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Chemistry > CC2 > Flashcards

CC2 Flashcards

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1
Q

What are some features of the composition of a pure substance?

A
  1. The composition cannot be changed.
  2. The composition is the same in all parts of a piece of the substance (e.g. pure gold contains only gold atoms).
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2
Q

What is a compound?

A

A substance that can be split into simpler substances because it contains the atoms of two or more elements joined together.

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3
Q

What is a mixture?

A

A substance containing two or more different substances that are not chemically joined together. You can use physical processes to separate mixtures into different substances.

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4
Q

What is an example of a compound?

A

Sugar used at home os a compound called Sucrose. It contains carbon, hydrogen, and oxygen atoms chemically bonded together to form sucrose molecules.

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5
Q

What is an example of a mixture?

A

Air is a mixture of gases. It is a mixture as its composition changes (from oxygen to carbon dioxide).

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6
Q

What is a pure substance?

A

A substance that has the same fixed composition in all its parts (so it cant be separated into other substances using physical methods).

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7
Q

What happens to the weak forces of attractions when a solid melts?

A

When a solid melts, its particles gain enough energy to overcome the weak forces of attraction between them. They move further away from one another and the solid becomes a liquid. The temperature at which this happens is the melting point.

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8
Q

What is a physical property?

A

A description of how a material behaves and responds to forces and energy. For example, hardness is a physical property.

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9
Q

What is a chemical property?

A

How a substance reacts with other substances.

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10
Q

What are the physical properties of a pure substance?

A

All of the pure substance will melt at the same temperature until all of the substance has changed state.

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11
Q

Do mixtures have a sharp melting points?

A

No, a mixture doesn’t have a sharp melting point.

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12
Q

How can you tell the difference between a pure and impure substance in a heating curve?

A

A pure substance has a sharp melting point (flat curve on melting point) and curved gradual lines whereas an impure substance has straight lines and doesn’t have a sharp melting point (line is not flat on melting point).

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13
Q

How can filters be used and how do they work?

A

To separate some mixtures. They let smaller pieces or liquids through but trap bigger pieces or insoluble substances.

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14
Q

What is a solvent?

A

Describes the liquid in which a substances dissolves to make a solution.

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15
Q

What is a solute?

A

Describes a substance that dissolves in a liquid to make a solution.

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16
Q

What is the difference between a solute and a solvent?

A

Solute: The substance that dissolves in a liquid (e.g. Salt in Sea Water).
Solvent: The liquid in which a substance dissolves in (e.g. Pure water in Sea Water).

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17
Q

How can solutes be separated from a solution?

A

By evaporating the solvent to leave the solutes behind. This process is called crystallisation.

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18
Q

What is formed during crystallisation?

A

The process forms solid crystals of various sizes. If the crystals form slowly, the particles have longer to form an ordered pattern and will make larger crystals.

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19
Q

What is a saturated solution?

A

A solution that contains the maximum amount of solute that can dissolve in that amount of solvent at that temperature.

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20
Q

How do you filter and crystalize a solution in a laboratory?

A

To filter a solution in the lab, a filter tunnel is lined with filter paper that has fine holes in it. The solvent and solute(s) pass through the fine holes to form the filtrate. Bits of insoluble substances cannot fit through the holes and so leave a residue in the filter paper. A bunsen burner is then used to evaporate the filtrate carefully. Care must be taken not to overheat the solution once it is saturated, because hot crystals may spit out. Further heating may also cause crystals to change chemically.

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21
Q

What is the filtrate?

A

A solution that has passed through a filter.

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22
Q

What is the residue?

A

Material remaining in the filter after a mixture has passed through it.

23
Q

What laboratory apparatus is needed for filtration?

A

Filter paper, Suspension, Beaker, Filter funnel.

24
Q

What laboratory apparatus is needed for crystallisation?

A

Evaporating basin, Filtrate, Boiling water, Gause, Bunsen burner.

25
Q

What is a risk assessment?

A

Identification of the hazards of doing an experiment and ways of reducing the risk of harm from those hazards.

26
Q

What is a hazard?

A

Something that could cause harm.

27
Q

What is a risk?

A

The chances of something that could cause harm happening.

