3.2.3- Group 7(17), the halogens (PAPER 1)

Question 1

What is the trend in atomic radius down Group 7?

Answer 1

Atomic radius increases due to combined effect of an increase in number of shells and shielding being greater than increase in + charge.

Question 2

What is the trend in electronegativity down Group 7?

Answer 2

Electronegativity decreases down the group as atomic radius and shielding increases (added electron shells) so bonding pair of electrons in the covalent bond are further from the positively charged nucleus.

Less electrostatic attraction between nucleus and bonding pair of electrons.

Question 3

What is the trend in melting/boiling point down Group 7?

Answer 3

Melting+ boiling points increase as the number of electrons in each molecule is increasing, increasing the number/ strength of van der waal’s forces between the moleucles, it is harder to separate one molecule from another.

Question 4

What is the trend in ionisation energy down Group 7?

Answer 4

Ionisation energy decreases as there is more shielding and atoms get bigger, so weaker attraction between nucleus and electron in outer shell.

Question 5

How do halogens act as oxidising agents + general equation.

Answer 5

Halogen molecules react by gaining electrons from other substances.

X2 + 2e- ——> 2X-

Halogen molecule has been reduced as it has gained electrons, it has oxidised the other substance.

Question 6

How is oxidising ability of halogens shown in reaction between sodium and chlorine?

Answer 6

2Na (s) + Cl2 (g) —- 2NaCl (s)

Chlorine oxidises the sodium from state 0 to +1

Chlorine is reduced from 0 to -1

Question 7

What is the trend in oxidising ability of halogens down Group 7?

Answer 7

Oxidising power of halogens decreases down group 7.

AND

Ability of a halogen molecule to be reduced decreases.

Number of energy levels increases, atomic radius increases, shielding increases between outer shell electrons and nucleus so larger atoms attract extra electron less strongly.

Question 8

What occurs in halogen-halide displacement reactions?

Answer 8

Redox reaction occurs when more reactive halogen nearer the top displaces a less reactive halide ion from its aqueous compound and oxidises it.

Question 9

What occurs when chlorine water is added to potassium chloride solution?

Answer 9

No reaction as they are just as reactive.

COLOURLESS/ PALE GREEN (CL2)

Question 10

What occurs when chlorine water is added to potassium bromide solution?

Answer 10

Chlorine is more reactive than a bromide ion so displaces it.

ORANGE/YELLOW SOLUTION (BR2) MADE

Cl2+ 2Br—-> 2Cl- + Br2

Question 11

What occurs when chlorine water is added to potassium iodide solution?

Answer 11

Chlorine is more reactive than an iodide ion so displaces it.

BROWN SOLUTION (I2) MADE

Cl2 + 2I- —–> 2Cl- + I2

Question 12

What occurs when bromine water added to potassium chloride solution?

Answer 12

No reaction as bromine is less reactive than chloride ions.

ORANGE/YELLOW SOLUTION (BR2) MADE

Question 13

What occurs when bromine water added to potassium bromide solution?

Answer 13

No reaction as bromide ions and bromine are just as reactive.

ORANGE/YELLOW SOLUTION (BR2) MADE

Question 14

What occurs when bromine water added to potassium iodide solution?

Answer 14

Bromine is more reactive than an iodide ion so displaces it.

BROWN SOLUTION (I2) MADE

Br2 + 2I- —–> 2Br- + I2

Question 15

What occurs when iodine solution added to potassium chloride solution?

Answer 15

No reaction as iodine less reactive than chloride ions.

BROWN

Question 16

What occurs when iodine solution added to potassium bromide solution?

Answer 16

No reaction as iodine less reactive than bromide ions.

BROWN

Question 17

What occurs when iodine solution added to potassium iodide solution?

Answer 17

No reaction as iodine just as reactive as iodide ions.

BROWN

Question 18

What is the order of oxidising power of halogens?

Answer 18

F2 > Cl2 > Br2 > I2

Question 19

What occurs when Cl2 is bubbled through solution containing NaBr?

Overall equation and 2 half equations.

Answer 19

Cl2(aq) + 2NaBr (g) —-> 2NaCl (aq)+ Br2(aq)

Chlorine oxidises the bromide ions to aqueous bromine- Br2.

