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

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

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1
Q

Oxidation

A
  • Loss of electrons
  • Gain of oxygen
  • Loss of hydrogen
  • Increase in oxidation state
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2
Q

Reduction

A
  • Gain of electrons
  • Loss of oxygen
  • Gain of hydrogen
  • Decrease in oxidation state
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3
Q

Oxidation state

A

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.

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4
Q

Trends in electronegativity down group 7

A

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

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5
Q

Trends in boiling point down group 7

A

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.

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6
Q

Trends in oxidizing abilities down group 7

A

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

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7
Q

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

A

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

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8
Q

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

A

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

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9
Q

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

A

No reactions

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10
Q

Trend in reducing abilities down group 7

A

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.

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11
Q

Reactions of solid sodium halides with conc. H2SO4

A

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

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12
Q

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

A

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

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13
Q

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

A

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

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14
Q

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)

A

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)

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15
Q

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)

A

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

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16
Q

Method for testing for halide ions

A

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

17
Q

Why is dilute nitric acid added?

A

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

18
Q

Testing for chloride ions (Cl-)

A

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

19
Q

Testing for Bromide ions (Br-)

A

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

20
Q

Testing for Iodide ions (I-)

A

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

21
Q

Reaction of chlorine with cold, dilute aqueous NaOH

A

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

22
Q

Uses of Chlorate ion

A

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

23
Q

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

A

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

24
Q

Reaction of chlorine and water to form chloride ions and oxygen

A

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.

25
Q

Benefits of why chlorine used in water treatment?

A
  • kills disease-causing microorganisms
  • prevents growth of algae and prevents bad tastes and smells
  • Removes discoloration caused by organic compounds.
26
Q

How is chlorine used in water treatment?

A

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 thats reacted - SO when HClO has done its job there is little Cl left in the water.

Chemistry (12 decks)

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