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Chemistry > Group 7 Halogens and REDOX > Flashcards

Group 7 Halogens and REDOX Flashcards

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1
Q

Oxidising agent

A

Electron acceptor

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2
Q

Reducing agent

A

Electron donor

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3
Q

State the equation for the reaction between chlorine and cold water and explain what type of reaction it is

A 
Cl2 + H2O -> HClO + HCl
Disproportionation reaction (Cl is oxidised and reduced)
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4
Q

Describe displacement reactions between halogens and halide ions

A 
Reactivity decreases down Group 7
Cl2 displaces Br-
- orange-brown solution 
Cl2 displaces I- 
- brown solution-black solid 
Br2 displaces I-
- dark brown solution-black solid (NEVER GREY SOLUTION)

sodium halide reacts with element in test (NOT ion with NaX)

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5
Q

Name products iodide ions can reduce sulphuric acid into (give oxidation state of sulphur in each) and suggest observations

A

SO2 (+4) - pungent / choking gas
S (0) - yellow solid
H2S (-2) - smell of bad eggs

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6
Q

Suggest why pool water can become more acidic than usual on a hot day and give an equation to support your reason

A

Pool water contains chlorine which reacts with water to produce HClO (chloric I acid) - disinfectant that kills bacteria
In the presence of sunlight chloric I acid decomposes to form even more HCl
2Cl2 + 2H2O -> 4HCl + O2

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7
Q

Give an example of a reagent that can be used to show that the reducing ability of bromide ions is different to chloride ions

A

CONCENTRATED H2SO4

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8
Q

Give equations for the reactions between chlorine and cold sodium hydroxide and suggest uses of the resulting solution

A

Cl2 + 2NaOH -> NaCl + NaClO + H2O
NOT Cl2 + NaOH -> NaClO + HCl since hydrochloric acid is neutralised by NaOH

NaClO = bleach/disinfectant

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9
Q

Suggest why fluoride ions cannot be tested for using silver nitrate

A

Silver fluoride is soluble so no precipitate

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10
Q

Test for halides using concentrated sulphuric acid

A

F-/Cl- steamy acidic fumes (of HF/HCl)
Br- steamy acidic fumes (of HBr) and brown vapour (Br2)
I- steamy acidic fumes (of HI) and purple vapour (I2)

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11
Q

Identify additional gaseous products formed when potassium bromide/iodide react with concentrated sulphuric acid and state the type of reaction

A

HBr and HI in acid-base reaction

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12
Q

Explain the colour changes observed when universal indicator paper is dipped into chlorine water

A

Turns red due to H+ ions from HCl then white since it is bleached by HClO

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13
Q

Give equation for reaction between chlorine and hydroxide ions

A

Cl2 + 2OH- -> ClO- + Cl- + H2O

  1. write out ionic equation
  2. replace H+ with OH- on both sides
  3. cancel out excess water on both sides
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14
Q

Evaluate the use of chlorine in water treatment

A
  • kills bacteria
  • toxic in high quantities
  • eye irritation
  • may react with organic compounds to make harmful substances
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15
Q

Test for solid metal halides

A

nitric acid/ silver nitrate solution
Cl- - white precipitate
Br- - cream precipitate
I- - yellow precipitate

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16
Q

Suggest why nitric acid is added when testing for metal halides

A

Removes carbonate and hydroxide impurities which could react with silver

17
Q

Suggest why you cannot investigate fluorine in displacement reactions

A

Fluorine in aqueous solution reacts with water

18
Q

How to write half equations in alkaline conditions

A
  • first balance in acidic conditions
  • for each H+ add one OH- to both sides
  • cancel H20
19
Q

Describe reaction between sodium chloride and concentrated sulphuric acid

A

NaCl + H2SO4 -> HCl + NaHSO4
(not -> Na2SO4 + 2HCl since requires stronger base)
- steamy acidic fumes of HCl which turn blue litmus paper red

19
Q

Describe reaction between bromide ions and concentrated sulphuric acid

A 
2Br- -> Br2 + 2e- 
H2SO4 + 2H+ + 2e- -> SO2 + 2H2O
2Br- + H2SO4 + 2H+ -> Br2 + SO2 + 2H2O
- steamy acidic fumes of HBr
- brown vapour 
- pungent gas
19
Q

Describe reaction between iodide ions and concentrated sulphuric acid

A 
2I- -> I2 + 2e-
H2SO4 + 8H+ + 8e- -> H2S + 4H2O
8I- + H2SO4 + 8H+ -> 4I2 + H2S + 4H2O
- steamy acidic fumes of HI
- purple vapour / dark grey solid 
- rotten egg smell
20
Q

What is the oxidation state of O in H2O2

A

-1

21
Q

Give equation for reaction between NaBr and concentrated sulphuric acid

A

2NaBr + 3H2SO4 -> 2NaHSO4 + Br2 + 2H2O + SO2

memorise products and balance NaHSO4 formed for NaI as well

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