Topic 12- Intro to Redox and group 7, the halogens

Question 1

Oxidation

Answer 1

• Loss of electrons
• Gain of oxygen
• Loss of hydrogen
• Increase in oxidation state

Question 2

Reduction

Answer 2

• Gain of electrons
• Loss of oxygen
• Gain of hydrogen
• Decrease in oxidation state

Question 3

Oxidation state

Answer 3

The charge on a simple ion, or the difference in the number of electrons associated with an atom in a compound compared with the atoms of the element.

Question 4

Trends in electronegativity down group 7

Answer 4

Electronegativity decreases down the group.
- Atomic radius increases
- Shielding increases
- Bonded electrons are further from the attractive power of the nucleus.

Question 5

Trends in boiling point down group 7

Answer 5

Increases down the group.
- Mr increases down the group
- More electrons, means increased dipole-dipole attractions
- Greater VDWs between molecules
- More energy must be supplied to break the stronger IMFs.

Question 6

Trends in oxidizing abilities down group 7

Answer 6

The oxidizing ability of the halogens decreases down the group.
Cl>Br2>I2

Question 7

Chlorine water (Cl2) displacement reactions of halide ions in aqueous solution.

Answer 7

Cl2 + 2NaBr –> 2NaCl + Br2
- Chlorine displaces bromine from solution
- Colorless solution change to orange solution
Cl2 + 2NaI –> 2NaCl + I2
- Chlorine displaces iodine from solution
- Colorless solution changes to brown solution

Question 8

Bromine water (Br2) displacement reactions of halide ions in aqueous solution.

Answer 8

Br2 + 2NaI –> 2NaBr + I2
- Bromine displaces iodine from solution
- Colorless solution changes to brown solution

Question 9

Iodine solution (I2) displacement reactions of halide ions in aqueous solutions

Answer 9

No reactions

Question 10

Trend in reducing abilities down group 7

Answer 10

Reducing ability of halide ions increases down group 7.
- Iodine ions are strongest
- Ionic radius and shielding increase
-Attraction between nucleus and outer electron is reduced.

Question 11

Reactions of solid sodium halides with conc. H2SO4

Answer 11

Conc. H2SO4 acts as an oxidizing agent.
Halide ions acts as a reducing agent.

Question 12

Reaction of conc. H2SO4 with NaF (s)
(Fluoride ions aren`t strong enough to reduce the sulfur in H2SO4)

Answer 12

NaF + H2SO4 –> NaHSO4 + HF (not redox)
- products, sodium hydrogen sulfate and hydrogen fluoride.
- misty white fumes (HF)

Question 13

Reaction of conc. H2SO4 with NaCl (s)
(Chlorine ions aren`t strong enough to reduce the sulfur in H2SO4)

Answer 13

NaCl + H2SO4 –> NaHSO4 + HCl (not redox)
- products, sodium hydrogen carbonate and hydrogen chloride.
- misty white fumes (HCl)

Question 14

Reaction of conc. H2SO4 with NaBr (s)
(Bromide ions are better reducing agents and can reduce sulfur from +6 in H2SO4 to +4 in SO2) (Br is oxidized from -1 in HBr to 0 in Br2)

Answer 14

NaBr + H2SO4 –> NaHSO4 + HBr (not redox) 2HBr + H2SO4 –> Br2 + SO2 + 2H2O (redox)
- products, sodium hydrogen carbonate, hydrogen bromide, bromine, water and sulfur dioxide
- misty white fumes (HBr), red-brown vapor (SO2)

Question 15

Reaction of conc. H2SO4 with NaI (s)
(Iodide ions are the best reducing agent, and reduce the sulfur in sulf. acid to SO2, further to S and then to H2S)

Answer 15

NaI + H2SO4 –> NaHSO4 + HI (not redox)
- products, sodium hydrogen sulfate, hydrogen iodide
- misty white fumes (HI
2HI + H2SO4 –> I2 + SO2 + 2H2O (redox)
- products, iodine, water, sulfur dioxide
- purple vapour (I2)
6HI + H2SO4 –> 3I2 + S + 4H20 (redox)
- products, iodine, sulfur, water
- yellow solid formed (S)
8HI + H2SO4 –> 4I2 + H2S + 4H2O (redox)
- products, iodine, hydrogen sulfide, water
- rotten egg smell (H2S) toxic gas

Question 16

Method for testing for halide ions

Answer 16

1- Make a solution of the compound using dilute nitric acid
2- Add silver nitrate solution and record the color of the precipitate
3- Add dilute or concentrated ammonia solution

Question 17

Why is dilute nitric acid added?

Answer 17

Removes other ions that would react with the silver ions in the silver nitrate solution.

Question 18

Testing for chloride ions (Cl-)

Answer 18

With silver nitrate solution - White ppt
Add dilute ammonia solution- White ppt dissolves to form colorless solution
Add conc. ammonia solution- white ppt dissolves to form colorless solution

Question 19

Testing for Bromide ions (Br-)

Answer 19

With silver nitrate solution- cream ppt
Add dilute ammonia solution- cream ppt remains
Add conc. ammonia solution- white ppt dissolves to form colorless solution

Question 20

Testing for Iodide ions (I-)

Answer 20

With silver nitrate solution- yellow ppt
Add dilute ammonia solution- yellow ppt remains
Add conc. ammonia solution- yellow ppt remains, is insoluble in conc. ammonia solution

Question 21

Reaction of chlorine with cold, dilute aqueous NaOH

Answer 21

Produces chlorate (I) ions, ClO-
2NaOH + Cl2 –> NaCl + NaClO + H2O
- green (cl) gas reacts to form a colorless solution
- Redox reaction, chlorine is oxidized from oxidation state of 0 in Cl2 to +1 in NaClO
- Chlorine is also reduced from 0 in Cl2 to -1 in NaCl

Question 22

Uses of Chlorate ion

Answer 22

The chlorate (I) ions are responsible for bleaching mechanism, it kills bacteria and micro-organisms. Used in bleach.

Question 23

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

Answer 23

Forms chloride ions and chlorate (I) ions
Cl2(g) + H2O(l) –> HCl + HClO (reversible)
- Cl slightly soluble in water and produces a pale green solution
- Some Cl react with water to form a mixture of HCl and HClO

Question 24

Reaction of chlorine and water to form chloride ions and oxygen

Answer 24

In the sunlight the chloric (I) acid decomposes into hydrochloric acid. The equation is:
Cl2 + 2H2O –> 4HCl + O2
This means chlorine is rapidly lost from pool water in sunlight.

Question 25

Benefits of why chlorine used in water treatment?

Answer 25

- kills disease-causing microorganisms - prevents growth of algae and prevents bad tastes and smells - Removes discoloration caused by organic compounds.

Question 26

How is chlorine used in water treatment?

Answer 26

Chlorine is added to water in dilute concentrations. - The HClO reacts with bacteria in water - Position of equilibrium moves to the right to replace the HClO that`s reacted - SO when HClO has done it`s job there is little Cl left in the water.