Group 7

Question 1

Fluorine at room temperature

Answer 1

• Yellow poisonous gas

Question 2

Chlorine at room temperature

Answer 2

• Green poisonous gas

Question 3

Chlorine in aqueous solution

Answer 3

• Pale green solution / colourless in low concentrations

Question 4

Bromine at room temperature

Answer 4

Brown vapour or red/brown liquid

Question 5

Bromine in aqueous solution

Answer 5

• Orange solution

Question 6

Iodine at room temperature

Answer 6

Grey / black solid sublimes to purple vapour

Question 7

Iodine in aqueous solution

Answer 7

• Brown solution

Question 8

Reaction of chlorine with water to form chloride ions and chlorate (I) ion

Answer 8

Cl2 + H2O —> HCl + HClO

Gives bleaching power of wet chlorine

Disproportionation reaction

Question 9

Chloric (I) acid to make chlorate ions equation

Answer 9

HClO + H2O —> ClO- + H3O+ or H+

Question 10

Chlorine and water in sunlight equation

Answer 10

2Cl2 + 2H2O —> 4HCl + O2

Question 11

Chlorine with cold dilute NaOH equation

Answer 11

Cl2 + NaOH —> NaCl + NaClO + H2O

Sodium chlorate used as bleach

Disproportionation reaction

Question 12

What can HCl and HClO be used for?

Why can Cl2 be used since it’s toxic?

Answer 12

• Both kill bacteria in drinking water or swimming pools in low concentrations
• Cl2 used as benefits outweigh the potential health risks to humans

Question 13

Why are fluoride ions added to water?

Answer 13

To prevent tooth decay as they strengthen enamel

Question 14

Chlorine with NaBr ionic equation and results

Answer 14

• Cl2 + 2Br- —> Br2 + 2Cl-
• Br2 released so orange colour observed

Question 15

Chlorine with NaI ionic equation and results

Answer 15

• Cl2 + 2I- —> I2 + 2Cl-
• Brown colour observed

Question 16

Bromine with NaCl and NaBr

Answer 16

No reaction

Question 17

NaCl with Cl2

Answer 17

No reaction

Question 18

Bromine with NaI ionic equation and results

Answer 18

• Br2 + 2I- —> I2 + 2Br-
• Brown colour observed

Question 19

Iodine with NaCl, NaBr or NaI

Answer 19

No reaction

Question 20

Strength of oxidising agent down group 7

Answer 20

Decreases down, iodine is the weakest oxidising agent because fluorine smallest ion so electrons most strongly held by the nucleus compared to other ions / less shielding

Question 21

Reduction equation of Cr2O7(2-)

Answer 21

Cr2O7(2-) + 6e- + 14H+ —> 2Cr(3+) + 7H2O

Question 22

Reduction equation of MnO4

Answer 22

MnO4 + 5e- + 8H+ —> Mn2+ + 4H2O

Question 23

Reduction equation of MnO2

Answer 23

MnO2 +2e- + 4H+ —> Mn2+ +2H2O

Question 24

Reduction equation of H2SO4 to SO2

Answer 24

H2SO4 + 2e- + 2H+ —> SO2 + 2H2O

Question 25

Colour change of KMnO4 if reduction has occured

Answer 25

* Purple solution will turn pink (or colourless with a dilute solution)

Question 26

Colour change of K2Cr2O7 is reduction has occured

Answer 26

* Orange solution turns green

Question 27

S(2-) to SO4(2-) oxidising equation

Answer 27

S2- + 4H20 ---\> SO4(2-) + 6e- + 8H+

Question 28

Test for HCl, HBr and HI

Answer 28

Damp blue litmus paper will turn red * All hydrogen halides produce white misty fumes

Question 29

Reaction of H2SO4 and sodium halide equation and which react further

Answer 29

* H2SO4 + NaCl ---\> NaHSO4 + HCl * H2SO4 + NaF ---\> NaHSO4 + HF * H2SO4 + NaBr ---\> NaHSO4 + HBr * H2SO4 + NaI ---\> NaHSO4 + HI Only NaBr and NaI react further as they are strong enough reducing agents and can reduce sulfuric acid

Question 30

Strength of reducing agents down the group

Answer 30

* Increases down group * Iodine strongest reducing agent and fluorine the weakest

Question 31

NaBr + H2SO4 full overall equation

Answer 31

2NaBr + 3H2SO4 ---\> 2NaHSO4 + SO2 + 2H2O + Br2

Question 32

NaBr + H2SO4 ionic equation

Answer 32

2Br- + H2SO4 + 2H+ ---\> Br2 + SO2 + 2H2O

Question 33

Why are there 3 potential reactions with NaI and H2SO4

Answer 33

I- is a stronger reducing agent

Question 34

Give the ionic equation and full equation of the reaction with H2SO4 that gives a pruple vapour (I2) and black solid (I2)

Answer 34

* 2I- + H2SO4 + 2H+ ---\> I2 + SO2 + 2H2O * 2NaI + 3H2SO4 ---\> 2NaHSO4 + SO2 + 2H2O + I2

Question 35

Give full equation and ionic equation for reaction with H2SO4 that produces a yellow solid

Answer 35

* 6I- + H2SO4 + 6H+ ---\> 3I2 + S + 4H2O * 6NaI + 7H2SO4 ---\> 6NaHSO4 + S + 4H2O + 3I2

Question 36

Give the full equation and ionic equation of reaction with H2SO4 that produces a rotten egg smell

Answer 36

* 8I- + H2SO4 + 8H+ ---\> H2S + 4I2 + 4H2O * 8NaI + 9H2SO4 ---\> 8NaHSO4 + H2S + 4H20 + 4I2

Question 37

Test for H2S

Answer 37

With lead nitrate paper makes lead sulfide and nitric acid, so paper goes black as black insoluble compound * H2S (g) + Pb(NO3)2 (aq) ---\> PbS (s) + 2HNO3 (aq)