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Chemistry additional edexcel > C2.3 Covalent compounds and separation techniques > Flashcards

C2.3 Covalent compounds and separation techniques Flashcards

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1
Q

What are most non-metal compounds held together by?

A

Covalent bonds

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2
Q

What are covalent bonds?

A

A bond formed when a pair of electrons is shared between two atoms

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3
Q

What shell do the electrons making a covalent bond come from?

A

The outermost shell

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4
Q

What is a molecule?

A

Two or more atoms joined together by covalent bonds

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5
Q

What is a dot and cross diagram used for?

A

Showing electronic structures in covalent substances

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6
Q

Why can covalent bonds form between non-metal elements?

A

Non-metal elements all don’t have enough electrons to have a full outermost shell

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7
Q

What is the bond that allows atoms to share two pairs of electrons called?

A

A double bond

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8
Q

What are simple molecular covalent substances?

A

A substance with molecules that are being held together with strong covalent bonds, but that have weak forces between themselves

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9
Q

Why are simple molecular covalent substances poor conductors of electricity?

A

The atoms in simple molecular covalent substances have not lost or gained any electrons and so there aren’t any charged particles that can move around

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10
Q

Why do simple molecular covalent substances have low melting and boiling points?

A

Because there are weak forces between neighbouring molecules, so it doesn’t take a lot of thermal energy to break the bonds

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11
Q

What are giant molecular covalent substances?

A

Billions of atoms all joined together by covalent bonds

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12
Q

What two substances can covalent compounds form?

A
  • simple molecular covalent substances

- giant molecular covalent substances

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13
Q

Why do giant molecular covalent substances have high melting and boiling points?

A

Because all the atoms are joined together by strong covalent bonds, and a lot of thermal energy is needed to break them

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14
Q

What two atoms is sand made out of?

A

Silicon and oxygen

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15
Q

What two different types of giant molecular structure can carbon form?

A

Diamond and graphite

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16
Q

Why do diamond and graphite have very different properties?

A

Because of the way the carbon atoms are arranged

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17
Q

What are two properties of diamond?

A
  • it’s very hard

- it doesn’t conduct electricity

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18
Q

What are the properties of graphite?

A
  • easily rubs away in layers
  • soft enough to be used as a lubricant
  • conducts electricity
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19
Q

Why does graphite easily rub away in layers?

A

Because there are strong covalent bonds within layers but weak forces between the layers

20
Q

What do immiscible liquids do?

A

Not mix completely with each other

21
Q

What happens when you shake immiscible liquids?

A

They seem to mix but soon separate out again

22
Q

How can you separate immiscible liquids?

A

Using a separating funnel

23
Q

What happens when two liquids dissolve in each other?

A

Their particles mix completely to form a solution

24
Q

What is a miscible solution?

A

A solution where two mixed liquids do not separate out once mixed

25
Q

How can you separate out a miscible solution?

A

Through fractional distillation

26
Q

Why does fractional distillation work on separating miscible liquids?

A

Because they have different boiling points

27
Q

What happens during fractional distillation?

A
  • the mixture of liquids is heated and the liquids evaporate
  • the vapours condense in a fractionating column
  • the fraction with the highest boiling point condenses near the bottom of the column, and the fraction with the lowest boiling point condenses near the top
28
Q

What must be done before the mixture of liquids is heated for fractional distillation?

A

Nitrogen and water must be taken out of the air

29
Q

How is water taken out of air in preparation for fractional distillation?

A

The air is cooled so that the water can freeze and be removed

30
Q

What happens to the remaining air once the water has been removed in preparation for fractional distillation?

A

It is cooled to -200*C to be liquefied

31
Q

How is nitrogen taken out of the air when preparing for fractional distillation?

A

The liquefied air is warmed up to -185*C to cause the nitrogen to evaporate and go to the top of the column

32
Q

What happens to oxygen once nitrogen and water have been taken out in preparation for fractional distillation?

A

It stays as a liquid and is piped out the bottom of the column

33
Q

What part of the fractional distillation column is the coldest?

A

The top

34
Q

Why is the column warmed up to -185*C ?

A
  • 185*C is above the boiling point of nitrogen so the nitrogen boils and evaporates
  • 185*C is below the boiling point of oxygen so the oxygen stays a liquid
35
Q

What difference between compounds does chromatography use to separate different components of a mixture?

A

Their solubilities

36
Q

How does paper chromatography work?

A
  • samples at are placed near the bottom of a special sheet of paper
  • the bottom of the paper is placed touching the solvent but not the samples
  • as the solvent travels up the paper it carries the different samples at different speeds so they are separated
37
Q

What is the sheet of paper produced as a result of paper chromatography called?

A

A chromatogram

38
Q

Why is a lid used during paper chromatography?

A

To stop the solvent evaporating

39
Q

What is the R_f value?

A

The distance the compound has risen divided by the distance the solvent has risen

40
Q

What are R_f values used for?

A

Identifying different compounds

41
Q

What are three uses of chromatography?

A
  • to identify food colourings and to check the safety of food
  • to identify DNA samples to work out if suspects have been at a crime scene
  • to analyse paints and dyes to restore paintings
42
Q

What structure is sand made out of?

A

Giant covalent

42
Q

Why is diamond very hard?

A

All the atoms are joined together with strong covalent bonds

42
Q

Why doesn’t diamond conduct electricity?

A

There are no free electrons to move around

43
Q

Why does graphite conduct electricity?

A

There is one electron from each carbon atom that can move along the layers

44
Q

How cold is the top of a fractional distillation column?

A

-190*C

Chemistry additional edexcel (6 decks)

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