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Chemsitry > Chemical Changes & Separating & Purifying Substances > Flashcards

Chemical Changes & Separating & Purifying Substances Flashcards

1
Q

What is “Soluble”?

A

A substance which can be dissolved

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2
Q

What is “Insoluble”?

A

A substance which cannot be dissolved

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3
Q

What is a “Precipitate”?

A

+An insoluble solid +You have 2 solutions, - You mix them and make a precipitate {depends]

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4
Q

What is the Rf formula

A

Rf = distance travelled by sample

distance travelled by solvent

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5
Q

What are Common salts of sodium,
potassium and ammonium?

A

Soluble

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6
Q

What are Nitrates?

A

Soluble

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7
Q

What are Common chlorides?

A

Soluble [except silver chloride
and lead chloride]

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8
Q

What are Common sulfates?

A

Soluble [except lead, barium and
calcium sulfate]

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9
Q

What are Common carbonates and
hydroxides?

A

Insoluble [except for sodium,
potassium and ammonium ones]

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10
Q

How can you predict precipitates?

A

They swap partners

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11
Q

+How do you find an insoluble salt? [Lead chromate]

+What is the process of filtration/purification?

A
  1. Measure 20 cm3 of sodium chloride into a 100 cm3 beaker.
  2. Add 10 cm3 of lead nitrate.
  3. Gently shake the mixture and then filter through folded filter paper. Wash it through with distilled water.
  4. Allow the solid to dry. This is now the pure, dry insoluble salt.
  5. Dispose of the solid and solutions as directed by your teacher.
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12
Q

What do chemists mean by pure?

A

+In chemistry, pure means containing only one kind of element or compound

+a pure substance consists only of one element or one compound

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13
Q

What do impure compounds [mixtures] have?

A

+Impure compounds have a range of melting points and boiling points,

+the different substances they contain melt or boil at different temperatures.

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14
Q

What do pure compounds have?

A

pure compounds have definite melting points and boiling points.

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15
Q

What is th process for crystalisation?

A
  1. Measure out 30cm3 of copper sulphate solution in a measuring cylinder
  2. Place in an evaporating basin on a gauze over a Bunsen burner
  3. Warm gently to evaporate water. Attempt to evaporate one third to one half of the liquid. If you see crystals forming then turn off the Bunsen

DO NOT HEAT TO DRYNESS!!!

  1. Allow to cool
  2. Collect crystals by filtration
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16
Q

What is crystalisation?

A

+Separates a soluble solid from a solution

+is good if you want to purify a soluble compound

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17
Q

How do you do crystalisation?

A
  • •Dissolve the solid in a small amount of hot solvent
  • •Gently heat to evaporate some of the solvent. Then cool.
  • •Slowly crystals will appear.
  • •These should be pure
  • •You could check by seeing if the melting point is sharp
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18
Q

What is chromatography?

A

Technique to separate mixtures of soluble compounds and identify them

19
Q

Where is chromatography used?

A

Identification of drugs (eg athletes; identification of E numbers in food

20
Q

What is the process for chromatography?

A
  1. Draw a pencil line 1.5 cm from the bottom of the paper
  2. Place a spot of the mixture on the line
  3. Place the paper in a beaker with solvent (eg water or ethanol) at the bottom
  4. The solvent MUST be lower than the pencil line
  5. Allow the solvent to run up the paper. As the solvent moves up the paper the solvent separates the compounds
  6. The properties of the compound (eg solubility) determine how far up the compounds move
21
Q

M LG

What is the moblile phase?

A

+Where the molecules can move. This is always a liquid or gas

22
Q

What is the stationary phase?

A

Where the molecules can’t move. This can be a solid or a really thick liquid

23
Q

In paper chromatography, what is the stationary phase?

A

A piece of filter paper

24
Q

What is the mobile phase in paper chromatography?

A

A solvent [water or ethanol]

25
Q

Solubility table

A
26
Q

What two things does the amount of time the molecules spend in each phase depend on?

A
  • How soluble they are in the solvent
  • How attracted they are to the stationary phase
27
Q

MS CFP

What happens to molecules with a higher solubility in the solvent?

A

They will spend more time in the mobile phase than the stationary phase

+So they’ll be carried further up the paper

28
Q

S LfromS

What is simple distilation?

A

A process that separates out a liquid from a solution

29
Q

What is fractional distilation?

A

A process to separate a mixture of liquids

30
Q

What is the process of simplle distillation?

A
31
Q

What is a mixture?

A

a mixture consists of two or more different substances, not chemically joined together

32
Q

What is the process of fractional distilation?

A
33
Q

What are some water resources in the UK?

A
  • Lakes
  • Rivers
  • Reservoirs
  • Aquifers
  • Grey water [recycled domestic waste water]
34
Q

What are the stages of purification?

A
  1. Filtration
  2. Sedimentation
  3. Chlorination
35
Q

What is filtration [water]?

A

+A mesh wire screen out large sediment particles

+Gravel and sand beds filter out any other solid bits

36
Q

What is sedimentation? [w]

A

+Iron/aluminium sulfate is added to water

+ - makes fine particles clump together and settle at the bottom

37
Q

What is chlorination [w]?

A

+Chlorine gas is bubbled through water to kill harmful bacteria and other microbes.

38
Q

What is one unique way of getting potable water?

A

+In some dry countries [Kuwait] - sea water is distilled to produce drinking water

39
Q

Why isn’t distilation used in the UK?

A

+Distilation needs lots of energy

+ So its really expensive - especially when producing large quanttities of fresh water

40
Q

What must water in chemical analysis be?

A

Pure

+Deionised water should be used

41
Q

What is deionised water?

A

+Water that has had the ions [calcium, iron] that are in normal tap water removed

42
Q

Why should deionised water be used in chemical analysis?

A

+Ions in normal water [although present in small amounts] can interfere with reactions

+Using normal water could give an experiment a false result

43
Q

What is the solvent front?

A

The highest point the solvent should move

Chemsitry (5 decks)

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