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Chemistry > Developing metals > Flashcards

Developing metals Flashcards

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1
Q

What is oxidation?

A

A loss of electrons

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2
Q

What is reduction?

A

A gain of electrons

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3
Q

What is a reducing agent?

A

Donates electrons

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4
Q

What is an oxidising agent?

A

Takes/accepts electrons

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5
Q

Does an oxidising agent lose or gain electrons during a redox reaction?

A

Gain

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6
Q

Does a reducing agent lose or gain electrons during a redox reaction?

A

lose

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7
Q

Apart from multiplying up the reactants and products, name three things you can add to balance a half equation.

A

H+ ions
Electrons
Water

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8
Q

What are acid base titrations used for?

A

To find how much acid is needed to neutralise a base

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9
Q

In an acid base titration what goes into the burette?

A

The acid

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10
Q

What is the purpose of a redox titration?

A

How much oxidising agent is needed to react with a quantity of reducing agent

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11
Q

What is a common oxidising agent used in redox titrations?

A

manganate(VII) ions

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12
Q

How do you do a redox titration?

A

1) Measure quantity of reducing agent using pipette and put in conical flask
2) Add dilute sulfuric acid in excess to conical flask
3) Add oxidising agent to the burette
4) Swirl the conical flask as you add it
5) Stop when you reach end point
6) repeat until concordant titrations

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13
Q

In a redox reaction what goes in the burette?

A

The oxidising agent

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14
Q

Why do you add dilute sulfuric acid to the conical flask in a redox titration?

A

The acid is added to make sure there are plenty of H+ to allow the oxidising agent to be reduced

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15
Q

What is the colour change in a redox reaction using potassium manganate(VII)?

A

colourless –> pink end point

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16
Q

What are the reactions in an electrochemical cell?

A

oxidation and reduction

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17
Q

What reaction happens at the anode in an electrochemical cell?

A

oxidation

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18
Q

What reaction happens at the cathode in an electrochemical cell?

A

reduction

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19
Q

What does an electrochemical cell consist of?

A

two different metals dipped in salt solutions of their own ion and connected by a wire and a salt bridge

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20
Q

What direction do electrons flow through a wire in an electrochemical cell?

A

from the most reactive metal to the least reactive metal

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21
Q

What is cell potential?

A

The voltage between the two half-cells

EMF Ecell

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22
Q

What electrode do you need when the half cell consists of two aqueous solutions of the same element?

A

Needs to conduct electricity but be very inert

eg.platinum or graphite

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23
Q

How do you set up an electrochemical cell?

A

1) Clean surface of strip of metals you’re using as electrodes with sand paper
2) Clean electrodes using propanone
3) Place electrode into beaker filled with solution containing ions of that metal
4) Create a salt bridge by dipping a piece of filter paper in salt solution and then drape it between the two beakers
5) connect electrodes with voltmeter crocodile clips and wires

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24
Q

Does the reaction go forwards at the half cell if the electrode potential is more or less positive?

A

more positive

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25
Q

What happens at the half cell with a more negative electrode potential?

A

it is oxidised so goes backwards

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26
Q

What are standard conditions for electrode potentials?

A

298K
100kPa
1.00 moldm^-3

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27
Q

What are electrode potential measured against?

A

Stand hydrogen electrodes

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28
Q

What is standard electrode potential?

A

Voltage of half cell measured under standard conditions when half cell is connected to a standard hydrogen potential

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29
Q

What is the equation for Ecell?

A

Ecell = (E more positive) - (E more negative)

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30
Q

Do more reactive metals have more negative or positive electrode potentials?

A

more negative

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31
Q

Why do more reactive metals have more negative electrode potentials?

A

more likely to lose electrons to form a positive ion

32
Q

Do less reactive metals have more negative or positive electrode potentials?

A

more positive

33
Q

Why do less reactive metals have more positive electrode potentials?

A

more likely to gain electrons to form a negative ion

34
Q

How can you tell if a reaction is feasible, at standard conditions, using electrode potentials?

A

Use them to calculate Ecell

if Ecell is positive it is feasible if it is negative it is not

35
Q

What is the voltage of the standard hydrogen electrode half-cell?

A

0.00V

36
Q

Why is rust less likely under alkaline conditions?

A

OH- ions added means
2(H2O) + O2 +4e- –> 4OH-
is shifted to left to so more electrons produced so
Fe2+ + 2e- –> Fe
Shifts to the right to balance this so less Fe2+ to form Fe(OH)2

37
Q

What are the half equations in the start of rusting of Fe?

