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Y12 Chem > Chemical Analysis > Flashcards

Chemical Analysis Flashcards

1
Q

Element

A

An element is a substance that consists of only one type of atom. They cannot be broken down into simpler substances by chemical means

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2
Q

What is filtration used to separate?

A

Solids from liquids

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3
Q

What is the substance left on the filter paper after filtration?

A

Residue

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4
Q

The liquid that filters through filtration is

A

Filtrate

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5
Q

What is evaporation used to separate

A

Evaporation is used to separate a soluble solid from a liquid.

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6
Q

What is simple crystallisation used to separate?

A

To separate a solution from the solvent and make crystals.

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7
Q

What is fractional distillation used to separate?

A

Separating miscible liquids with different boiling points

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8
Q

Potable water is

A

Water that is safe to drink

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9
Q

Desalination is

A

The process of removing dissolved substances from sea water

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10
Q

Sea water can be made potable by distillation where the sea water is boiled and water is condensed. What are the disadvantages of producing drinking water this way? (3)

A
  • it is expensive because large amounts of energy are needed to heat the sea water
  • it increases the use of fossil fuels which are non-renewable resources
  • carbon dioxide emissions from burning fossil fuels contribute to global warming
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11
Q

What must be treated to kill microorganisms which may cause disease. How is this done?

A

Chlorination

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12
Q

Test for water: add water to anhydrous copper(ii) Sulfate crystals and these will change from…

A

White to blue

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13
Q

Flame test colours:

A

Cation Flame colour

Lithium.            Crimson
Sodium.           Yellow/orange 
Potassium.       Lilac
Calcium.           Brick red
Copper.             Blue/green
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14
Q

Precipitate definition

A

A solid which may be formed on mixing two solutions

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15
Q

Sodium hydroxide solution will form ….. coloured metal hydroxide …… when added to different salt solutions

A

Gelatinous

Precipitates

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16
Q 
Give the colour of solution, colour of precipitate and colour in excess NaOH when cations are present
Cu2+
Fe2+
Fe3+
Mg2+
Al3+
Zn2+
A

Cation. Solution. Precipitate. In excess
Cu2+. Blue. Blue. Nochange
Fe2+. Green. Green. No change
Fe3+. Orange. Red/brown. No change
Mg2+ colourless White. No change
Al3+. Colourless. White. White ppt dissolves to form colourless solution
Zn2+. Colourless. White. White ppt dissolves to form colourless solution

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17
Q

Silver Sulfate

A

2Ag+ (aq) + SO4 2- (aq) -> Ag2SO4 (s)

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18
Q

Silver chloride precipitate colour

A

White

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19
Q

Silver bromide precipitate colour

A

Cream

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20
Q

Silver iodide precipitate colour

A

Yellow

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21
Q

Barium Sulfate precipitate colour

A

White

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22
Q

Iron hydroxide precipitate colour

A

Green

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23
Q

Colour of halide precipitate in silver nitrate
Cl-
Br-
I-

A

Cl- White
Br- cream
I- yellow

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24
Q

Test for Sulfate ions will give a

A

White precipitate

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25
Q

Test for copper ions

A
  • Take a nichrome wire with a loop on the end and clean in concentrated HCl and place in a hot blue Bunsen flame.
  • Dip the clean wire into concentrated acid and then solid metal salt and place in the hottest part of the hot Bunsen flame.
  • If copper is present it will burn with a blue-green colour
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26
Q

Test for Sulfate ions (3)

A
  • Form a solution of salt and water
  • Pour a few cm3 of the solution into a test tube and add barium chloride solution drop wise
  • Observe a white ppt forming if sulfate ions are present in the sample
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27
Q

How would you carry out a flame test (4)

A
  • Light a hot Bunsen flame.
  • Dip the nichrome wire with a loop into the conc HCl and clean in the blue hot Bunsen flame.
  • Dip in the HCl again and then in the metal solid.
  • Hold under the blue flame and observe the colour of the flame
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28
Q

Why does an impure substance have a lower melting point ?

A

The melting point is lower because impurities will disrupt the regular lattice arrangement that is present in most solids and so the bonds between the particles will be weaker

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29
Q

The …. amount of impurity the … the melting point

A

Greater, lower

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30
Q

Why is salt (with grit for grip) added to roads in winter ?

A

To lower the melting point of water so that ice cannot form at 0 degrees

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31
Q

The … the amount of impurity the .. the boiling point

A

Greater, higher

32
Q

How come the boiling point is higher if substances such as ionic compounds dissolve in water ?

A

The boiling point is higher because the water molecules are attracted to the ions and so more energy is required to make the water molecules escape from the water

33
Q

Boiling point definition

A

The temperature at which a liquid changes into a gas

34
Q

Melting point definition

A

The temperature at which a solid changes into a liquid

35
Q

Pure substance definition

A

A single element or compound that is not mixed with any other substance

36
Q

Mixture

A

Defined as two or more substances mixed together, which are usually easy to separate

37
Q

Formulation definition

A

A mixture that has been designed as a useful product and is formed by mixing together several different substances in carefully measured quantities to ensure the product had the required properties

38
Q

Give three examples of formulations

A
  • Alloys
  • Medicines
  • Fertilisers
39
Q

Describe chromatography

A

The separation of mixtures of soluble substances by running a solvent (mobile phase) through the mixture on the paper (stationary phase), which causes the substances to move at different rates over the paper;

40
Q

What substance is added to the contents of the flask during simple distillation to promote smooth boiling ?

A

Anti-bumping granules

41
Q

Why is pencil used in chromatography ?

