Group 7

Question 1

Colours of 4 main halogens at room temp & pressure

Answer 1

• F - pale yellow (g)
• Cl - green (g)
• Br - red/brown (l)
• I - grey (s)

Question 2

Describe and explain trends in Boiling Points

Answer 2

• Increses down group
• incresing strength of Van Der Waals force
• due to increasing number of electrons
• more energy needed to break force

Question 3

Describe and explain trends in Electronegativity

Answer 3

• Decreases down group
• greater atromic radius as outer electrons are further from nucleus
• greater nuclear charge and shielding
• Reduced attraction between electrons and nucleus

Question 4

Oxidising power trend in group 7

Answer 4

• Less reactive Down group
• outer electron further from nucleus
• Less powerful oxidising agent

Question 5

Describe how halogens act as Oxidising Agents in a displacement reaction

Answer 5

• halogen displaces halide = halide is below halogen in periodic table

Question 6

Displacement trend of halogens and halides

Answer 6

• Chlorine displaces Br- and I-
• Bromine displaces I-
• Iodine has no reaction with F-, Cl-, Br

Question 7

What is the ionic equation for a displacement reaction Using Chlorine

Answer 7

Cl2 (aq) + 2X- (aq) → 2Cl- (aq) + X (aq)

Question 8

What is the ionic equation for a displacement reaction Using Bromide

Answer 8

Br2 (aq) + 2I- (aq) → 2Br- (aq) + I (aq)

Question 9

Name all halide solutions with their colours

Answer 9

• Potassium Chloride KCl (aq) - colourless
• Potassium Bromide KBr (aq) - colourless
• Potassium iodide KI (aq) - colourless

Question 10

Halide displacement reaction in Chlorine water solution

Answer 10

Chlorine water - colourless
* KCl - no reaction
* KBr - orange solution (Br2)
* KI - brown solution (I2)

Question 11

Halide displacement reaction in Bromine water solution

Answer 11

Bromine Water - Orange
* KCl - no reaction
* KBr - no reaction
* KI - brown solution (I2)

Question 12

Halide displacement reaction in Iodine Solution

Answer 12

Iodine Solution - Brown
* KCl - no reaction
* KBr - no reaction
* KI - brown solution (I2)

Question 13

Name 2 uses of Chlorine

Answer 13

1. Kill bacteria in water
2. To make bleach

Question 14

What type of reaction is needed in the uses of chlorine?

Answer 14

A dispropotionation reaction

Question 15

Define Disporoprtionation reaction

Answer 15

A redox reaction in which atoms of the same element are both oxidised and reduced

Question 16

Write the equation of chloring and water

Answer 16

Cl2 (g) + H2O (l) → HClO (aq) + HCl (aq)

Question 17

Oxidation state of chlorine in:
* HClO
* HCl

Answer 17

• HClO: +1
• HCl: -1

Question 18

Ox. state equation of chlorine with water

Answer 18

Cl2 (g) + H2O (l) → 2H+ (aq) + Cl- (aq) + ClO- (aq)

Question 19

Oxidation state of Chlorine in Ox. state equation of Chlorine and water

Answer 19

• Cl2 = 0
• Cl- = -1
• ClO- = +1

Question 20

Benefits of Chlorine as water treatment

Answer 20

• Kills diseases causing bacteria
• Prevents water borne diseases (e.g. Cholera)
• Prevents algae growth which removes bad tatse, bad smell, discolouration

Question 21

Risks of using Chlorine as water treatment

Answer 21

• Chlorine is a toxic gas - irritates respiratory system if breathed in
• Toxic liquid - chemical burns on skin/eyes

Question 22

Smallest risk of chlorine as water treatment

Answer 22

• Chlorinated hydrocarbons could be produced which are carcinogenic
• however benefits outweigh this risk

Question 23

Conditions needed to make bleach

Answer 23

• Chlorine gas
• Cold & Dilute Aqeous Sodium Hydroxide

Question 24

Equation for chlorine and sodium hydroxide

Answer 24

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

Question 25

Oxidation states of Chlorine in: * NaClO * NaCl

Answer 25

* NaClO: +1 * NaCl: -1

Question 26

Reducing Power trend of halides

Answer 26

* Increases down the group * easier to lose electrons as attraction gets weaker * ions get bigger so electrons further away from nucleus * more shileding due to

Question 27

Write the equation for reaction of NaF/NaCl with H2SO4

Answer 27

* NaF (s) + H2SO4 (l) → NaHO4 (s) + HF (g) * NaCl (s) + H2SO4 (l) → NaHO4 (s) + HCl (g)

Question 28

Explain why the reaction stops NaF/NaCl with H2SO4

Answer 28

* HF/HCl formed - not strong enough reducing agent to reduce sulfuric acid * Not redox reaction - Halide (-1) and sulfur (+6) Ox. states stay same

Question 29

Write the equations of reaction of NaBr with H2SO4

Answer 29

1. NaBr (s) + H2SO4 (l) → NaHSO4 (s) + HBr (g) 2. 2HBr (g) + H2SO4 (l) → Br2 (g) + SO2 (g) + 2H2O (l)

Question 30

In the **second** equation of reaction between HBr and H2SO4, what are the Ox. states of: * Sufur * Bromide

Answer 30

* Sufur: +6 to +4 (reduction) * Bromide: -1 to 0 (Oxidation)