A

Fe2+ + 2e- –> Fe

2(H2O) + O2 +4e- –> 4OH-

38
Q

What equations show how Fe2+ react to make Fe(OH)3 in the process of rusting?

A

Fe2+ +2OH- –> Fe(OH)2

2(H2O) + O2 + 4Fe(OH)2 –> Fe(OH)3

39
Q

What is rust?

A

Fe2O3 xH2O

40
Q

What was rust before it became hydrated iron(III) oxide?

A

iron(III) hydroxide

Fe(OH)3

41
Q

How do you prevent rusting?

A

Barrier

Sacrificial metal

42
Q

What are two examples of the barrier method of rust prevention?

A
  • Coating with a polymer (Painting)

- Oiling or greasing

43
Q

When would you use oiling or greasing to prevent rust?

A

When moving parts are involved

44
Q

What is the sacrificial method?

A

Placing a more reactive metal with the iron so the water and oxygen react with that metal instead

45
Q

What sacrificial metal is most often used? Why?

A

Zinc

It has a more negative electrode potential than Fe so it will be oxidised instead

46
Q

What is galvanising?

A

Coating something zinc

47
Q

What two substances react with iron to produce rust?

A

Water and Oxygen

48
Q

What is a complex ion?

A

A central metal ion surrounded by datively bonded ligands

49
Q

What is a dative covalent bond?

A

Both shared electrons come from the same atom

50
Q

In a complex where do the shared pair of electrons in the dative bond come from?

A

The ligands

51
Q

What is a ligand?

A

Something that donates a pair of electrons to a central transition metal ion to form a dative bond

52
Q

What is a monodentate ligand?

A

Has one lone pair of electrons

53
Q

What is a bidentate ligand?

A

Has two lone pairs of electrons

54
Q

What is a polydentate ligand?

A

Has multiple lone pairs of electrons

55
Q

What is are four examples of monodentate ligands?

A

H2O
NH3
CN-
halide ions

56
Q

What is an example of a bidentate ligand?

A

ethanedioate

57
Q

What is the coordination number?

A

The number of dative bonds formed with ligand

58
Q

What shape would a molecule with a coordination number of 6?

A

Octahedral

59
Q

What two shapes would a molecule with coordination number of 4 have?

A

Tetrahedral

Square planar

60
Q

What size bond angles does an octahedral complex have?

A

90 degrees

61
Q

What size bond angle does a tetrahedral shape have?

A

109.5 degrees

62
Q

What size bond angle does a square planar shape have?

A

90 degrees

63
Q

How do ligands affect the 3d sub-shell of transition metal ions?

A

Split it into two energy levels because some orbitals gain energy

64
Q

When will the compound look colourless or white? why?

A

If the 3d sub shell is full or empty

because the electrons won’t jump up to higher orbitals

65
Q

What do you mix with aqueous transition metal ions for them to become coloured?

A

NaOH or NH3 to make a coloured hydroxide precipitate

66
Q

What is ligand substitution? what does it cause?

A

One ligand being swapped for another

a colour change

67
Q

Why do transition metal compounds make good catalysts

A

They can change oxidation states by gaining or losing electrons in their D orbitals so they can transfer electrons to speed up reactions

68
Q

Why can transition metal compounds cause health risks?

A

Their compounds can be toxic

69
Q

Stages of heterogeneous catalysis

A
  1. Adsorption
  2. Bonds in molecule break
  3. New bonds form
  4. desorption
70
Q

What makes a good heterogeneous catalyst?

A

Attract the reactant strong enough so it is held to the surface long enough to bond but not too strong it won’t desorb

71
Q

What is a heterogeneous catalyst?

A

A catalyst in a different state to the reactants

72
Q

What is a homogeneous catalyst?

A

A catalyst in the same state as the reactant

73
Q

How does a homogeneous catalyst work?

A

Combine with reactants to form intermediate species which then reacts to form products and reform the catalyst

74
Q

What happens to white light that makes a transition metal ion colour?

A

One frequency of light is absorbed

the rest are transmitted (the colour you see)

75
Q

How do you set up a colorimeter?

A
  1. Pick a filter that is a colour that’s absorbed
  2. Set zero using a blank sample
  3. Place sample in a cuvette and measure
76
Q

What does a high absorbance on the colorimeter mean?

A

Very concentrated

77
Q

What is monochromatic light?

A

light of a single colour

Chemistry (8 decks)

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