C10. The Halogens

Question 1

What are the trends going down group 7?

Answer 1

Boiling point increases - More van der waals forces, increasing size and relative mass of atoms; Physical states go from gas to solid; Electronegativity decreases - Atomic radius increases, shielding increases; Less oxidising; Less reactive - Atomic radius increases

Question 2

What are the physical appearances of F2, Cl2, Br2, I2?

Answer 2

F2, pale yellow gas; Cl2, pale green gas; Br2, brown-orange liquid; I2, grey solid

Question 3

What is the prerequisite for displacement reactions to occur with halogens?

Answer 3

Halogen will displace halide ion if halide ion is less reactive (lower in the periodic table)

Question 4

What is the half equation and observations of addition of chlorine water to potassium bromide?

Answer 4

Orange solution, Br2 formed;

Cl2 + 2Br- => 2Cl- + Br2

Question 5

What is the half equation and observations of addition of chlorine water to potassium iodide solution?

Answer 5

Brown solution, I2 formed; Cl2 + 2I- => 2Cl- + I2

Question 6

What is a disproportionation reaction?

Answer 6

A reaction where a compound is simultaneously reduced and oxidised

Question 7

How is bleached created?

Answer 7

Disproportionation reaction; Mixing chlorine and sodium hydroxide will form sodium chlorate(I) solution (bleach)
2NaOH(aq) + Cl2(g) => NaClO(aq) + NaCl(aq) + H2O(l)

Question 8

What are the uses of Sodium Chlorate(I)?

Answer 8

Treating water; Bleaching fabric, papers; Cleaning agent

Question 9

How does chlorine sterilise water and what is the equation?

Answer 9

Water + Chlorine = Chlorate(I) ions which kill bacteria;

H2O(l) + Cl2(g) => 2H+(aq) + Cl-(aq) + ClO-(aq); Disproportionation reaction;

Question 10

Why does chlorine have to be regularly replaced in swimming pools (use an equation to prove)?

Answer 10

Sunlight decomposes chlorinated water, no chlorate(I) ions produced;2H2O(l) + Cl2(g) => 4H+(aq) + 2Cl-(aq) + O2(g)

Question 11

What are the advantages of chlorinating water?

Answer 11

Destroys microorganisms; Long lasting, reduces bacteria build up; Reduce growth of algae which discolour water and give it bad tase and smell

Question 12

What are the disadvantages of chlorinating water?

Answer 12

Chlorine gas is toxic and irritates respiratory system; Liquid chlorine causes severe chemical burns; Chlorine can react with organic compounds formine chloroalkanes , linked to causing cancer

Question 13

Are halide ions oxidising or reducing and why?

Answer 13

Reducing; Halogens gain an electron becoming -1 halide ions; Extra electron is removed

Question 14

What are the trends in ions going down group 7?

Answer 14

Ionic radius increases; Distance between nucleus and outer electron increases; More shielding; Attractive forces get weaker; Outer electron more readily lost; I- stronger reducing agent than F-

Question 15

How do chlorine level chlorides react with concentrated sulfuric acid?

Answer 15

Not redox reaction; NaCl, NaBr, NaI react same first stage;

H2SO4 + NaCl => NaHSO4 + HCl; White misty fumes produced

Question 16

How do bromide level ions react with concentrated sulfuric acid?

Answer 16

Redox reaction; I-, Br- react same second stage;
2Br- => Br2 + 2e- (Br is oxidised)
H2SO4 + 2H+ + 2e- => SO2 + 2H2O (S is reduced)
H2SO4 + 2H+ +2Br- => SO2 + Br2 + 2H2O (overall ionic); In addition to NaBr; Orange vapour of Br2 produced

Question 17

How do Iodide level ions react with concentrated sulfuric acid?

Answer 17

In addition to NaI, I2;
6I- => 3I2 + 6e- (I- ion oxidised)
H2SO4 + 6H+ + 6e- => S + 4H2O (S being reduced)
H2SO4 + 6H+ 6I- => 3I2 + S + 4H2O (overall ionic); Yellow solid produced (S);
8I- => 4I2 + 8e- (I- oxidised)
H2SO4 + 8H+ + 8e- => H2S + 4H2O (S being reduced)
H2SO4 + 8H+ + 8i- => 4I2 + H2S + 4H2O (overall ionic); Rotten egg smell (H2S)

Question 18

What is the test for identifying halide ions?

Answer 18

Add dilute nitric acid (HNO3 reacts with any anions aside aside from halides); Add silver nitrate solution (AgNO3); Cl ions white precipitate, Br ions cream precipitate, I ions yellow precipitate; Add ammonia solution (NH3); Cl- dissolves in dilute NH3; Br dissolves in concentrated NH3; I- insoluble in concentrated NH3

Question 19

What is the test for group 2 anions?

Answer 19

Dip nichrome wire in concentrated HCl; Dip into sample; Place loop into blue bunsen flame; Ca2+ dark red, Sr2+ red, Ba2+ green

Question 20

What is the test for ammonia compounds?

Answer 20

Add NaOH, gently heat; NH3 gas produced; Test w/ damp red litmus paper; NH3 will dissolve in water and turn litmus blue;
NH4+(aq) + OH-(aq) => NH3(g) + H2O(l)

Question 21

What is the test for hydroxides?

Answer 21

Hydroxides are alkaline; Turn red litmus paper blue; Not definitive; Red litmus turns blue in any alkali, further tests are needed

Question 22

What is the test for carbonates?

Answer 22

HCl reacts with carbonates to form CO2(g); Bubble through limewater, turns cloudy;
CO3(2-) + 2H+ => CO2 + H2O

Question 23

What is the test for sulfates?

Answer 23

Add HCl to remove carbonates; Add Barium Chloride; White precipitation (BaSO4);
Ba(2+)(aq) + SO4(-2)(aq) => BaSO4(s)

Question 24

What is the order to tests unknown ions in?

Answer 24

Test for carbonates, CO2(g) produced?; Test for sulfates, BaSO4 precipitate?; Test for halides. white, cream, yellow precipitates?