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Chemistry A > 1) Relating properties to uses and production of substances > Flashcards

1) Relating properties to uses and production of substances Flashcards

1
Q

What are bases and give examples

A

Bases that are substances that accept hydrogen ions H+, also known as proton acceptors.

Examples: Metal oxides, metal hydroxides

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2
Q

What does the oxide ion do in metal oxides? Give an example

A

Accept protons and neutralise acids.

Calcium oxide will neutralise sulfuric acid to form calcium sulphate

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3
Q

What is the alternative name for calcium oxide?

A

Lime

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4
Q

What is the use of calcium oxide?

A

It is used in agriculture to neutralise acidic oil

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5
Q

Why is the use of calcium oxide important?

A

Because if the pH of soil is too low, the plant will absorb toxic ions that will affect root growth

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6
Q

How are metal hydroxides formed?

A

Metal hydroxides are formed when metal oxides react with water

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7
Q

What do hydroxide ions in metal hydroxides do?

A

Accept protons and neutralise acids

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8
Q

What is amphoteric oxide?

A

Amphoteric oxides can behave as either acids or bases

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9
Q

Where are the elements located on the periodic table that form amphoteric oxides give an example.

A

They tend to be in the middle of a period, e.g. aluminium

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10
Q

Is aluminium oxide dissolvable?

A

No

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11
Q

How does aluminium oxide react as a base?

A

It would react with acids to form a salt and water. E.g.

Al2O3 (s) + 6HCl (aq) –> 2AlCl3 (aq) + 3H20 (l)

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12
Q

How does aluminium oxide react as an acid?

A

It would react with bases to form aluminates. E.g. it would react with NaOH to form sodium tetrahydroxoaluminate, which is used in the Bayer process to convert bauxite to aluminium oxide.

Al2O3 _2NaOH + 3H2O –> 2NaAl(OH)4

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13
Q

What is alumina?

A

A form of aluminium oxide

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14
Q

Where is alumina found?

A

It is found in the mineral bauxite, and its extracted and purified using the Bayer process.

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15
Q

What is the Bayer process?

A

1) Crush the bauxite
2) React with NaOH (aq) at 170C to form NaAl(OH)4 (aq)
3) Filter out the solid impurities
4) Allow to crystalise to form Al(OH)3
5) Heat in rotary kiln to form Al2O3

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16
Q

How is the alumina produced by the Bayer process used?

A

In the Hall-Heroult process to form aluminium by electrolysis

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17
Q

What is another use of alumina?

A

Used as a refractory material in kilns

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18
Q

What is a refractory material?

A

Materials that retain their strength and are chemically stable at high temperatures.

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19
Q

What is another term for bauxite?

A

Aluminium ore

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20
Q

How does bauxite turn into aluminium?

A

Bauxite is mined and then processed through the Bayer process to form alumina, also known as aluminium oxide. Molten alumina is then electrolysed using the Hall-Heroult process

21
Q

Why is cryolite added to alumina?

A

To lower the melting point and to save energy.

22
Q

What acts as the negative electrode (cathode) in the extraction of aluminium?

A

The carbon lining of the steel tank

23
Q

What are the steps of extraction of aluminium (Hall-Heroult process)

A

1) Aluminium ions are reduced to form molten aluminium

Reaction at cathode=Al3+ + 3 e− → Al

2) The molten aluminium can then be drained off and cast into ingots

3) The anodes are made from carbon, where oxide ions are oxidised to form oxygen gas
2O2- —> O2 + 4e-

24
Q

Why do carbon electrodes have to be replaced regularly after Hall-Heroult process?

A

They react with oxygen as it forms during the process

25
Q

What is the main titanium ore and what does it contain?

A

Rutile, which contains titanium (IV) dioxide, TiO2

26
Q

Why is titanium not extracted by electrolysis like aluminium, even though they have a similar reactivity?

A

It is not generally extracted by electrolysis as titanium forms tree-like crystals which can affect the electrodes.

And side reactions with titanium ions at both electrodes can form impurities.

27
Q

What is the name of the process called to extract titanium?

A

Kroll process

28
Q

What are the steps in the Kroll process?

A

1) Titanium (IV) dioxide, coke, and chlorine are heated together at 900C to form titanium (IV) chloride

2)Magnesium is used as a reducing agent to form titanium

29
Q

Why is the Kroll process expensive?

A

It is expensive due to the large amounts of energy needed to create the very high temperatures involved.

30
Q

What are the further disadvantages of the Kroll process?

A

The magnesium used in the process is produced by an energy intensive electrolysis process.

It is time consuming as it is a batch process , which means the reactor has to be shut down and cooled before the titanium can be removed for purification, which is when impurities is removed by further heating.

31
Q

What is more stiff, aluminium or titanium?

A

Titanium

32
Q

What is more strong, aluminium or titanium?

A

Titanium

33
Q

What is more dense, aluminium or titanium?

A

Titanium

34
Q

How much cheaper is aluminium compared to titanium?

A

Titanium is 46x more expensive than aluminium.

35
Q

Do aluminium and titanium corrode?

A

No, they both have a high resistance to corrosion

36
Q

What is the electrolysis of brine?

A

A solution of NaCl (aq) produces chlorine, hydrogen, and sodium hydroxide when electrolysed.

37
Q

What is the reaction at the anode for the electrolysis of brine?

A

Chloride ions react at the anode to form chlorine gas. 2CL- (aq) —> Cl2 (g) + 2e-

Each chloride ion has lost an electron so the reaction is OXIDATION

38
Q

What is the reaction of the cathode for the electrolysis of brine?

A

Hydrogen ions from the water react at the cathode to produce hydrogen gas. 2H+(aq) + 2e- –> H2 (g)

Each hydrogen ion has gained an electron so the reaction is REDUCTION.

39
Q

What happens to the remaining ions in the electrolysis of brine?

A

The remaining sodium +hydroxide ions stay in solution, forming sodium hydroxide solution, often known as caustic soda

40
Q

What is the structure of a diaphragm cell?

A

It has a diaphragm dividing the cell, and this is porous so it allows brine to pass from one side to the other.

41
Q

What does the asbestos diaphragm prevent?

A

It prevents chlorine and hydrogen gas from passing though, so gases are kept separate.

42
Q

What happens to the sodium hydroxide in the diaphragm cell?

A

The sodium hydroxide formed is still mixed with brine, it is more soluble than sodium chloride, so sodium chloride can be recrystallised to be remove most of it

43
Q

What type of divide does a membrane cell have?

A

An ion- exchange membrane.

44
Q

What does the ion-exchange membrane do?

A

Allows positive sodium ions to pass through, but will not allow negative chloride ions from the anode to the cathode.

45
Q

How does the brine (sodium chloride) enter the membrane cell?

A

Through the anode side, so the sodium hydroxide left over at the cathode side is not contaminated by the sodium chloride

46
Q

What is a pro of the diaphragm cell?

A

Cheaper to construct

47
Q

What are the cons of the diaphragm cell?

A

Needs replacing regularly
Purity of sodium hydroxide produced is low
Cell uses slightly more energy per tonne of chlorine produced

48
Q

What are the pros of the membrane cell?

A

Needs little maintenance
Purity of sodium hydroxide produced is high
Cell uses slightly less energy per tonne of chlorine produced

49
Q

What are the cons of the membrane cell?

A

More expensive to construct

Chemistry A (3 decks)

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