C2 Flashcards

1
Q

What are the two phases in chromatography?

A

`A stationary phase that does not move. A mobile phase that does move

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2
Q

What is the stationary phase in paper chromatography?

A

The absorbent paper

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3
Q

What is the stationary phase of gas chromatography?

A

Silica or alumina powder packed into a metal column

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4
Q

Why can carbon form many different compounds?

A

It has 4 valence electrons and can form 4 covalent bonds. It can join with other carbon atoms to form chains and rings or form covalent bonds with other elements

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5
Q

Why are diamond and graphite different?

A

Because they have different structure and bonding

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6
Q

What is a nanotube?

A

A sheet of graphene rolled into a tube. Strong. Used to reinforce some sports equipment.

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7
Q

Why are metals malleable?

A

Metal ions are held in a lattice by forces that attract them to a sea of delocalised electrons. When a large enough force is applied layers of metal ions slide over one another but delocalised electrons are free to move so overall no bonds are broken.

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8
Q

What is a material made from nanoparticles called?

A

Nanoparticulate

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9
Q

Risks of nanoparticles

A
  • May be breathed in, absorbed by skin or pass into cells
  • May take a long time to break down once released into environment and toxic substances may stick to their surfaces
  • Harmful to health and environment in ways difficult to predict, with risks difficult to determine
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10
Q

What is bonding in a simple molecule like?

A
  • Covalent bonds involve electrostatic forces of attraction but the forces are between the nucleus of each bonded atom and the shared electrons
  • Covalent bonds are strong. Intermolecular forces are weak.
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11
Q

What is a phase?

A

A substance in the solid, liquid or gas state.

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12
Q

What is the mobile phase in paper chromatography?

A

A solvent in the liquid state

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13
Q

What is thin layer chromatography?

A

Same way as paper chromatography, but stationary phase is a thin layer of silica or alumina powder spread over a plate of glass or plastic

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14
Q

What are Rf values?

A

Compare the different spots on a chromatogram

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15
Q

What is the mobile phase in gas chromatography?

A

Inert carrier gas such as nitrogen

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16
Q

What does gas chromatography do?

A

Separates components and measures their amounts

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17
Q

What happens in gas chromatography?

A
  • Sample is turned into gas state and injected into column
  • Different components take different times to travel through the column, depending on how strongly they bind to the stationary phase
  • A detector sends a signal to a computer as each component leaves the column
  • The computer produces a chromatogram in which each component is a peak plotted against the travel time
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18
Q

How to calculate Rf values?

A

Distance travelled by substance/distance travelled by solvent

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19
Q

What are the advantages of thin-layer chromatography?

A

Quicker, more sensitive, there are more choices of stationary phases and solvents to use

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20
Q

How to choose separation method?

A
  • Insoluble and soluble substance -filtration
  • A solute dissolves in solvent - crystallisation or simple distillation
  • Two or more liquids-fractional distillation
  • Coloured soluble substances- paper or thin-layer chromatography
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21
Q

What is a diamond like?

A
  • Transparent and very hard
  • Exists as a giant covalent structure where each carbon atom is covalently bonded to 4 other carbon atoms
  • Has very high melting point
  • No delocalised electrons as all valence electrons are shared so it doesn’t conduct electricity.
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22
Q

What is an allotrope?

A

Different forms of an element in the same state but with different atomic arrangements

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23
Q

What is graphite like?

A
  • Grey-black and soft
  • Giant covalent structure where each carbon atom is covalently bonded to three other, so one electron is not shared so it becomes delocalised and is free to move through the structure.
  • It conducts electricity even though it is a non-metal. Has a layered structure
  • Atoms in each layer form interlocking hexagons
  • Very high melting point
  • Forces between layers are weak so layers can slide over easily
  • Graphite is hence slippery, used in pencil.
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24
Q

Difference between diamond and graphite

A

Diamond bonded to 4 graphite 3. Diamond is transparent and very hard , graphite is very-black and soft

25
Q

Examples of allotropes of carbon

A

Diamond, graphite, graphene, fullerenes

26
Q

What is graphene like?

