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GCSE CHEMISTRY > P2- Chemical analysis > Flashcards

P2- Chemical analysis Flashcards

(52 cards)

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1
Q

What are pure substances in chemistry?

A

Substances that contain only one type of element or compound, not mixed with any other substance

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2
Q

What are pure substances in everyday life?

A

-Substance that has had nothing added to it, so it is unadulterated and in its natural state, eg pure milk

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3
Q

What tells you how pure a substance is?

A

Melting or boiling point

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4
Q

How can you test the purity of a sample?

A

By measuring its melting or boiling point and comparing it with the melting or boiling point of the pure substance

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5
Q

What will impurities in your sample do?

A

-Lower the melting point and increase the melting range of your substance
-Increase the boiling point and may result in your sample boiling at a range of temperatures

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6
Q

What are formulations?

A

-A mixture that has been designed as a useful product
-Formulations are made by mixing the components in carefully measured quantities to ensure that the product has the required properties

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7
Q

Examples of formulations

A

Fuels, cleaning agents, paints, medicines, alloys, fertilisers and foods

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8
Q

What is chromatography?

A

A separation technique used to separate mixtures of soluble substances

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9
Q

2 types of chromatography

A

-Mobile phase
-Stationary phase

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10
Q

What is the mobile phase of chromatography?

A

-Molecules can move
-Always a liquid or gas
-Moves through the stationary phase
-The solvent

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11
Q

What is the stationary phase of chromatography?

A

-Molecules can’t move
-Can be a solid or a really thick liquid
-The absorbent paper

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12
Q

What is chromatogram?

A

-What is produced from the separation of dissolved substances
-Can be used to distinguish between pure and impure substances
-Pure substances have 1 dot on a chromatogram
-Impure substances have 2 or more dots on a chromatogram

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13
Q

What is an Rf value?

A

-The ratio between the distance travelled by the dissolved substances (the solute) and the distance travelled by the solvent
-Further through the stationary phase a substance moves, the larger the Rf value

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14
Q

Equation to work out Rf value

A

distance travelled by substance divided by distance travelled by solvent

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15
Q

Chromatography practical

A

1.Use a ruler, draw a pencil line 2 cm from the bottom short edge of the chromatography paper (origin)

  1. Mark 5 pencil spots at equal intervals across origin line. Make sure you keep at least 0.5 cm away from each edge of the paper
  2. Use glass capillary tube to put small spot of each colouring A, B, C and D on 4 of the pencil spots
  3. Use a different tube for each colouring. Use the 5th tube to put a small spot of the unknown mixture U on the fifth pencil spot
  4. Pour water into the beaker to a depth of no more than 1 cm.
  5. Clip the top short edge of the chromatography paper to the wooden spill. The top end is the end furthest from the spots.
  6. Carefully rest the wooden spill on the top edge of the beaker. The bottom edge of the paper should dip into the water solvent
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16
Q

What are 4 gas tests?

A

-Chlorine
-Hydrogen
-Oxygen
-Carbon dioxide

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17
Q

Test for Chlorine

A

Damp litmus paper is used and should become bleached and turned white

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18
Q

Test for Hydrogen

A

Place a burning splint at the opening of a test tube.
If hydrogen gas is present, it will burn rapidly with a
squeaky-pop sound.

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19
Q

Test for Oxygen

A

Place a glowing splint inside a test tube. The splint will relight in the presence of oxygen.

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20
Q

Test for Carbon dioxide

A

Calcium hydroxide (lime
water) is used. When carbon dioxide is
bubbled through or shaken with limewater, the limewater
turns cloudy.

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21
Q

What can flame tests do?

Study These Flashcards
A

Identify metal ions as compounds of some metals burn with a characteristic colour

22
Q

What colour flame does Lithium (Li+) ions burn with?

23
Q

What colour flame does Sodium (Na+) ions burn with?

24
Q

What colour flame does Potassium (K+) ions burn with?

