Chemistry- Group 17

what molecules are the halogens known as

diatomic molecules, easiest way to complete shells is to form covalent bonds

what are the trends in melting point and boiling point of group 17, explain why

as relative molecular mass increases so does the melting and boiling point. ID-ID forces exist between the molecules, as you go down the group there are more electrons, meaning more chances of ID-ID forces emerging

define volatility

the ease at which a substance evaporates

what is the order of volatility of halogens

iodine<bromine<chlorine<fluorine

list the appearance of the halogens at room temperature

F2= pale yellow gas at room temp, Cl2= pale green gas at rtp, Br2= red-brown liquid at rtp, I2=grey solid with purple vapour at rtp

why are halogens oxidising agents

because they only need to gain 1 more electron to create a stable configuration, gaining an electron makes them an oxidising agent

which element is the strongest oxidising agent

Fl because it is the best at accepting electrons

what is the trend of oxidising power of the halogens and why

it decreases going down the group, this is because atoms are experiencing higher shielding effect, electrons are not as attracted to atoms = lower electronegativity

what reaction is an example of how halogens are oxidising agents and how

displacement reaction, example of redox reactions

how do halogen displacement reactions occur

a more reactive halogen displaces a less reactive halogen from a halide solution of the less reactive halogen

how can you detect if a displacement reaction occurs, and what are the specific examples of this

by observing a colour change: chlorine solution = colourless, bromine solution = orange, iodine solution = brown

what can be used to make halide displacement reactions clearer and why

cyclohexane, cyclohexane = polar solvent water = non polar solvent, halide ions will dissolve in the water whilst halogens will dissolve in cyclohexane —> creates two distinct layers

what is the general equation for halogens reacting with hydrogen

X2 (g) + H2 (g) —> 2HX (g)

describe the nature of the reactions between halides and hydrogen, and why the reactions are like this

HF: reacts explosively in all conditions, HCl: reacts explosively in sunlight, HBr: reacts slowly upon heating, HI: forms an equilibrium mixture upon heating

• the reactions are like this because reactivity decreases down the group

describe the thermal stability of the halogen hydrides and why

thermal stability decreases down the group, the halogen atom gets bigger, the overlap of its outer shell with hydrogen gives a longer bond length = weaker bond energies, easier to break

define thermal stability

the resistance of a compound to breakdown by heating

define disproportionation

the simultaneous oxidation and reduction of the same species in a chemical reaction

example of a disproportionation reaction and what happens during this reaction

when chlorine reacts with a dilute alkali, chlorine atoms are oxidised and reduced in the same reaction

what is the reducing power of the halides going down the group and why

the reducing power increases down the group, as they are getting oxidised and are losing electrons, this is because halide ions increase in size going down the group, more shielding, electrons from outer shells are easier to remove

how can a halide be identified in an unknown solution

dissolving solution in nitric acid, adding silver nitrate, followed by an ammonia solution

what is the general and ionic equation for halides reacting with silver nitrate solution

General equation:   AgNO₃ (aq) + X^– (aq) → AgX (s) + NO₃^– (aq)

Ionic equation:   Ag⁺ (aq) + X^– (aq) → AgX (s)

what does the formation of each type of ppt formed from adding silver nitrate indicate

white ppt: AgCl forms if chloride ions are present

cream ppt: AgBr forms if bromide ions are present

yellow ppt: AgI forms if iodide ions are present

why is ammonia added after silver nitrate

because the ppt from silver nitrates are hard to differentiate between

what does it mean if the ppt dissolves from addition of dilute ammonia

halide present is chlorine

what does it mean if ppt dissolves with the addition of concentrated ammonia

halide present = bromide

what does it mean if the ppt doesn’t dissolve from dilute or conc ammonia

iodide present

why should the reactions of the halides with sulfuric acid be carried out in a fume cupboard

because these reactions produce toxic gases

what is the general reaction of the halide ions with concentrated sulfuric acid

H₂SO₄ (aq) + X^– (aq) → HX (g) + HSO₄^– (aq)

how do you react chloride ions with sulfuric acid, what gas does it produce and what colour is it?

compounds with Cl- ions react to sulfuric to form HCl and a salt produces HCl gas and it is white

what is the equation for chloride ions with sulfuric acid

NaCl (s) + H₂SO₄(l) → NaHSO₄(s) + HCl(g) 

what is the reaction for bromide ions with sulfuric acid

at first it forms hydrogen bromide, BUT this is then oxidised by the sulfuric, this then turns into bromide, sulfur dioxide and water

write the two equations for bromide ions reacting with sulfuric acid

1) NaBr(s) + H₂SO₄(l) → NaHSO₄(s) + HBr(g)

2) 2HBr(g) + H₂SO₄ (l) → Br₂(g) + SO₂(g) + 2H₂O(l)

how do iodide ions react with conc sulfuric acid

originally forms hydrogen iodide, but this is then oxidised by the sulfuric

which is the better reducing agent, HI, HBr

HI

write out the reactions for iodide ions with sulfuric acid

Initial reaction: 

NaI(s) + H₂SO₄(l) → NaHSO₄(s) + HI(g)

Followed by: 

2HI(g) + H₂SO₄(l) → I₂(g) + SO₂(g) + 2H₂O(l) I₂ is purple/violet vapour

6HI(g) + H₂SO₄(l) → 3I₂(g) + S(s) + 4H₂O(l) S is a yellow solid

8HI(g) + H₂SO₄(l) → 4I₂(g) + H₂S(g) + 4H₂O(l) H₂S smells like rotten eggs

write the reaction + ionic reaction of a chlorine and cold alkali (15 degrees)

Cl₂ (aq) + 2NaOH (aq) → NaCl (aq) + NaClO (aq) + H₂O (l)

• The ionic equation is:

Cl₂ (aq) + 2OH^– (aq) → Cl^– (aq) + ClO^– (aq) + H₂O (l)

what are the half equations for the reduction and oxidation of chlorine in this reaction

oxidation: ½Cl₂ (aq) + 2OH^– (aq) → ClO^– (aq) + H₂O (l) + e^–

^reduction: ½Cl₂ (aq) + e^– → Cl^– (aq)

write the equation that takes place when chlorine reacts with hot alkali (70 degrees)

3Cl₂ (aq) + 6NaOH (aq) → 5NaCl (aq) + NaClO₃ (aq) + 3H₂O (l)

write out the half reactions or when chlorine gets reduced and oxidised

oxidation: ½Cl₂ (aq) + 6OH^– (aq) → ClO₃^– (aq) + 3H₂O (l) + e^–

^reduction: ½Cl₂ (aq) + e^– → Cl^– (aq)

what can chlorine be used for with water

to make it drinkable, and clean

is the reaction between chlorine and water a disproportionation reaction

yes

write the equation for chlorine reacting with water

Cl₂ (aq) + H₂O (l) ⇌ HCl (aq) + HClO (aq)

write the half equations for oxidation and reduction of chlorine when reacting with water

oxidation: ½Cl₂ (aq) + 2OH^– (aq) → ClO^– (aq) + H₂O (l) + e^–

^reduction: ½Cl₂ (aq) + e^– → Cl^– (aq)

how does chlorine act as a steriliser for water

it kills bacteria, specifically the chloric acid HClO

how does chloric acid further dissociate

HClO (aq) → H⁺ (aq) + ClO^- (aq)