2Br- —-> Br2 + 2e- (redOX= OXIDATION electrons on right)
Cl2 + 2e- —-> 2Cl- (REDox = REDUCTION electrons on left)

Question 20

What is the trend in reducing ability of the halide ions?

Answer 20

Reducing ability of halides increases down the group as there are more electron energy levels, the shielding between outer electrons and nucleus increases so so there is a lower electrostatic attraction between nucleus and electrons.

It is easier to remove an electron from a halide ion down the group, they are more readily oxidised/ powerful reducing agents

Question 21

How to make hydrogen chloride using a halide salt and concentrated sulfuric acid (1 STEP)?

Answer 21

Concentrated sulfuric acid donates hydrogen ion to a chloride ion to make hydrogen chloride.

NaCl + H2SO4 ——> HCl + NaHSO4

white steamy fumes HCl

Question 22

What effect does the addition of H2SO4 to NaCl have on potassium dichromate paper and lead ethanoate paper?

Answer 22

No effect on either

Question 23

What effect does the addition of H2SO4 to NaBr have on potassium dichromate paper and lead ethanoate paper?

Answer 23

potassium dichromate paper turns green in the presence of SO2

lead ethanoate paper has no reaction

Question 24

What effect does the addition of H2SO4 to NaI have on potassium dichromate paper and lead ethanoate paper?

Answer 24

potassium dichromate paper turns green in the presence of SO2

lead ethanoate paper turns black in the presence of H2S

Question 25

How to make hydrogen fluoride using a halide salt and concentrated sulfuric acid (1 STEP)?

Answer 25

Concentrated sulfuric acid donates hydrogen ion to a fluoride ion to make hydrogen fluoride. NaF + H2SO4 -------> HF + NaHSO4 white steamy fumes HF

Question 26

Why do only acid-base reactions occur when using fluoride or chloride ions?

Answer 26

The H2SO4 is not strong enough an oxidising reagent to oxidise the chloride and fluoride ions so redox reactions occur.

Question 27

How to use bromide ions with concentrated sulfuric acid (2 STEPS)?

Answer 27

Br- ions are stronger reducing agents than Cl- and F- and after the initial acid- base reaction reduce the sulfur in H2SO4 from +6 to + 4 in SO2 Initial step the same: NaBr + H2SO4 -----> HBr + NaHSO4 -(H2SO4 acts as acid) 2nd redox step: 2HBr + H2SO4 ----> Br2 + SO2 + 2H2O -(H2SO4 acts as oxidising agent, the S is reduced from +6 to +4)

Question 28

What are the half equations for reaction of bromide ions with concentrated sulfuric acid? + Overall ionic

Answer 28

redOX 2Br-----> Br2 + 2e- REdox H2SO4 + 2 H+ + 2 e- ----> SO2 + 2 H2O overall ionic= H2SO4 + 2H+ + 2Br ----> Br2 + SO2 + 2H2O oxidation of Br-, reduction of H2SO4

Question 29

What are the observations for reaction of bromide ions with concentrated sulfuric acid?

Answer 29

White steamy fumes of HBr orange/ red fumes of Bromine, and a colourless, acidic gas SO2

Question 30

How to use iodide ions with concentrated sulfuric acid ( 2 STEPS) and what are observations?

Answer 30

I- ions are the strongest halide reducing agents. They can reduce the sulfur from +6 in H2SO4 to + 4 in SO2, to 0 in S and -2 in H2S. observations= white steamy fumes HI, purple flames I2, colourless acidic gas SO2, yellow solid S, eggy gas H2S Initial step the same: NaI(s) + H2SO4 (l) ----> NaHSO4 (s) + HI(g)

Question 31

What is the equation for the reduction of sulfur from +6 in H2SO4 to +4 in SO2 using iodide ions? AND 2 HALF EQUATIONS

Answer 31

2HI + H2SO4 ----> I2 + SO2 + 2H2O redOX (e- on right) 2I- ----> I2 + 2e- REdox (e- on left) H2SO4 + 2 H+ + 2 e- ----> SO2 + 2 H2O