28
Q

What is a risk assessment for crystallisation?

A

The risks from spitting can be reduced by wearing eye protection, Removing the bunsen burner before the solution is completely dry and Using steam to heat the evaporating basin gently.

29
Q

What is Chromatography?

A

A technique for separating the components of a mixture (e.g. different food colouring agents)

30
Q

How does paper chromatography work?

A

It is a simpler technique that works because some compounds dissolve better in a solvent than others. This means we can easily distinguish the compounds from each other.

31
Q

What is the mobile phase?

A

In paper chromatography, this is when the solvent moves along the paper carrying dissolved samples with it (e.g. water).

32
Q

What is the stationary phase?

A

The surface through which the solvent and dissolved substances move in chromatography (e.g. paper).

32
Q

What is a chromatogram?

A

The piece of paper showing the results of chromatography.

33
Q

What is the formula for the Rf value?

A

Rf value= distance moved by the spot/distance moved by the solvent

34
Q

What can paper chromatography be used for?

A
  1. To distinguish between pure and impure substances.
  2. To identify substances by comparing the pattern on the chromatogram with the patterns formed by known substances.
  3. To identify substances by calculating their Rf values.
35
Q

How can you make water pure?

A

To make water pure, you need to separate it from the dissolved solids. This is done by distillation.

36
Q

What is distillation?

A

The process of separating a liquid from a mixture by evaporating the liquid and then condensing it (so it can be collected).

37
Q

What is the process of distillation?

A
  1. The solution (e.g. mineral water) is evaporated and so only the liquid (e.g. water) is turned to a gas (vapour). The solids (e.g. Solid minerals) which have a much higher boiling point are left behind.
  2. The water vapour (steam) is pure. If the vapour is then condensed, it turns back into liquid water again, only this liquid water will now be pure.
38
Q

What apparatus is needed for a simple still?

A

Bunsen burner, Conical flask, Delivery tube, Test tube, Tripod.

39
Q

What apparatus is needed for distillation?

A

Distillation flask, Thermometer, Condenser, Cooled water, Delivery tube, Beaker.

40
Q

Why is the simple still method not that effective?

A

It isn’t very efficient because much of the water vapour is lost in the delivery tube.

41
Q

Why is the distillation method quite effective?

A

It is quite efficient as the condenser keeps the tube cool, so that almost all of the vapour condenses and turns into a liquid.

42
Q

What apparatus is needed for fractional distillation?

A

Round bottom flask, Fractional column, Thermometer, Condenser, Cooled water, Delivery tube, Beaker.

43
Q

What is fractional distillation?

A

A method of separating a mixture into two or more liquids.

44
Q

What can fractional distillation be used for?

A
  1. To separate the different products in crude oil.
  2. To make alcoholic drinks such as whiskey and vodka.
  3. To separate out the gases in the air, after the air has been cooled and turned into a liquid at -200°c.
45
Q

What is desalination?

A

A process that produces fresh drinking water by separating the water from the salts in salty water.

46
Q

How can desalination simply be achieved?

A

Desalination can simply be achieved by using the process of simple distillation.

47
Q

How does simple distillation for desalination work?

A

Water is separated from dissolved salts using simple distillation. Sea water is heated so that water vapour leaves it quickly. This vapour is then cooled and condensed, forming water without the dissolved salts.

48
Q

Is simple distillation a suitable method for producing large volumes of drinking water?

A

No, as a lot of energy must be transferred to sea water during simple distillation which will be a challenge for larger amount.

49
Q

What is chemical analysis?

A

Using chemical reactions or sensitive machines to identify and measure the substances in a sample.Chemical analysis requires the water in it to have no dissolved salts.

50
Q

What steps are used to deal with objects that are in drinking water that comes from rivers or lakes?

A
  1. Using a sieve.
  2. Sedimentation.
  3. Filtration using tanks containing beds of sand and gravel.
  4. Chlorination.
51
Q

What is sedimentation?

A

The process in which rock grains and insoluble substances sink to the bottom of a liquid.

52
Q

What is chlorination?

A

The process of adding chlorine to a substance, often to water, in order to kill bacteria.

Chemistry (17 decks)

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