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A2 Chemistry > Period 3 and Redox Equilibria > Flashcards

Period 3 and Redox Equilibria Flashcards

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1
Q

What are the period 3 elements?

A

Na, Mg, Al, Si, P, S, Cl, Ar

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2
Q

Why is sodium more reactive than magnesium?

A

Because it only needs to lose 1 electron against magnesium’s two - removal of fewer electrons takes less energy.

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3
Q

What is the reaction between sodium and water? What is observed when this reaction occurs?

A

2Na(s) + 2H2O(l) —-> 2NaOH(aq) + H2(g)

The sodium appears to be a molten ball, and effervescence.

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4
Q

What is the reaction between Mg and water? What are the characteristics of this reaction?

A

Mg(s)+ 2H2O(l) —-> Mg(OH)2(aq) + H2(g)

This is a slow reaction - it is faster with steam.

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5
Q

Why is NaOH solution more basic than Mg(OH)2 solution?

A

Because NaOH dissociates more easily than Mg(OH)2 i.e. Mg(OH)2 is less soluble.

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6
Q

What is the general reaction between a period 3 element and oxygen?

A

Element + Oxygen —-> Oxide

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7
Q

What oxide formation reactions for period 3 elements are described as vigorous?

A

Those forming Na2O and MgO

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8
Q

What period 3 element reacts ‘steadily’ with oxygen?

A

Sulphur.

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9
Q

What period 3 elements react slowly with oxygen?

A

Aluminium and Silicon.

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10
Q

What period 3 element spontaneously combusts in oxygen and what oxide does it form?

A

Phosphorous, P - it forms P4O10

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11
Q

What colour is sodium’s flame?

A

Yellow

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12
Q

What colour are Magnesium and Phosphorous’ flames?

A

Brilliant white.

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13
Q

What colour is sulphur’s flame?

A

Blue

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14
Q

Why is it that Na2O, MgO and Al2O3 all have high melting points?

A

They all have giant ionic lattices in which there are strong electrostatic attractive forces between oppositely charged ions, attractions which require lots of heat energy to break.

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15
Q

In what order are the melting points of Na2O, Al2O3 and MgO?

A

MgO has the highest melting point, then Al2O3, then Na2O.

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16
Q

Why is it that Al2O3’s melting point is lower than MgO’s?

A

Because Al2O3’s ionic bonds have covalent character, whereas MgO’s do not. This is because Al3+ distorts the O2- electron cloud, withdrawing electron density from it.

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17
Q

In what order are the melting points of the period 3 oxides?

A

MgO is highest - ionic lattice

Al2O3 - ionic lattice

SiO2- macromolecular

Na2O - ionic lattice

P4O10- simple molecular

SO2 - simple molecular

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18
Q

Which oxides are acidic and which oxides are basic?

A

Purely ionic oxide solutions are basic - MgO and NaOH (ph 9 and 13 respectively)

Covalent oxides are acidic in solution - H3PO4, H2SO4, H2SO3

Silicon dioxide is insoluble but reacts with bases.

Al2O3 is amphoteric and insoluble.

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19
Q

What is formed when an acid and base react?

A

The salt of the acid and water.

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20
Q

What is the reaction between Al2O3 and NaOH?

A

Al2O3 + 2NaOH —-> 3H2O + 2NaAl(OH)4

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21
Q

What is the reaction between SiO2 and NaOH?

A

SiO2 + 2NaOH —-> Na2SiO3 + H2O

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22
Q

What is the reaction between P4O10 and NaOH?

A

P4O10 + 12NaOH —-> 4Na3PO4 + 6H2O

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23
Q

What is reduction?

A

Electron gain

24
Q

What is oxidation?

A

Electron loss/donation

25
Q

What is a reducing agent?

A

An electron acceptor.

26
Q

What is an oxidizing agent?

A

An electron acceptor.

27
Q

What are half equations allowed to include, besides the substance?

A

e-, H2O and H+

28
Q

How does an electrochemical cell work?

A

Via. two electrodes in solutions of their metals - one electrode is oxidized, releasing electrons into the circuit which flow to the other electrode, causing that electrode’s solution to be reduced, forming its metal.

29
Q

What does a very negative electropotential for a substance suggest about that substance?

A

That it loses electrons easily i.e. it is easily oxidized.

30
Q

What does a highly positive electropotential suggest about a substance?

A

That the substance is difficult to oxidize and is likely to be reduced - gain electrons.

31
Q

What are the drawing conventions for an electrochemical cell?

A

The electrode with the more negative electropotential is on the left and the solutions go in the centre.

¦ means state difference

¦¦ is the salt bridge

no symbol apart from a commar between substances in the same state that aren’t separated by the salt bridge.

