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Chemistry > Oxidation and reduction. 2 > Flashcards

Oxidation and reduction. 2 Flashcards

1
Q

Define oxidation in terms of electron transfer

A

Oxidation is the loss of electrons

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2
Q

define reduction in terms of electron transfer

A

Reduction is the gaining of electrons

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3
Q

if a substance loses electrons, it is …..

A

oxidised

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4
Q

if a substance gains electrons, it is …

A

reduced

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5
Q

what are redox reactions

A

one substance is oxidised and one substance is reduced simutaneously (one cannot occour without the other)

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6
Q

what is an oxidising agent/ reagent

A

a substance that causes oxidation in another substance
(It itself is reduced)

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7
Q

what is a reducting agent

A

substance that causes reduction in another substance
(itself is oxidised)

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8
Q

Give an example of an oxidising agent used in swimming pools

A

Chlorine is added to swimming pools to disinfect them

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9
Q

Explain how oxidising agent s and reducting agents are used in different bleaches

A

Oxidising agent Sodium hypocloride in household bleaches
Reducing agentsulfur dioxide is used to bleach wood

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10
Q

Define oxidation number

A

the charge an atom has or appears to have when electrons are distributed according to certain rules

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11
Q

In any neutral compound/molecule the sum of the oxidation numbers must equal…

A

0

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12
Q

In any complex ion, the sum of all the oxidation numbers must equal…

A

The charge of the ion

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13
Q

A free element (Diatomic element) (An element not bonded to another element or bonded to itself) always has an oxidation number of….

A

0

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14
Q

The oxidation number of an simple ion is equal to…

A

the charge of the ion

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15
Q

Oxygen 99% of the time has a oxidation number of…

A

-2 in its compounds

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16
Q

Hydrogen 99% of the time has an oxidation number of…

A

+1 in its compounds

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17
Q

Fluorine always has an oxidation number of..

A

-1 in its compounds

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18
Q

Group 1 elements always have an oxidation number of …and
Group 2 elements always have an oxidation number of…

A

+1
+2

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19
Q

When is Oxygens number not -2, And explain why

A

In peroxides ( Bonded w/ H) where its -1 as oxygen is more electronegative (H2O2)

In Oxygen difluoride OF2 (+2) F is more electronegative element

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20
Q

When is hydrogen oxidation not +1

A

In a metal hydride where it has an oxidation number of -1
hydrodengen is more electronegative than the metal

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21
Q

Define oxidation in terms of change in oxidation number

A

Oxidation is a increase in oxidation number

22
Q

define reduction in terms of a change in oxidation number

A

reduction is a decrease in oxidation number

23
Q

How does the oxidation number of the oxidising agent change during a redox reaction

A

decreases

24
Q

how does the oxidation number of the reducting agent change during a redox reaction

A

increases

25
Q

what is the electrochemical series

A

series of metals arranged in order of how esliry they lose electrons

26
Q

what does a metal higher in the electrochemical series do to one lower in the series

A

will reduce a metal lower down and displace it from a compound

27
Q

Name the metals in decending order from most to least reactive

A

postassim
Sodium
Calcium
Magnesium
Alminium
Zinc
Iron
Lead
Hydrogen
Copper
Silver
Gold

28
Q

Writea balanced equation for the reaction that occours when magnesium is placed in copper II sulfate solution. Explain this reaction and describe what is observed

A

Magnesium is higher than copper in the electrochemical series. Mg reduces copper and desplaces copper from the compound

Blue colour of copper II sulfate becomes colourless
Brown precipate of copper metal forms

29
Q

What is observed when copper is placed in dilute sulfuriic acid, explain

A

copper is lower than hydrogen in the electrochemical series and will not reduce and displace it from a compound

30
Q

Give an application of knowledge of the electrochemical series

A

iron is used to reduce and dispace less reactive metal such as copper
copper is useful in electronic industury (wires)

31
Q

Which metals from the electrochemical series are found free in nature? and why?

