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chemistry > ES bdefghijk: Properties of the halogens; oxidation states; redox > Flashcards

ES bdefghijk: Properties of the halogens; oxidation states; redox Flashcards

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1
Q

The halogens are the most reactive non-metal group; none are found in elemental form.

State the trends in the following properties of the halogens, going down the group:

  • Reactivity/electronegativity
  • Colour
  • Melting/boiling point
A
  • Reactivity/electronegativity decreases
  • Colours darken
  • Melting/boiling points increase (volatility decreases)
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2
Q

Which type of intermolecular bonding occurs between halogen molecules?

A

Instantaneous dipole-induced dipole interactions.

Otherwise known as dispersion or London forces (named after German physicist Fritz London)

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3
Q

Why do the melting/boiling points of the halogens increase down the group?

A
  • More electrons per molecule
  • Stronger instantaneous dipole-induced dipole intermolecular forces
  • Require more energy to overcome
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4
Q

Why is fluorine more reactive than chlorine?

A
  • Outer shell closer to nucleus (less sheilding)
  • Electrostatic attraction stronger
  • Accepts an electron more readily to fill its outer shell
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5
Q

What are the colours and physical states at room temperature of each diatomic compound?

  • fluorine
  • chlorine
  • bromine
  • iodine
A
  • Fluorine: yellow gas
  • Chlorine: green gas
  • Bromine: red liquid (volatile)
  • Iodine: grey solid (sublimes to purple vapour)
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6
Q

What colour is gaseous bromine?

A

Red-brown.

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7
Q

How do the halogens behave when added to water?

A
  • Fluorine reacts with water
  • Others are sparingly soluble (more so in organic solvents)
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8
Q

What are the colours of solutions of the following halogens in water?

  • Chlorine
  • Bromine
  • Iodine
A
  • Chlorine = pale green
  • Bromine = orange-brown
  • Iodine = brown

Trend down group is colours darkening; same here.

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9
Q

What are the colours of solutions of the following halogens in cyclohexane?

  • Chlorine
  • Bromine
  • Iodine
A
  • Chlorine = pale green
  • Bromine = orange-brown
  • Iodine = violet

Trend down group is colours darkening; same here.

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10
Q

When cyclohexane is added to aqueous solutions of halogens, which solvent forms the upper layer?

A

Cyclohexane upper layer

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11
Q

What would you add to a halide solution to precipitate it?

A

Solution of silver ions, typically silver nitrate (AgNO3)

Ag+ + X- → AgX

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12
Q

What are the colours of the silver halides:

  • Silver chloride
  • Silver bromide
  • Silver iodide?
A
  • Silver chloride = white
  • Silver bromide = cream
  • Silver iodide = yellow

Trend down group is colours darkening; same here.

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13
Q

What are the appearances of the following silver halides in ammonia?

  • Silver chloride
  • Silver bromide
  • Silver iodide
A
  • Silver chloride = colourless (completely dissolved)
  • Silver bromide = cloudy (partially dissolved)
  • Silver iodide = opaque (insoluble precipitate)
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14
Q

How is bromine extracted from dissolved bromide ions in the lab?

A

Cl2 solution added to Br- solution + displaces bromine.

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15
Q

In one method of manufacturing bromine from sea water:

  1. Cl2 is bubbled through sea water to produce Br2
  2. Steam is blown through to produce Br2 vapour
  3. Vapour is mixed w/ SO2 + passed into water
  4. Steam + Cl2 are blown through to release Br2 from HBr
  5. Br2 is dried using conc. H2SO4
  • ​Which property of the halogens do steps 1 and 4 illustrate?
  • Suggest why it is necessary to produce bromine in 1 and again in 4
A
  • Chlorine is a better oxidising agent than bromine so displaces it
  • Br2 produced in step 1 is too dilute
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16
Q

In one method of manufacturing bromine from sea water:

  1. Cl2 is bubbled through sea water to produce Br2
  2. Steam is blown through to produce Br2 vapour
  3. Vapours are condensed - 2 layers form
  4. Dense Br2 layer is run off from H2O layer
  5. Impure Br2 is distilled + dried
  • ​Explain why 2 layers form in step 3
  • State and explain which is the upper layer in step 4
A
  • Bromine has a low solubility in water
  • H2O is upper layer since bromine is denser
17
Q

Which properties of bromine make it possible to separate it from:

  • Water
  • Chlorine?
A
  • Sparingly soluble in water, so higher density bromine layer forms. Can be run off from water, which floats on top
  • Different melting points, so can be separated by distillation
18
Q

Typical oxidation state of aluminium

A

+3

19
Q

When is oxygen’s oxidation state not -2?

A
  • When combined with F
  • When in peroxide, H2O2
20
Q

When are the halogens’ oxidation states not -1?

A
  • Cl: combined with O / F
  • Br: combined with O / F / Cl
  • I: combined with O / F / Cl / Br
21
Q

When is hydrogen’s oxidation state not +1?

A

When in metal hydrides, e.g. NaH

22
Q

Name the 2 ions:

  • CrO42-
  • VO3-
A
  • Chromate(VI)
  • Vanadate(V)
23
Q

Both of the following chlorates have charge 1-. Write the formula for them.

  • Potassium chlorate(III)
  • Sodium chlorate(V)
A
  • KClO2-
  • NaClO3-
24
Q

Give the systematic name of:

  • HClO
  • KIO3
A
  • Chloric(I) acid
  • Potassium iodate(V)
25
Q

Write the balanced equation for the following reaction:

H+ + I- + H2SO4 → H2S + H2O + I2

A

Balance ox states:

H+ + I- + H2SO4 → H2S + H2O + I2

H: remains +1

I: -1 → 0 (loses 1 e-)

S: +6 → -2 (gains 8 e-)

O: remains -2

H+ + 8I- + H2SO4 → H2S + H2O + 4I2

1 H2SO4 gains e- from 8 I-, forming 4 I2 and 1 H2S.

Balance rest: (what isn’t involved in redox)

8H+ + 8I- + H2SO4 → H2S + 4H2O + 4I2

26
Q

Write the balanced equation for the following reaction:

Br- + H+ + H2SO4 → Br2 + SO2 + H2O

A

Balance ox states:

Br- + H+ + H2SO4 → Br2 + SO2 + H2O

Br: -1 → 0 (loses 1 e-)

H: remains +1

S: +6 → +4 (gains 2 e-)

O: remains -2

2Br- + H+ + H2SO4 → Br2 + SO2 + H2O

Balance charge + rest: (what isn’t involved in redox)

2Br- + 2H+ + H2SO4 → Br2 + SO2 + 2H2O

27
Q

Balance and complete this equation:

Br2 + SO2 + 2H2O → HBr + ___

A

Br2 + SO2 + 2H2O → HBr + ___

Balance ratio:

Br2 + SO2 + 2H2O → 2HBr + ___

Deduce other product:

4 oxygens, 2 Hs + 1 S unaccounted for:

Br2 + SO2 + 2H2O → 2HBr + H2SO4

(Optional) Check with ox states:

Ox state of S in H2SO4 = +6

Br: 0 → -1 (so Br2 gains 2 e-)

S is only species which can be oxidised (constant ox states of O + H)

S: +4 → +6 QED

chemistry (50 decks)

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