A

It will not dissolve in the solvent

42
Q

The result of a chromatography experiment is called a ..

A

Chromatogram

43
Q

How to determine the most soluble sample in the solvent on the chromatography paper ?

A

It moves furthest up the chromatography paper

44
Q

How is an Rf value calculated for chromatography

A

Distance moved by spot
——————————-
Distance moved by solvent

45
Q

What is the solvent front ?

A

How far the solvent has travelled up the paper

46
Q

What does an Rf value of 0 mean ?

A

The spot has not moved

47
Q

What is the mobile phase ?

A

The phase that is moving, e.g solvent or dye

48
Q

What is the stationary phase

A

The one through which the mobile phase moves, e.g the paper

49
Q

How water is made potable (3)

A
  • water is filtered through gravel and sand to remove different-sized solid particles. The gravel and sand are equivalent to different-grade filters. The gravel removes larger particles and the sand smaller particles
  • Water is treated with coagulant to Sediment any remaining, very small, solid particles and it is again filtered using a carbon filter
  • Water is finally chlorinated by adding chlorine to kill microorganisms
50
Q

Describe the process of desalination for seawater using distillation (2)

A
  • The water is evaporated and then condensed
  • Any dissolved solids do not boil and the water is separated from the dissolved sodium chloride and any other dissolved substances
51
Q

Describe the test for Cu2+, Fe2+, Fe3+, Al3+, Zn2+ and Mg2+ ions in solution using sodium hydroxide solution and ammonia solution;
(6)

A
  • Dissolve The cation in water to form a solution
  • Add a few drops of sodium hydroxide solution or ammonia solution to the test solution containing the cation
  • Observe The results
  • Continue to add the sodium hydroxide solution or ammonia solution until it is in excess
  • The colour of ppt and whether or not it redissolves in excess of either solution identifies the cation present
  • The ppt formed on addition of sodium hydroxide solution and ammonia solution is the same - it is the metal hydroxide
52
Q

Describe the tests for the following

• chloride, bromide and iodide (5)

A
  • Dissolve The sample in water to form a solution
  • Pour a few cm3 of the solution into a test tube and add a few cm3 of silver nitrate solution
  • Observe The formation of The precipitate
  • Chloride anion forms white ppt, bromide cream ppt, iodide yellow ppt
  • White ppt is silver chloride, cream ppt is silver bromide, yellow ppt is silver iodide
53
Q

Test for carbonate ions (3)

A
  • Dilute acid such as HCl is added to the solid and bubbles of gas are observed if carbonate ions are present
  • Gas is carbon dioxide
  • Bubbling this Gas through limewater results in the limewater changing from colourless to milky
54
Q

Ionic equation for the halide tests (3)

A

Ag+ + Cl- —> AgCl
Ag+ + Br- —> AgBr
Ag+ + I- —> AgI

55
Q

Why are formulated fertilisers referred to as NPK fertilisers ?

A
  • They proved plants with the correct minerals in suitable proportions for growth such as nitrogen, phosphorous and potassium compounds
56
Q

Define solute

A

A solid that dissolves is called a solute

57
Q

What is a solvent

A

The liquid in which the solute dissolves

58
Q

What is a solution

A

The resulting mixture of a solute dissolved in a solvent

59
Q

What are liquids that do not mix called ?

A

Immiscible

60
Q

What is recrystallisation ? (2)

A
  • If the solid to be obtained from evaporation contains water of crystallisation, the solution is heated to evaporate to half volume and left aside to cool and crystallise
  • The crystals form in the solution and they can be filtered off
61
Q

What is a separating funnel used to separate ?

A

Immiscible liquids based on a difference in their densities

62
Q

What is simple distillation used to separate ?

A

A solvent from a solution or one of two miscible liquids

63
Q

What happens if a liquid in the mixture for simple distillation is flammable?

A
  • a water bath or electric heating mantle is used to heat the flask rather than a Bunsen burner
64
Q

Why is simple distillation not as accurate as fractional distillation for separating water and ethanol

A
  • Some water will evaporate and the ethanol collected will not be pure
65
Q

How does the condenser in simple distillation work? (2)

A
  • Gases pass through the middle tube and cold water runs between the cylinders, providing a cold surface for the gases to condense on
  • The cooling water must go in at the bottom of the condenser and out at the top to ensure that the condenser is filled with water at all times
66
Q

Why is fractional distillation better? (2)

A
  • This method provides better separation of miscible liquids than simple distillation because evaporated liquids below their boiling point do not reach the condenser
  • they condense on the glass beads in the fractionating column and return to the flask
67
Q

What are distillates collected at different temperatures called ?

A

Fractions

68
Q

How to separate two solids - one soluble in water, the other insoluble (3)

A
  • Dissolve in water
  • filtration to obtain the insoluble solid
  • Evaporation or recrystallisation to obtain the soluble solid from the filtrate
69
Q

Examples of components separated by filtration

A

Sand and water

Sulfur and water

70
Q

Examples of components separated by simple distillation

A

Salt solution

Sugar solution

71
Q

Examples of components separated by evaporation or recrystallisation

A

Salt solution

Sugar solution

72
Q

Examples of components separated by fractional distillation

A

Ethanol and water
Crude oil
Liquid air

73
Q

When to use simple distillation ?

A

When two liquids have substantially different boiling points

74
Q

Examples of components separated by separating funnel

A

Oil and water

75
Q

Examples of components separated by chromatography

A

Dyes, food colourings, chemical indicators

Y12 Chem (16 decks)

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