Question 32

What is the equation for the reduction of sulfur from +6 in H2SO4 to 0 in S using iodide ions? AND 2 HALF EQUATIONS

Answer 32

6HI + H2SO4 ----> 3 I2 + S + 4 H2O redOX (e- on right) 2I- -----> I2 + 2e- REdox (e- on left) H2SO4 + 6H+ + 6e- -----> S + 4H20

Question 33

What is the equation for the reduction of sulfur from +6 in H2SO4 to -2 in H2S using iodide ions? AND 2 HALF EQUATIONS

Answer 33

8HI + H2SO4 ------> 4I2 + H2S + 4H2O redOX (e- on right) 2I- -----> I2 + 2e- REdox (e- on left) H2SO4 + 8H+ + 8e- -------> H2S + 4H20

Question 34

What are the steps for testing for halides using silver nitrate and ammonia?

Answer 34

1) Add dilute nitric acid (HNO3) to the solution in order to react with carbonates present to prevent formation of precipitate Ag2CO3. 2) Add silver nitrate solution (AgNO3) producing a precipitate for Cl-, Br- and I- ions. 3) Add dilute and concentrated ammonia to see if precipitates re-dissolve.

Question 35

What is a positive result for chloride ions?

Answer 35

white precipitate Ag+ (aq) + Cl- (aq) ---> AgCl(s)

Question 36

What is a positive result for bromide ions?

Answer 36

cream precipitate Ag+ (aq) + Br- (aq) ----> AgBr (s)

Question 37

What is a positive result for iodide ions?

Answer 37

pale yellow precipitate Ag+ (aq) + I- (aq) ----> AgI (s)

Question 38

What occurs when ammonia is added to the 3 halides?

Answer 38

AgCl- white precipitate dissolves in dilute NH3 AgBr- cream precipitate dissolves in concentrated NH3 AgI- yellow precipitate insoluble in NH3

Question 39

What is the trend in solubility of the silver halides in ammonia?

Answer 39

Decreases in the order: AgF > AgCl > AgBr > AgI

Question 40

How does chlorine react with cold water?

Answer 40

To produce chlorate (I) ions ClO- and chloride ions. Cl2 + H20 ----> HCl + HClO chloric acid can further dissociate in water to form.... Cl2 + H20 ----> ClO- + Cl- + 2H+ Chlorine oxidised from 0 in Cl2 to -1 in Cl-. Chlorine reduced from 0 in Cl2 to +1 in ClO-

Question 41

What can chloric acid (HClO) or chlorate ions (ClO-) be used for?

Answer 41

Sterilising water by killing bacteria.

Question 42

What is the reaction of chlorine in sunlight/UV?

Answer 42

Chlorine rapidly lost from pool water. No ClO- made Cl2 + 2H2O -----> 4H+ + 2Cl- + O2

Question 43

What are the benefits and limitations of using chlorine to sterilise water?

Answer 43

Benefits: destroys microorganisms that cause disease, long lasting reducing bacteria build up, reduces growth of algae that discolours water. Limitations: chlorine gas is toxic and irritates respiratory system, liquid chlorine causes chemical burns, chlorine can react with organic compounds in the water forming chloroalkanes.

Question 44

How does chlorine react with cold, dilute, sodium hydroxide?

Answer 44

Cl₂ (aq) + 2NaOH(aq) → NaOCl(aq) + NaCl(aq) + H₂O(l) chlorine is oxidised and reduced in a process known as disproportionation, forming sodium hypochlorite (NaOCl) and sodium chloride (NaCl).

Question 45

How does chlorine react with solid sodium chlorate?

Answer 45

NaClO + H2O ⇌ Na+ + OH- + HClO sodium dissolves in water to form chloric (I) acid. swimming pools need to be kept slightly acidic as otherwise equilibrium moves to left and HClO removed as ClO- ions.

Question 46

How is bleach made? + reaction

Answer 46

By a disproportionation reaction where chlorine has been reduced and oxidised. Cl= 0, +1, -1 2NaOH (aq) + Cl2 (g) -----> NaClO (aq) + NaCl (aq) + H2O (l) chlorine and sodium hydroxide form sodium chlorate (I) solution.