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Chemistry P2 > C12 - Chemical analysis > Flashcards

C12 - Chemical analysis Flashcards

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1
Q

In chemistry what is a pure substance?

A

A single element or compound not mixed with any other substance

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2
Q

How can you use melting and boiling points to distinguish a pure substance?

A

Pure elements and compounds melt and boil at specific temperatures

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3
Q

What would the melting point of a pure substance look like in a graph?

A
  • Sharp melting point
  • Most easily seen when the temperature of a liquid is measured as it freezes
  • Horizontal line showing a sharp melting point - it is pure
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4
Q

What would the melting point of an impure substance look like in a graph?

A
  • Gradual or fall in temperature as it freezes
  • Diagonal line
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5
Q

What is a pure substance in every day language?

A

A substance thathas had nothing added to ti, unadulterated and in its natural state

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6
Q

What does an element contain?

A

Just one type of atom

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7
Q

What is a compound?

A

Contains two or more types of atom joined together

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8
Q

What is a mixture?

A

Contains two or more different substances that are not joined together

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9
Q

What can the substances making up a mixture be?

A

Elements or compounds

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10
Q

Give examples for pure element, pure compound, mixture of elements, mixture of compounds and mixture of elements and compounds

A

Pure element - oxygen
Pure compound - carbon dioxide
Mixture of elements - oxygen and helium
Mixture of compounds - alcohol and water
Mixture of elements and compounds 0 air

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11
Q

What is a formulation?

A

A mixture that has been designed as a useful product

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12
Q

What are examples of formulations?

A
  • Fuels
  • Cleaning products
  • Paints
  • Medicines
  • Alloys
  • Fertilisers
  • Foods
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13
Q

How are formulations made?

A

Mixing the components in carefully measured quantities to ensure the product has the required properties

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14
Q

What is chromatography?

A
  • Method used to separate mixtures and can be used to identify substances
  • Involves a mobile and stationary phase
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15
Q

What does separation depend on?

A

The distribution of substances between the phases

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16
Q
A
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17
Q

What is the rf value?

A

The ratio of the distance moved by a compound(centre of spot from origin) to distance moved by solvent

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18
Q

How is rf calculated?

A

Rf=distance moved by substance/distance moved by solvent

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19
Q

How can Rf values be used to identify different compounds?

A

Different compounds have different Rf values in different solvents

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20
Q

What is the mobile phase?

A

The solvent that moves through the paper with different substances

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21
Q

What is the stationary phase?

A

Contained on the paper and does not move through it

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22
Q

How can you distinguish between pure and impure substances?(2)

A
  • Pure substance produces one spot
  • Impure substance produces two or more spots
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23
Q

How would you be able to tell if two substances are the same?(2)

A
  • Produce the same number of spots with same colour
  • Spots travel the same distance up the paper(same Rf value)
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24
Q

What is the distance travelled by substance?

