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AH Chemistry > ✅ 8. Chemical Analysis > Flashcards

✅ 8. Chemical Analysis Flashcards

1
Q

What is a pure substance in chemistry?

A

A pure substance in chemistry is a single element or compound, not mixed with any other substance

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2
Q

What are the key features of a pure substance?

A

A pure substance has a specific fixed melting point and a specific fixed boiling point

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3
Q

What can we use melting and boiling points for?

A

We can use melting and boiling points to identify pure substances

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4
Q

How can we determine if a substance is pure or is a mixture?

A

By measuring its melting point and boiling point

  • If it melts and boils at different temperatures than a pure substance then it is an impure substance
  • If it metls or boils over a range of temperatures than at a single temperature then it is an impure substance
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5
Q

What is a formulation?

A
  • A formulation is a complex mixture that has been designed as a useful product
  • In a formulation, each chemical has a specific purpose
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6
Q

Describe how formulations are made?

A

Formulations are made by mixing the components in carefully measured quantities to ensure that the product has the properties we need

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7
Q

List 7 examples of formulations

A
  • Paints
  • Medicines
  • Fuels
  • Cleaning agents
  • Alloys
  • Fertilisers
  • Foods
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8
Q

INFO CARD

Paint Formulation:

A
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9
Q

Explain the use of chromotography

A

Chromotography is used to separate mixtures and can give information to help identify substances

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10
Q

How does paper chromotography separate mixtures?

A

Paper chromotography separates mixtures based on their different solubility

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11
Q

Explain the two phases of chromotography

A
  • The stationary phase does not move, so the paper is the stationary phase
  • The mobile phase is the one that moves past the stationery phase, carrying the components of the mixture with it, so the solvent is the mobile phase
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12
Q

Explain why the distance moved by each substance in the mixture differ?

A
  • Each substance in the mixture has a different attraction for the mobile and stationery phase
  • A substance that is more soluble has a stronger force of attraction between itself and the mobile phase than between itself and the stationary phase, so it will travel further up the paper
  • A substance that is less soluble has a stronger force of attraction between itself and the stationary phase than between itself and the mobile phase, so it will travel the least up the paper
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13
Q

How do we distinguish pure & impure substances on paper chromatography

A
  • A pure substance will only produce a single spot in all solvents
  • An impure substance will separate into different spots to show all the different components as separate spots
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14
Q

What is the purpose of the Rf value?

A

The purpose of the Rf value is to identify the components of mixtures by comparing it with the Rf values of known substances

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15
Q

Formula for calculating the Rf value?

A

Distance from the baseline (pencil mark)

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16
Q

How can we test for hydrogen?

A
  • To test for hydrogen, we hold a burning splint at the open end of a test tube of the gas
  • If it is hydrogen, then it will burn rapidly with a pop sound
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17
Q

How can we test for oxygen?

A
  • To test for hydrogen, we insert a glowing splint inside the test tube of gas
  • If the gas is oxygen, then the splint will relight
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18
Q

How can we test for carbon dioxide?

A
  • To test for carbon dioxide, we use limewater, which is an aqueous solution of calcium hydroxide (it is dissolved in water)
  • When carbon dioxide is shaken with or bubbled through limewater, the limewater turns milky (cloudy)
19
Q

How can we test for chlorine?

A
  • To test for chlorine, we insert damp litmus paper into the mouth of the test tube containing the gas
  • If chlorine is present, the litmus paper becomes bleached and turns white
20
Q

What can flame tests be used for?

A

Flame tests can be used to identify some metal ions (cations) through the distinctive colours produced in flame tests

21
Q

Explain how flame tests work

A
  • Dip the loop of an unreactive metal wire such as nichrome wire loop into concentrated hydrochloric acid
  • Hold it in the roaring blue flame of a Bunsen burner until there is no colour change
  • This ensures that the wire is cleaned and that there is no contamination
  • Then dip the loop into concentrated hydrochloric acid again before dipping it into the metal compound that is being tested
  • Hold the loop in the roaring blue flame of the bunsen burner
  • Use the colour of the bunsen flame to identify the metal ion present
22
Q

What do lithium compounds present in a flame test?

