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Chemistry Paper 2 > C12 Chemical analysis > Flashcards

C12 Chemical analysis Flashcards

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1
Q

What is a pure substance?

A

A pure substance is one that is made up of just one substance. The substance can be either an element or a compound

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2
Q

What is a formulation?

A

A mixture that has been designed to produce a useful product

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3
Q

How to calculate retention factor (Rf)

A

distance moved by substance / distance moved by solvent

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4
Q

What is chromatography?

A
  • Used to separate pictures of substances that are soluble in the same solvent
  • The substances in the mixture get separated because more soluble substances spread further along the paper
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5
Q

How does chromatography separate a mixture?

A
  • Particles in the mixture start off in one place
  • Some are less soluble and are adsorbed onto the paper more than others, so travel less far
  • Ones which are more soluble stay in the solvent for longer and are carried further up the paper
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6
Q

What is the retention factor?

A

It is a measure of how easily the substance can be carried through the stationary phase

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7
Q

what is the solvent front?

A

The distance that the solvent moves

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8
Q

What is the difference between the melting and boiling points of pure and impure substances?

A
  • Pure substances have a very distinct melting and boiling point
  • If impurities are added, the melting point is lowered and the boiling point is raised
  • Impure substances tend to melt and boil over a range of temperatures
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9
Q

What is the melting and boiling point of pure water?

A

Melts at exactly 0 degrees and boils at exactly 100 degrees

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10
Q

How is salt used as an impurity?

A
  • If salt is added to icy roads, the ice melts at a lower temperature
  • If salt is added to water for cooking, the water boils at a higher temperature
  • A range of temperatures may occur, depending on how much salt is added
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11
Q

describe the melting point and boiling point of a mixture

A
  • Will vary, depending on the composition of the mixture
  • A mixture does not have a sharp melting point or boiling point. It changes state over a range of temperatures
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11
Q

What is the relationship between the purity and melting/boiling point of a substance?

A

The purer the compound, the smaller the deviation from the actual value of the pure substance

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12
Q

How could we check if the water in the tap was pure?

A
  1. Heat a sample of the water to boiling point
  2. Check if the boiling point is exactly 100 degrees
  3. If it is then the water is pure
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13
Q

what are some examples of formulations?

A
  • Paint
  • Fuels
  • Alloys
  • Ready meals
  • Medicines
  • Fertilisers
  • Pesticides
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14
Q

describe the meaning of formulations

A
  • A mixture made to a set recipe for a particular use
  • All components are carefully measured and then mixed together to make a formulation
  • This ensures consistency in the product
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15
Q

Why is it important that these are formulated consistently?

A

So that the product remains the same, for example paint must maintain the correct colour in each formulation

16
Q

Examples of purposeful substances added to formulations

A

Every substance included in a formulation has a purpose, for example:
- Medicines are often coated in sugar to make them taste better while swallowing
- Cleaning agents or fuels may have chemicals added to make them taste or smell bad so that they aren’t consumed
- Fuels may be formulated to be easy to store or be easier to burn

17
Q

What is an active ingredient in formula?

A

The ingredient that delivers the effect e.g. the medicine product

18
Q

Why might tablets contain an inactive ingredients?

A
  • Preservatives, to change the taste, to allow the body to absorb the medicine more effectively
  • Cannot sell the small amount of active ingredient on its own, carrier/increase size, filler materials
19
Q

Why do tins of the same colour paint need to have the same ingredients?

A

Because otherwise the colour would be different

20
Q

How can melting and boiling points be used to check if a substance is pure?

A

Melting point and boiling point can be checked against published values - they should match, if not, the substance is impure

21
Q

what is the test for hydrogen?

A

How to carry out the test: React a metal compound (metal must be more reactive than hydrogen) with hydrochloric acid inside a test tube. Insert a lit splint into the test tube.
Positive result: The lighted splint produces a ‘pop’ sound

22
Q

what is the test for oxygen?

A

How to carry out the test: Hydrogen peroxide naturally decomposes to form oxygen and water. Reaction is sped up using the catalyst, manganese(IV) oxide inside a test tube. Insert glowing splint into the test tube.
Positive result: The glowing splint relights

23
Q

what is the test for carbon dioxide?

A

How to carry out the test: React calcium carbonate with hydrochloric acid inside a test tube, to form calcium chloride, water and carbon dioxide. Bubble carbon dioxide gas through limewater
Positive result: Limewater turns cloudy

24
Q

what is the test for chlorine?

A

How to carry out the test: Hold damp blue litmus paper near the gas
Positive result: The litmus paper will be bleached white

25
Q

Flame tests - ions and the colour flame they produce

A

Lithium (Li+) - Crimson
Sodium (Na+) - Yellow
Potassium (K+) - Lilac
Calcium (Ca2+) - Orange-red
Copper (Cu2+) - Green

26
Q

What type of charge do metal ions have?

A

Positive

27
Q

What is a precipitate?

A

An insoluble solid formed from a solution

28
Q

How can precipitates be removed from a liquid?

A

Filtration

29
Q

describe the flame test method

A
  • A nichrome wire loop should be dipped in dilute hydrochloric acid and then heated to clean it first
  • Then it should be dipped in the acid again before dipping it into the metal compound that is being tested
  • Then hold the loop in the roaring blue flame of a Bunsen burner
  • Use the colour of the bunsen flame to identify the metal ion in the compound
  • However, if the sample being tested contains a mixture of metal ions, then some flame colours can be masked. For example, the intense yellow colour of sodium ions can dominate other colours
30
Q

Coloured precipitates with sodium hydroxide

A
  • Copper (II) ions, a blue precipitate appears
  • Iron (II) ions, a green precipitate is produced
  • Iron (III) ions, a brown precipitate is formed
31
Q

How to identify halide ions

A
  • Add dilute nitric acid and then silver nitrate solution
  • If a precipitate forms, there are halide ions present
32
Q

Why is nitric acid added when identifying halide ions?

A

To dissolve the compound and to remove any carbonate ions, as they would also form a precipitate with the silver ions and therefore interfere with the test

33
Q

Coloured precipitates of halide ions

A
  • Iodide ions (I-) give a yellow precipitate
  • Bromide ions (Br-) give a cream precipitate
  • Chloride ions (Cl-) give a white precipitate
34
Q

How to identify sulfate ions

A
  • Add dilute hydrochloric acid, followed by barium chloride solution
  • If it is a positive result a white precipitate is formed with barium sulfate
35
Q

Why is dilute hydrochloric acid added when trying to identify sulfate ions?

A

To remove carbonate ions that would form a precipitate with the barium ions

36
Q

What does the formulation for paint usually contain?

A
  • A pigment, to provide colour
  • A binder, to help the paint attach itself to an object and to form a protective film when dry
  • A solvent, to help the pigment and binder spread well during painting by thinning them out
37
Q

what is flame emission spectroscopy?

A

an instrumental method used to analyse metal ions in solutions to identify the metal ions and measure their concentrations

38
Q

what are cations and anions?

A

cations are positive ions, anions are negative ions

Chemistry Paper 2 (9 decks)

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