A

Baseline until the spot

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25
What is the distance travelled by solvent?
Baseline to solvent front
25
RP6 - investigate how paper chromatography can be difference between coloured substances (5)
1. Draw a pencil line across the chromatography paper, 1cm from the bottom 2. Use a pipette or capillary tube to add small spots of each ink to the line on the paper 3. Place the paper into a container with a suitable solvent, making sure pencil line is above water level 4. Allow the solvent to move through paper, remove paper and let it dry 5. Measure distance travelled by substance/distance travelled by solvent front and calculate rf value
26
RP6 - What is used for the stationary phase?
Chromatography paper
27
RP6 - How does chromatography work?
- Mobile phase mvoes through the stationary phase - Substance with stronger forces of attraction between itself and the mobile phase will be carried a greater distance
28
RP6 - Why is pencil used to draw a base line?
It is insoluble and so will not move during chromatography
29
RP6 - Why must the origin line be placed above water level?
So the soluble substances do not just dissolve into the water
30
RP6 - Why are different dyes separated during chromatography?
The solvent moves through the paper and different dyes have different solubilities and different attractions to the paper and so are carried at different distances
31
How do you test for oxygen?
Use a glowing splint, oxygen will relight the splint
32
How do you test for hydrogen?
Use a burning splint, hydrogen will burn rapidly(ignite) with a squeaky pop
33
How do you test for carbon dioxide?
- Aqueous solution of calcium hydroxide(lime water) used - when carbon dioxide is shaken or bubbled through it, it turns cloudy)
34
How do you test for chlorine?
- Damp litmus paper is put into chlorine gas and is bleached and turns white
35
What can flame tests be used for?
Identtify some metal ions(cations)
36
What metal ions can flame tests be used for?(5)
- Lithium - Sodium - Potassium - Calcium - Copper
37
Colour flame for lithium?
Crimson red
38
Colour flame for sodium?
Yellow
39
Colour flame for potassium?
Lilac
40
Colour flame for calcium?
Orange-red flame
41
Colour flame for copper?
Green
42
Why can you not use a flame test to identify a mixture of metal ions?
Some flame colours cna be masked by others
43
What can sodium hydroxide be used for?
Identify some metal ions
44
What metal ions can sodium hydroxide be used to identify?
Aluminium, Calcium, magnesium, copper(II), iron(II) and iron (III)
45
What happens when sodium hydroxide is added to a solution containing aluminium ions?
A white precipitate is formed, the precipitate dissolves when an excess of sodium hydroxide is added
46
What happens when sodium hydroxide is added to a solution with calcium ions?
White precipitate is formed
47
What happens when sodium hydroxide is added to a solution with magnesium ions?
A white precipitate is formed
48
What happens when sodium hydroxide is added to a solution with copper(II) ions?
Blue precipitate is formed
49
What happens when sodium hydroxide is added to a solution containing iron(II) ions?
Green precipitate is formed
50
What happens when sodium hydroxide is added to a solution with iron(III) ions?
Brown precipitate is formed
51
How can you test for carbonates?
- React with dilute acids to make carbon dioxide gas - Use limewater to identify the carbon dioxide, it will turn cloudy
52
How can carbon dioxide be identified?
With limewater, it will turn cloudy
53
How can halide ions be identified?
- Add silver nitrate - Observe colour of precipitate
54
What colour precipitate identifies bromide ions when silver nitrate is added?
Cream
55
What colour precipitate identifies chloride ions when silver nitrate is added?
White
56
What colour precipitate identifies iodide ions when silver nitrate is added?
Yellow
57
How can you test for sulfates?
- Add barium chloride and dilute hydrochloric acid - A white precipitate will form
58
RP7 - Flame test for metal ions method (6 steps)
1. Pour a small volume of chloride solution into 5 test tubes 2. Dip nichrome wire into dilute hydrochloric acid 3. Hold the tip of the wire in a Bunsen burner flame 4. Record the colour of the flame 5. Repeat for the following solutions and make sure to clean the wire after each test 6. Use the colour to identify the metal ion
59
RP7 - identify metal ions using sodium hydroxide
1. Add the metal ion solution to a test tube 2. Add sodium hydroxide in excess 3. Observe colour of precipitate formed 4. Use colour to identify the metal ions
60
RP7 - identify carbonate ions
1. Place limewater in a test tube 2. Add dilute hydrochloric acid to solution 3. Bubble through the gas produced through limewater 4. If carbon dioxide is present the limewater will turn cloudy 5. Presence of carbon dioxide indicating the solution is a carbonate
61
RP7 - identify halide ions
1. Add dilute nitric acid to test solution 2. Add silver nitrate solution 3. Observe colour of precipitate 4. Use colour to identify the ion
62
RP7 - halide ions results
- Chloride Cl- = white precipitate - Bromide F- = cream precipitate - Iodide I- = yellow precipitate
63
RP7 - identify sulphate ions
1. Add dilute hydrochloric acid to solution 2. Add barium chloride solution 3. If a white precipitate forms sulfate ions are present
64
What are instrumental methods used for?
To detect and identify elements and compounds
65
What are the 3 advantages of using instrumental methods to identify elements and compounds?
They are accurate, sensitive and rapid
66
What is flame emission spectroscopy?
- The sample is put into a flame and the light given out is passed through a spectroscope - output is a line spectrum that can be analysed to identify metal ions in the solution and measure their concentrations
67
How do you read concentrations from a flame spectroscopy?
- Solution containing ions gives a reading of ____ units on the flame photometer - you can use the calibration curve to look at the concentration

Chemistry P2 (8 decks)

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