Inorganic 1: Group 7 Flashcards

1
Q

what is the trend in bpt down group 7?

A

increases down the group because the size of the atom increases as more occupied electron shells –> stronger vdw 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?

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 CO3^2-

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 of 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 (and 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) + Cl-
  • AgI- will not dissolve in either
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9
Q

what is the trend in oxidising ability down the group?

A

decreases down the group (Cl best, I worst)
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 an equation for Cls 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?

A

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

all equations

A

H₂SO₄ + 2I^- → SO₄^2- + 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