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Chemistry Unit 2 > Redox and Halides > Flashcards

Redox and Halides Flashcards

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0
Q

Define oxidation state

A

How many electrons are lost or gained from being an atom

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1
Q

Define disproportionation reaction

A

Describes a reaction when one element is simultaneously oxidised and reduced in the same reaction
The same element appears twice in the products

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2
Q

What are the oxidation states of oxygen in compounds?

A 
Usually -2
If in a peroxide, H2O2, it is -1
OF2 is +2
O2F2 is +1
O2 is 0
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3
Q

What is the oxidation state value of every element

A

Zero

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4
Q

What are Hydrogens oxidation states

A

Usually +1
When with a metal it is -1
When H2 it is 0

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5
Q

When is chlorides oxidation state positive

A

When with a negative oxygen

It is usually -1

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6
Q

What is a reducing agent

A

An electron donor

The substance being oxidised

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7
Q

What is an oxidising agent

A

An electron acceptor

The substance being reduced

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8
Q

If a substance in oxidised, how does it charge change?

A

It gets more positive as electrons are lost

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9
Q

If a substance is reduced, how does its charge change

A

It gets more negative as electrons are gained

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10
Q

What are the five steps when writing full half equations?

A 
Calculate oxidation states
Balance the element
Sort the electrons
Balance the oxygen using H2O
Balance the hydrogen using H+ ions
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11
Q

If you are told it is an acidic solution, what must the half equation contain?

A

H+ ions

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12
Q

What are halogens

A

Soluble salts
Highly reactive
Non metals
Group 7 elements

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13
Q

State the halogens and their properties

A

Fluorine: pale yellow gas
Chlorine: green yellow gas
Bromine: red/brown liquid
Iodine: black solid

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14
Q

Give more detailed properties of iodine

A

When heated to vapour, it is purple
Does not dissolve in water but makes a brown solution with aqueous potassium iodide
Will dissolve in a non-polar solvent
Iodine turns blue/black with starch

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15
Q

State the trend in boiling point of the halogens

A

Increases down the group

Increasing strength van der Waals as size and relative mass of each atom increases

16
Q

State the trend in electronegativity of the halogens

A

Decreases down the group
All highly electronegative
Larger atoms attract shared electrons less than smaller ones (as atoms increase in size, electronegativity decreases)

17
Q

Which halogen is the strongest oxidising agent

A

Fluorine

Higher up the group, less shielding, smaller, more easily attracts electrons

18
Q

What are the general steps and observation when testing for Cl, Br and I ions

A

1) acidify with HNO3: reacts with impurities I.e. Carbonates which may cause false positive, cannot use HCl as it contains chloride ions
2) add AgNO3: forms a precipitate, Cl is white, Br is cream and I is yellow
3) add dilute ammonia: AgCl redissolves, no change in others
4) add conc ammonia: AgCl and AgBr redissolve, not change in AgI

19
Q

What are the general steps and observations when testing for F ions

A

When HNO3 and AgNO3 are added, it forms a colourless solution as AgF is soluble in water

20
Q

How do you test for sulphate ions

A

Add HNO3
Add BaCl2
White precipitate BaSO4 forms
Ba+2 + SO4-2 = BaSO4

21
Q

What happens when a halide ions reduces another substance and what is the half equation for this reaction?

A

The halide oxidised to a halogen

2X- = X2 +2e-

22
Q

When a halide is used to reduce a substance, what are the reagents that are usually used to react with conc sulphuric acid

A

Sodium chloride, sodium bromide, sodium iodide

Some halide ions are strong enough reducing agents to reduce sulphuric acid to water and sulphur along with the halogen

23
Q

Which halides reduces sulphuric acid and to what?

A

Cl does not reduce it
Br reduces it from S(+6) to S(+4)
I reduces it from S(+6) to S(-2)

24
Q

What is the strongest reducing agent

A

Iodine
As go down group, attraction between nucleus and outer electron gets weaker as ion gets bigger - electrons further away and greater shielding

25
Q

Discuss the reaction of NaF or NaCl with sulphuric acid

A

NaX + H2SO4 = NaHSO4 + HX
HCl produces steamy fumes as gas comes into contact with moisture in the air
HF and HCl are not strong enough reducing agents to reduce sulphuric acid further
Not redox reactions as oxidation state of halide (-1) and sulphur (+6) remain the same

26
Q

Discuss the reaction of NaBr with sulphuric acid

A

NaBr + H2SO4 = NaHSO4 + HBr
Steamy fumes if HBr - stronger reducing agent and reacts with sulphuric acid in redox reaction

2HBr + H2SO4 = Br2 + SO2 + 2H2O
Sulphur is reduced
Br is oxidised

Produces choking colourless fumes of SO2 and brown/orange fumes of Br2

27
Q

Discuss the reaction of NaI with sulphuric acid

A

NaI + H2SO4 = NaHSO4 + HI
2HI + H2SO4 = I2 + SO2 + 2H2O
Sulphur is reduced and iodine oxidised

6HI + SO2 = H2S + 3I2 + 2H2O
H2S is toxic and forms a gas that smells is bad eggs

28
Q

When will a halogen displace a halide

A

A halogen will displace a halide from a solution if the halide is below it in the periodic table

29
Q

How do you know is a displacement reaction has occurred

A

A colour change is seen when adding a few drops of an aqueous halogen to a solution containing halide ions

30
Q

Which halogens displace which halides

A

None of the halogens displace potassium chloride solution
Chlorine water displaces KBr to form an orange solution and Br2 and displaces KI to form a brown solution and I2
Bromine water displaces KI to form a brown solution and I2
Iodine solution does not displace any of the halide solutions

31
Q

How is bleach made

A

2NaOH + Cl2 = NaClO + NaCl + H2O
At room temp
NaClO is bleach
Chlorine is both oxidised and reduced - disproportionation

32
Q

What is the reaction between chlorine and cold water and how does the product HClO go onto further react

A

Cl2 + H2O = HCl + HClO (chloric acid)

HClO + H2O = ClO- + H3O+

33
Q

How does chlorine react with water under UV light

A

2Cl2 + 2H2O = 4HCl + O2

34
Q

Why is chlorine used to treat water

A

Chloric acid is a powerful disinfectant that kills bacteria

Chemistry Unit 2 (7 decks)

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