A

Lead, sopper, silver, Gold.
These metals are at the bottom of the electrochemical sries and are very unreactive

32
Q

Describe the procedure and name the result/observation

To study halogens as oxidising agents
chlorine to oxidise bromine ions Br- to Br2

A

add some chlorine water to a potassium bromide solution
The solution turns red due to the formation of bromine Br2

33
Q

write two half equations describing the reaction

To study halogens as oxidising agents
chlorine to oxidise bromine ions Br- to Br2

A

Oxidation 2Br- - 2e- –> Br2
Reduction C2 + 2e- –> 2Cl-

34
Q

State your conclusion as a result of this expeirment

To study halogens as oxidising agents
chlorine to oxidise bromine ions Br- to Br2

A

Chlorine has a higher ocidising ability than bromine and will oxdise bromine

35
Q

state the procedure and the obervation/ result

To study halogens as oxidising agents
Using chlorine to oxidise iodide ions to iodine I- to I2

A

Add clorine water to postassium iodine
The solution turns red-brown due to the formation of Iodine.

36
Q

state two half reactions that describe the reaction

To study halogens as oxidising agents
Using chlorine to oxidise iodide ions to iodine I- to I2

A

Oxidation 2I- - 2E- –> 2Cl-
Reduction Cl2 + 2e- —> 2Cl-

37
Q

describe the conclusion from this expeirment

To study halogens as oxidising agents
Using chlorine to oxidise iodide ions to iodine I- to I2

A

Chlorine has a higher oxidising ability than iodine

38
Q

Why are halogens good oxidising agents

A

they have high electronegativity values

39
Q

Why does the reactivity/ oxidising ability of the halogens decrease going down the group

A

atomic radius increases going down the group, no increase in effective nuclear charge

40
Q

describe the procedure and the result/observation

Using a halogen to oxidise Fe2+ ions to Fe3+ ions

A

add cl water to iron sulfate solution.
Add dilute sodium hydroxide solution to bring Fe3+ ions out of solution.
Result: A green-brown precipate conforms the presence of Fe3+ ions

41
Q

Write two half equations of describing this reaction

Using a halogen to oxidise Fe2+ ions to Fe3+ ions

A

Oxidation 2Fe2+ - 2e- –> 2Fe3+
reduction Cl2 + 2e –> 2Cl-

42
Q

Describe the conclusion

Using a halogen to oxidise Fe2+ ions to Fe3+ ions

A

clorine / bromine/ iodine is the oxdising agent

43
Q

Describe the result / observation

Use halogens to oxidise sulfite ions (SO3 2-) to sulfate ions (SO4 2-)

A

Add barium chloride: a white percipate forms.
Add HCL
If the white percipate dissolves the ions are sulfite (so3 2-)
If the white percipate remains the ions are suldate (SO4 2-)

44
Q

writw two balanced equations to describe this expeirment

Use halogens to oxidise sulfite ions (SO3 2-) to sulfate ions (SO4 2-)

A

Oxidation SO3 2- + H2O –> So4 2- + 2H+
Reduction Br2 + 2e- –> 2Br -

45
Q

Describe the conclusion

Use halogens to oxidise sulfite ions (SO3 2-) to sulfate ions (SO4 2-)

A

the halogens are the oxidising agent

46
Q

Describe the procedure and the result/obervation

Displacement reactions of metals
copper vs Zinc

A

Add zinc powder to copper II sulfate.A brown precipitate of copper metal forms.
The blue solution of the copper suldate soltuions slowly become colourless

47
Q

Write two half equations to describe this expeirment

Copper vs Zinc displacement reaction of metals

A

Zn - 2e- —> Zn2+
Cu2+ + 2e —> Cu↓

48
Q

describe the procedure and the result/ obervation of this reaction

copper vs mg displacement reaction

A

add magnesium ribbon to a copper II Sulfate soltuion
Result/ Observation A brown precipation of copper metals forms.
The blue colour of copper sulfate solution rapidly becomes colourless

49
Q

Write two half equations to describe this reaction

Displacement reactions of metals
copper vs mg

A

Mg - 2e- –> Mg2+
Cu 2+ +2e- –> Cu↓

50
Q

Describe any difference in what was observed between adding the zinc to a copper (II) solution
and adding the magnesium to a copper (II) solution, and explain why this is the case in terms of
relative reducing abilities of:
a) Zinc metal and copper metal
b) Magnesium metal and copper metal

A

The blue colour of copper (II) sulfate decolourises more rapidly/ to a greater degree when megnesium is added than when zinc is added
a) zinc is higher than copper in the electrochemical sries and has a higher reducing ability. zinc is only slightly higher than copper so reaction occours slowly.
b) mg is higher than copper in electrochemica series (higher reducting bility) Mg is much higher i=than copper in electrochemical series, this occour more rapidly

Chemistry (30 decks)

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