32
Q

Which is more reactive, a metal with a low electropotential or a high electropotential?

A

A metal with a low electropotential - one that loses electrons easily.

33
Q

What is the cell potential equation?

A

Ecell = ERHS- ELHS

34
Q

Why is it that conditions affect electrode potential?

A

Because the reactions which occur on the electrode are reversible.

35
Q

Describe and write the cell equation for the hydrogen electrode.

A

Description: A cylinder filled with hydrogen gas and containing a platinum block on the left-hand side, inside a 1M H+ solution, connected to the electrode whose standard potential is being measured.

Pt ¦ H2(g)¦ H+(aq) ¦¦ Zn2+(aq)¦ Zn(s)

36
Q

Define the term ‘standard electrode potential’

A

The standard electrode potential of a half-cell is the voltage measured under standard conditions when the half-cell is connected to a standard hydrogen electrode.

37
Q

What are the conditions for measuring standard electrode potential?

A

100kPa

1M solutions

298K

38
Q

What is the evidence that electrons are transferred in redox reactions?

A

Electrochemical cells - a current flows between two cells, suggesting that electrons are being lost by one substance and gained by the other.

39
Q

Which is more reactive, a non-metal with a very negative electropotential or a non-metal with a very positive electropotential?

A

The non-metal with the more positive electropotential is the most reactive.

40
Q

What type of chemical reactions occur in non-rechargable batteries? What happens when recharging is attempted? Why is this?

A

Irreversible reactions - recharging them may cause them to leak or explode. This is because the anode sometimes forms the casing of the battery and corrodes as the battery is used/ the anode is oxidized.

41
Q

Why is it that zinc-carbon dry cells are non-rechargable?

A

They evolve ammonium ions which react to form hydrogen gas which further escapes from the battery - without this H2, the ammonium ions cannot be reformed.

42
Q

How are rechargable batteries recharged?

A

By supplying a current to them; this forces the electrons to flow in the opposite direction, reversing the chemical reactions.

43
Q

Describe a lead-acid battery. Are they rechargable or non-rechargable?

A

A lead (IV) dioxide anode, a lead cathode, all of which is immerse in a sulphuric acid electrolyte - lead sulphate forms on both electrodes. They are rechargable.

44
Q

Name three type of rechargable battery.

A

Lead-acid, NiCad, Lithium ion..

45
Q

What is a zinc-carbon dry cell?

A

A zinc anode, manganes dioxide and carbon cathode, with ammonium chloride paste for the electrolyte.

46
Q

Define the term ‘anode’

A

The electrode from which positive charge flows (the positive electrode).

47
Q

Define the term ‘cathode’

A

The electrode towards which positive charge flows - the negative electrode.

48
Q

What are the advantages of rechargable batteries over non-rechargbles?

A

Rechargables cost more initially, but can be reused and are therefore cheaper.

Rechargables are less lasting, but can be reused.

Rechargable batteries are able to supply more power than non-rechargables.

Rechargables are less wasteful.

Rechargables contain toxic lead and cadmium and pollute water less.

49
Q

Describe a fuel cell.

A

Hydrogen an oxygen gases are fed into seperate platinum-catalyst-containing electrodes. These electrodes are seperated by an ion exchange membrane, which allows protons to pass through but not electrons. The hydrogen is fed to the negative electrode, where it dissociates to form H+and electrons. The electrons pass throught the circuit towards the positive electrode. Oxygen at the positive electrode reacts with the H+ ions to form water.

50
Q

Why is it that fuel cells cannot be described as carbon-neutral?

A

Because electricity produced through the burning of fossil fuels is used to hydrolyse water to produce hydrogen for the cells.

51
Q

What is a potential issue behind using hydrogen as a fuel?

A

It is highly flammable and could be dangerous.

52
Q

What element features change across the period from left to right?

A

Proton number increases

Shell number/ shielding is constant

Atomic radius decreases

Electronegativity increases

53
Q

Why is it that electronegativity increases across a period, from left to right?

A

From left to right, proton number increases and atomic radius decreases. This means that the ability of the atom to attract the bonding electron pair in a covalent bond increases across the group from left to right because its nucleus is closer and more strongly attracted to it.

54
Q

Why is it that the ability of an element to form a strong covalent bond increases going up a group?

A

Electron shielding and atomic radius decrease up the group, allowing the bonding pair between a given element’s electrons to get closer to the nucleus and be more strongly attracted by it.

55
Q

Why do ionic bonds form?

A

Because of a large difference in electronegativity between the bonding atoms.

56
Q

What is meant by modelling a substance using a perfect ionic model?

A

Regarding ions in the substance as point charges.

57
Q
A

A2 Chemistry (11 decks)

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