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Chemistry A Level 1 > group 7 > Flashcards

group 7 Flashcards

1
Q

what is the trend in bpt down group 7

A

increases down the group

because size of 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

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 and why not HCl when testing for halide ions

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 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 precipitate
Ag+ + I- –> AgI (s)

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8
Q

what happens when AgCl- precipitate when dilute/conc NH3 are added

A

AgCl- dissolves in both dilute and conc

AgCl (s) + 2NH3 (aq) –> [Ag(NH)2)]+ (aq) + Cl-

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9
Q

what happens when AgBr- precipitate when dilute/conc NH3 are added

A

only dissolve in conc

AgBr (s) + 2NH3 (aq) –> [Ag(NH3)2]+ (aq) + Br-

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10
Q

what happens when AgI- precipitate when dilute/conc NH3 are added

A

will not dissolve in either

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11
Q

what is the trend in oxidising ability down group 7

A

decreases down group
Cl best, I worst

Cl has fewest 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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12
Q

equation for Cl2 oxidising 2I-

A

Cl2 + 2I- –> 2Cl- + I2

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13
Q

what is the trend in reducing ability of the halides down the group

A

increases down the group
Cl- worst and 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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14
Q

H2SO4 + 2I- –> ?

A

SO4 2- + 2Hi

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15
Q

H2SO4 + 2H+ + 2I- –> ?

A

SO2 + I2 + 2H2O

SO2 is a choking gas with a pungent odor

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16
Q

H2SO4 + 6H+ + 6I- –> ?

A

S + 3I2 + 4H2O

S is a yellow solid

17
Q

H2SO4 + 8H+ + 8I- –> ?

A

H2S + 4I2 + 4H2O

H2S smells of rotten eggs

18
Q

products of Br- + H2SO4

A

HBr and SO2

19
Q

does Cl- reduce H2SO4

A

no, not powerful enough reducing agent; only HCl is formed

20
Q

why is adding chlorine to drinking water ? is it safe ?

A

forms ClO- ions which oxidise all microorganisms in water

once it has done its job, little remains, and the health benefits outweigh the risks

21
Q

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

22
Q

why is ozone not used to purify water in the UK

A

more expensive than chlorine, evaporates from water more quickly

23
Q

what is the equaton for the reaction of Cl2 with water

A

Cl2 (g) + H2O (l) –> HClO (aq) + HCl (aq)

24
Q

what type of reaction of chlorine with water

A

disproportionation; chlorine is both oxidised and reduced

25
Q

what are the two forms of the chlorate ion

A

ClO- is chlorate (I)
ClO3- is chlorate (V)

26
Q

what is the equation for making bleach

A

Cl2 + 2NaOH –> NaCl + NaClO + H2O

NaClO is bleach

27
Q

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

A

2Cl2 + 2H2O –> 4HCl + O2 (g)

28
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

Chemistry A Level 1 (19 decks)

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