halogens

EQ’s

state what is meant by disproportionation and use oxidation numbers to show that a reaction has taken place

disproportionation is oxidation and reduction of the same element

… is oxidised from .. to ..

.. is reduced from … to ..

Explain why halogens show this trend in BPs

Trend is down the group

London forces increase

Number of electrons increases

More energy is needed to break London IMFs

Explain the trend in BPs of the halogens

Halogens have weak London IMFs between molecules

BPs of halogens increased down the group because down the group the number of electrons increases , so the strength of London IMFs increases, down the group London IMFs are stronger so more energy is needed to break/ overcome London IMFs

Benefit of using chlorine in water treatment

Kills bacteria

Risk of using chlorine in water treatment

Forms chlorinated hydrocarbons

forms carcinogens/ toxic compounds

Toxic/ poisonous

Students adds a solution of bromine in an organic solvent to two test tubes (Br2), one test tube contains NaCl (aq) the other contains nano (aq) , student shakes the mixture allows them to settle and records the colour of the organic layer in each mixture

Sodium chloride: colour of organic layer is orange —> orange contains bromine so no reaction occurs

Sodium iodide: colour of organic layer is violet —> violet contains iodine

Ionic equation of the reaction that has occurred: Br2 + 2I- —→ 2Br- + I2

Students adds a solution of bromine in an organic solvent to two test tubes (Br2), one test tube contains NaCl (aq) the other contains nano (aq) , student shakes the mixture allows them to settle and records the colour of the organic layer in each mixture

Down the group reactivity decreases , oxidising power decreases , halogens gain electrons less easily form 1- ions less easily

Because down the group atomic radius increases there is greater atomic radius, more shells , more shielding

Less nuclear attraction down the group

Suggest why chlorine is added to water in large scale water treatment plans

Killing bacteria

Sea water contains aqueous bromide ions , chloride is used to extract bromine from sea water, explain why chlorine is suitable for this extraction of bromine but iodine is not

Cl2 + 2Br- —> 2Cl- + Br2

Chlorine is more reactive than bromine, iodine is less reactive than bromine

Chlorine is a stronger oxidant agent than bromine, iodine is a weaker oxidising agent than bromine

Explain why chlorine is more reactive than iodine

chlorine has smaller atomic radius (chlorine atom is smaller)

outer shell of chlorine is less shielded, closer

Chlorine has greater nuclear attraction SO

chlorine gains electrons less easily more easily, attracts an electron to its outer shell more easily, forms negative ion more easily

Chlorine gas reacts with dilute NaOH, this is a disproportionation reaction

Cl2 + 2NaOH —> H2O + NaCl + NaClO

Chlorine reacts with sodium hydroxide to form bleach state the conditions needed for this reaction

cold and dilute sodium hydroxide

A student bubbles chlorine gas through potassium iodide solution, a reaction takes place state what the student would observe

The solution would turn brown

For the ionic equation everything is aq except the Cl2 (g) at the start

Adding aqueous AgNO3 to aq solution of Br- ions and then a volume of dilute aq NH3 state what the student would see in the test tube

Cream precipitate

Outline a practical test that would confirm the presence of chloride ions in the lower layer and give the expected result

Add a few drops of aq silver nitrate, white precipitate forms

Apparatus used to separate the two liquid layers present at the end of the experiment

Separating funnel

Student is supplied with aq solutions of ionic compounds B and C

Compound B is a chloride,bromide or iodide of a group 1 element

Compound C is a chloride, bromide or iodide of a group 2 element

Show how the students could identify the halide present in B and C

Add aqueous silver nitrate AgNO3 (aq)

Chloride (Cl-) gives white precipitate

Bromide (Br-) gives cream precipitate

Iodide (I-) gives yellow precipitate

Give the equation for each: Ag+ (aq) + X- (aq) —> AgX (s)

An aq solution contains a mixture of Cl-, Br- and I- ions, AgNO3 (aq) is added to the mixture followed by an excess of dilute NH3 (aq) the resulting mixture is filtered which compounds are present in the residue on the filter paper l

AgBr and AgI

Which silver compound is insoluble in concentrated NH3 (aq)

AgCl

Explain why iodine is less reactive than bromine

Iodine has a larger atomic radius

Iodine has greater shielding/ more shells

Iodine has weaker/ less nuclear attraction on electrons gained than bromine

Bromine disproportionates when it reacts with potassium hydroxide solution suggest a formula for this reaction

Br2 + KOH —> Kane + KBrO + H2O