25
What colour flame does Calcium (Ca2+) ions burn with?
Orange-red
26
What colour flame does Copper (Cu2+) ions burn with?
Green
27
Flame tests practical
1– Dip a wire loop into a sample of the solid compound being tested 2– Place the loop into the flame of the Bunsen burner Ensuring the Bunsen burner is set to a roaring blue flame 3– Observe the colour of the flame produced and record it in a table. Mixtures of ions may cause some flame colours to not be as clear
28
Metal hydroxides test
-Many metal hydroxides are insoluble and precipitate out of solution when formed. Some of these have a characteristic colour -In this test, add a few drops of sodium hydroxide solution to a solution of a compound to try and form an insoluble hydroxide -If you get a coloured insoluble hydroxide, you can often tell which metal was in the compound
29
What colour precipitate does Aluminium (Al3+) ions form?
White
30
Ionic equation for Aluminium (Al3+) ions formation
Al3+ (aq) + 3OH- (aq) -> Al(OH)3 (s)
31
What colour precipitate does Calcium (Ca2+) ions form?
White
32
Ionic equation for Calcium (Ca2+) ions formation
Ca2+ (aq) + 2OH- (aq) -> Ca(OH)2 (s)
33
What colour precipitate does Magnesium (Mg2+) ions form?
White
34
Ionic equation for Magnesium (Mg2+) ions formation
Mg2+ (aq) + 2OH- (aq) -> Mg(OH)2 (s)
35
What colour precipitate does Copper(II) (Cu2+) ions form?
Blue
36
Ionic equation for Copper(II) (Cu2+) ions formation
Cu2+ (aq) + 2OH- (aq) -> Cu(OH)2 (s)
37
What colour precipitate does Iron(II) (Fe2+) ions form?
Green
38
Ionic equations for Iron(II) (Fe2+) ions formation
Fe2+ (aq) + 2OH- (aq) -> Fe(OH)2 (s)
39
What colour precipitate does Iron(III) (Fe3+) ions form?
Brown
40
Ionic equations for Iron(III) (Fe3+) ions formation
Fe3+ (aq) + 3OH- (aq) -> Fe(OH)3 (s)
41
Testing for Carbonate Ions (CO₃² )
-Place a small volume of lime water into a test tube. In a separate test tube, add a small sample of the carbonate and a few drops of HCl (acids are a source of H ions) using a pipette -Seal test tube with a bung connected to a delivery tube; the delivery tube should be placed in the test tube containing the lime water -Bubbles of carbon dioxide gas will be produced -The lime water will turn a milky colour indicating a positive test for carbon dioxide
42
Equation for testing Carbonate ions
CO₃²- + 2H+ -> CO2 + H20
43
Testing for Sulfate Ions (SO₄² )
-Use a pipette, add a few drops of barium chloride solution to the sample followed by a few drops of HCl -A positive result for sulfate ions will produce a white precipitate.
44
Equation for testing Sulfate ions
SO₄²- + Ba2+ -> BaSO4
45
Testing for Halide Ions (I , Br , Cl )
-Use a pipette, add a few drops of dilute nitric acid to the sample followed by a few drops of silver nitrate solution -Leave it to stand and observe the colour of the precipitate formed
46
What colour precipitate does Chloride produce?
White precipitate of silver chloride
47
What colour precipitate does Bromide produce?
Cream precipitate of silver bromide
48
What colour precipitate does Iodide produce?
Yellow precipitate of silver iodide
49
What is Flame Emission Spectroscopy?
-An instrumental method of analysis -A technique used to identify metal ions in solution -The samples that are tested normally include biological fluids and tissues
50
Benefits of instrumental methods of analysis
-Rapid -Accurate -Sensitive
51
Drawbacks of instrumental methods of analysis
-Equipment is often expensive -Requires special training to use
52
How does Flame Emission Spectroscopy work?
1– Sample is heated in a flame. 2– Electrons in the metal ions are excited by the thermal energy provided from the flame and the electrons move into a higher energy level. 3– When the electrons fall back into a lower energy level, they release energy in the form of light 4– Emitted wavelengths of light are analysed instrumentally 5– To identify the metal present, its spectrum is compared with reference spectra from known metal ions

GCSE CHEMISTRY (12 decks)

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