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A-Level Chemistry > Group 7 > Flashcards

Group 7 Flashcards

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1
Q

What is the trend in boiling point down group 7? Why?

A

Increases down the group

Because: size of atom increases as more occupied electron shells → stronger van der Waals forces of attraction between molecules, take more energy to break

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2
Q

What is the trend in electronegativity down group 7? Why?

A

Decreases

Because: more occupied electron shells → greater atomic radius and outer electrons are further from the positive charge of the nucleus → lower force of attraction between the nucleus and electron pair in the covalent bond

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3
Q

What do you use to test for halide ions?

A

Acidified AgNO3

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4
Q

Why do you add HNO3? Why not HCl?

A

To remove CO₃2-

Adding HCl would add Cl- ions, giving a false positive result

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5
Q

Result and equation for Cl- test?

A

white ppt

Ag+ + Cl- → AgCl (s)

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6
Q

What is the result and equation for the test for Br-?

A

Cream ppt
Ag+ + Br- → AgBr (s)

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7
Q

What is the result and equation for the test for I-?

A

Yellow ppt
Ag+ + I- → AgI (s)

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8
Q

What happens (+ equations) to each of the silver halide precipitates when dilute/conc NH3 are added?

A

AgCl- dissolves in both dilute and conc
AgCl (s) + 2NH₃ (aq) → [Ag(NH₃)₂]+ (aq) + Cl-

AgBr- only dissolves in conc
AgBr (s) + 2NH₃ (aq) → [Ag(NH₃)₂]+ (aq) + Br-

AgI- will not dissolve in either

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9
Q

What is the trend in oxidising ability down the group? Why?

A

Decreases down group (Cl best, I worst)

Because: Cl has fewest occupied electron shells, greatest force of attraction between outer electrons and nucleus, easiest to gain electrons and be reduced → best oxidising agent

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10
Q

Write the equation for Cl2 oxidising 2I-

A

Cl₂ + 2I- → 2Cl- + I₂

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11
Q

What is the trend in reducing ability of the halides down the group? Why?

A

Increases down the group (Cl- worst, I- best)

Because: I- has the most occupied electron shells, so outer electrons are further from the nucleus, weakest force of attraction between outer electrons and positive charge of nucleus → easiest to be oxidised and lose electrons → best reducing agent

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12
Q

What products are formed when I- reduces H2SO4?

Do equations for all 4.

A

H₂SO₄ + 2I- → SO₄2- + 2HI

H₂SO₄ + 2H+ + 2I- → SO₂ + I₂ + 2H₂O (SO2 is a choking gas with a pungent odour)

H₂SO₄ + 6H+ + 6I- → S + 3I₂ + 4H₂O (S is a yellow solid)

H₂SO₄ + 8H+ + 8I- → H₂S + 4I₂ + 4H₂O (H2S smells of bad/rotten eggs)

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13
Q

What are the products of Br- + H2SO4?

A

HBr and SO₂

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14
Q

Does Cl- reduce H2SO4?

A

No, not a powerful enough reducing agent; only HCl is formed

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15
Q

Why is chlorine added to drinking water? Why is it safe?

A

Forms ClO- ions which oxidise (kill) all
microorganisms in water.

Once it has done its job, little remains, and the health benefits outweigh the risks of using it

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16
Q

What are potential risks of adding chlorine to drinking water?

A

Chlorine is toxic and damages the respiratory system in large enough quantities; can form carcinogens with hydrocarbons

17
Q

Why is ozone not used to purify water in the UK?

A

More expensive than chlorine, evaporates from water more quickly

18
Q

What is the equation for the reaction of Cl2 with water?

A

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

19
Q

What type of reaction is the reaction of chlorine with water?

A

Disproportionation; chlorine is both oxidised and reduced

20
Q

What are the two forms of the chlorate ion?

A

ClO- is chlorate (I)

ClO₃- is chlorate (V)

21
Q

What is the equation for making bleach?

A

Cl₂ + 2NaOH → NaCl + NaClO + H₂O

NaClO is bleach

22
Q

Give the equation for the reaction of chlorine and water in the presence of sunlight

A

2Cl₂ + 2H₂O → 4HCl + O₂ (g)

23
Q

What is desalination?

A

Converts saltwater into clean, potable water Either by reverse osmosis (using a smart membrane) or by vacuum distillation at low pressure and low temperature

24
Q

What are the advantages and disadvantages of desalination?

A

Advantages - safe, clean, drinkable water produced in places where it might not otherwise be available

Disadvantages - uses lots of energy, reverse osmosis has low efficiency, can disturb marine ecosystems

A-Level Chemistry (16 decks)

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