A

Lithium compounds result in a crimson flame

23
Q

What do sodium compounds present in a flame test?

A

Sodium compounds result in a yellow flame

24
Q

What do potassium compounds present in a flame test?

A

Potassium compounds result in a lilac flame

25
Q

What do calcium compounds present in a flame test?

A

Calcium compounds result in a orange-red flame

26
Q

What do copper compounds present in a flame test?

A

Calcium compounds result in a green flame

27
Q

Explain why the colour of the flame can be incorrect?

A

The colour of the flame can be incorrect if the nichrome wire loop was not cleaned proprely, so there were two or more ions which means the colours will mix

28
Q

What may happen to the flame tests if a mixture of ions is used

A

If a sample containing a mixture of ions is used some flame colours can be masked

29
Q

What are the two ways metal ions (cations) can be identified?

A

Metal cations can be identified through:
- Flame Tests
- Using Sodium Hydroxide Solution

30
Q

Which 3 ions produce a white precipitate in sodium hydroxide solution?

A
  • Calcium ions
  • Magnesium ions
  • Aluminium ions
31
Q

What happens when calcium, magnesium or aluminium ions react with sodium hydroxide?

A

When calcium, magnesium or aluminium ions react with sodium hydroxide, they produce a white precipitate

32
Q

How can we differentiate between aluminium, calcium and magnesium ions if they all form white precipitates in sodium hydroxide?

A
  • When we add excess sodium hydroxide, then the aluminum precipitate dissolves
  • We can then use flame tests to distinguish calcium from magnesium
33
Q

What happens when we react copper(II) ions with sodium hydroxide?

A

A blue precipitate of copper (II) hydroxide is formed

34
Q

What happens when we react Iron(II) ions with sodium hydroxide?

A

A green precipitate of Iron (II) hydroxide is formed

35
Q

What happens when we react Iron (III) ions with sodium hydroxide?

A

A brown precipitate of Iron (III) hydroxide is formed

36
Q

How can we test for carbonate ions?

A
  • We can react the carbonates with dilute acids
  • When the carbonates react with dilute acids it fizzes and produces carbon dioxide gas
  • To make sure that the gas is carbon dioxide, we bubble the gas through limewater (see test for CO2)
37
Q

How can we test for halide ions?

A
  1. First add a few drops of dilute nitric acid to the sample
  2. Then add a few drops of silver nitrate solution
  3. If a precipitate forms, then halide ions are present
38
Q

How can we identify which halide ions are present?

A

By judging the colour of the precipitate
- If the colour of the precipitate is white, then chloride ions are present
- If the colour of the precipitate is yellow, then iodide ions are present
- If the colour of the precipitate is cream, then bromine ions are present

39
Q

How can we test for sulfate ions?

A
  • Add dilute hydrochloric acid to the sample
  • The add barium chloride solution
  • If sulfate ions are present, then a white precipitate will form
40
Q

What are instrumental methods of analysis?

A

Instrumental methods use machines rather than test tube reactions to analyse substances

41
Q

What are the advantages of using advantages of instrumental methods compared with the chemical tests

A
  • They are accurate
  • They are sensitive, so they can work with very small sample sizes
  • They are rapid and faster
42
Q

What is flame emission spectroscopy?

A

Flame emission spectroscopy is an example of an instrumental method that is used to analyse metal ions in solutions

43
Q

How does Flame Emission Spectroscopy work?

A
  • A sample of the metal ion is dissolved in water to form a solution
  • The sample is put into a flame, and the light given out is passed into a machine called a spectroscope
  • The spectroscope converts the light into a line spectrum
  • Different metal ions produce different lines, forming a spectrum similar to a barcode, which can eventually be used to identify the metal ion and also the concentration of it
44
Q

How can we use Flame Emission Spectroscopy to measure the concentration of the metal ion?

A

At a higher concentration, the intensity (brightness) increases

AH Chemistry (10 decks)

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