A

A single layer of graphite. Almost transparent. Extremely strong and conducts electricity.

27
Q

What is a fullerene like?

A

Comes from large family of carbon allotropes and the molecules are shaped like tubes or balls.

28
Q

What is a buckyball?

A
  • Resembles sheet of graphene closed to make a hollow ball
  • But carbon atoms may be in pentagons as well as hexagons.
  • Have potential uses as lubricants with molecules acting like tiny ball bearings
  • Small size allows buckyballs to pass through cell membranes and might deliver medical drugs directly to cells one day.
29
Q

What happens when a substance melts?

A

Some bonds break going from the solid to the liquid state

30
Q

What happens when a substance boils?

A

All remaining bonds bream going from the liquid to the gas state

31
Q

When do substances have high melting points?

A

If they have many strong bonds in the solid state

32
Q

When do substances have high melting points?

A

If they have many strong bonds in the liquid state

33
Q

What happens when a substance condenses?

A

Some bonds form going from the gas to the liquid state

34
Q

What happens when a substance freezes?

A

Many bonds form going from the liquid to the solid state

35
Q

How is stored chemical energy transferred to the surroundings?

A

Usually by heating , when chemical bonds form

36
Q

Relative strength of a metallic bond

A

Strong

37
Q

Relative strength of an ionic bond

A

Strong

38
Q

Relative strength of a covalent bond

A

Strong

39
Q

Relative strength of intermolecular forces

A

Weak

40
Q

Which substance are usually in the solid state at room temp?

A

Metals, ionic compounds, giant covalent substances

41
Q

What state are simple molecular substances in at room temp?

A

Liquid or gas or solid that is easily melted

42
Q

What does the difference between malleable and brittle depend on?

A

How easily particles in the substance can change their positions in the lattice structure.

43
Q

Why are other substances brittle?

A
  • Giant covalent structures contain very many atoms held together by strong covalent bonds
  • If large enough force applied many covalent bonds break at once so the substance breaks
  • Similar situation for ionic compounds.
44
Q

Simple molecules and polymer molecules are attracted to each other by what? Are they brittle or malleable?

A
  • Weak intermolecular forces which are easily broken

- In solid state and arranged in lattice they may be brittle. If molecules

45
Q

Why do some substances conduct electricity?

A

If it has charged particles that can move. Metals conduct in liquid and solid state. Simple molecules, most polymers and most substances with a giant covalent structure do not conduct electricity as no delocalised electrons.

46
Q

Do ionic compounds conduct electricity?

A

Contain oppositely charged ions. Free to move in liquid state (molten) or when dissolved in solution but not in solid state. So conducts when molten or in solutions but not when solid

47
Q

How big are nanoparticles?

A

1nm-100nm consists of just a few hundred atoms

48
Q

What do nanoparticulate materials have?

A

Different properties to the same substance in bulk

49
Q

What is the small size of nanoparticles useful for?

A

New paints, cosmetics, medicine

50
Q

What are many nanoparticle properties due to?

A

Their very large surface area compared to with the same substance in bulk

51
Q

What developments can nanoparticularw properties lead to?

A

New catalysts to speed up industrial chemical reactions. Self-cleaning windows, oven and clothes

52
Q

What are ionic bonds?

A

Strong electrostatic forces of attraction between oppositely charged ions

53
Q

What is a molecule?

A

Particle in which non metal atoms are joined together by covalent bonds

54
Q

What is a simple molecule?

A

Contains few atoms that are covalently bonded but has weak intermolecular forces that are easily overcome

55
Q

What do giant covalent structures consist of?

A

Many non-metal atoms joined by covalent bonds and arranged in a repeating regular pattern called a giant lattice.

56
Q

Structure of metals

A

Giant metallic lattice

57
Q

How are metallic bonds formed?

A

vElectrons leave outer shells forming a sea of electrons around positively charged metal ions. They are delocalised electrons.

58
Q

What are metallic bonds?

A

The strong electrostatic forces of attraction between the delocalised electrons and the closely packed, positively charged metal ions.