reaction

addition of bromine water to potassium bromide solution?

no reaction

addition of bromine water to potassium iodide solution?

brown I solution and Cl^- ions made

what dos iodine solution displace?

none because it is below all the elements

displacement reaction of chlorine water with bromide solution?

Cl2 + 2Br → 2Cl^- + Br2

displacement reaction of chlorine water with iodide solution?

Cl2 + 2I → 2Cl^- + I2

how is bleach made?

disproportionate reaction between chlorine and sodium hydroxide

chemical name of bleach?

sodium chlorate (I)

equation for bleach formation?

2NaOH + Cl2 → NaClO + NaCl + H2O

why is bleach formation a disproportionate reaction?

chlorine is simultaneously oxidised and reduced so overall oxidation state is 0

uses of bleach?

treat water
bleaching paper/fabrics
cleaning agents

how does water sterilisation kill bacteria?

produces chlorate ions [ClO-] which kill bacteria

formula for water sterilisation?

H2O + Cl2 → 2H⁺ + Cl^- + ClO^-

what happens when sunlight decomposes chlorinated water?

no chlorate ions are made, so bacteria cannot be killed

equation for decomposition of chlorinated water?

H2O + Cl2 → 2H⁺ + 2Cl^-

advantages of chlorinating drinking water?

• destroys bacteria

• long lasting so reduces bacteria build up

• reduces algae growth that discolours + gives water a bad taste

• prevents cholera

disadvantages of chlorinating drinking water?

• Cl gas toxic - bad for respiratory system

• liquid Cl can causes chemical burns

• Cl can react w/ organic compounds in water to make potentially carcinogenic chloroalkanes

how does ionic radius of ions change down the group?

increases as greater distance between nucleus + outer electron
more shielding
weak attractive force

how does reducing power of halogens change down the group?

increases as greater ionic radius so outer e- lost more readily

how to test for halide ions?

• add dilute nitric acid [HNO3]

• add silver nitrate solution [AgNO3]

• add ammonia solution to precipitates to confirm

what shows positive test for chloride ions with silver nitrate?

white precipitate [silver chloride]

what shows positive test for iodide ions with silver nitrate?

yellow precipitate [silver iodide]

what shows positive test for bromine ions with silver nitrate?

cream precipitate [silver bromide]

why is nitric acid added before silver nitrate?

to react w/ other anions aside from halogens to avoid a false result

what happens to Cl white precipitate when ammonia is added?

dissolves in dilute ammonia

what happens to Br yellow precipitate when ammonia is added?

dissolves in concentrated ammonia

what happens to I cream precipitate when ammonia is added?

insoluble in concentrated ammonia

how to test for group 2 ions in solid compounds?

• dip nichrome wire into concentrated HCl

• dip into sample

• place loop into blue bunsen flame + observe colour

what colour indicates presence of Ca2+?

dark red

what colour indicates presence of Sr2+?

red

what colour indicates presence of Ba2+?

green

how to test for ammonium compounds?

• add sodium hydroxide

• gently heat

• ammonia gas if ammonia present

• test gas w/ litmus paper

how is ammonia gas tested?

damp red litmus paper

ammonia dissolves in water and turns paper blue

how to test for hydroxides?

turns red litmus paper blue

further tests done to confirm as all alkalines turn it blue

test for carbonates?

• add HCl

• CO2 should be produced

• test by bubbling gas though limewater

• CO2 turns it cloudy

test for sulphates?

• add HCl to remove any carbonates which may precipitate + ruin result

• add barium chloride

• white precipitate = positive result

in the test for sulphates, what is the white precipitate?

insoluble barium sulphate

equation for formation of barium sulphate in test for sulphates

Ba²⁺ + SO₄^-2 → BaSO₄

what order should ions be tested in?

1. carbonates

2. sulfates

3. halides