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Pro Chem > C12 > Flashcards

C12 Flashcards

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1
Q

How do you calculate Rf values?

A

distance moved by chemical (the ink dot) / distance moved by solvent (water)

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2
Q

What can Rf values be used for?

A

Each Rf (Retention factor) value is unique, so we can use it to identify a specific substance from a database

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3
Q

Explain why different substances move different distances in chromatography

A

The different substances are attracted differently to the molecules in the paper and solvent, so they travel at different speeds/distances up the paper

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4
Q

The more soluble a substance is in the solvent during chromatography, the less/more rapidly/slowly it will move along the paper

A

The more soluble a substance is in the solvent during chromatography, the more rapidly it will move along the paper

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5
Q

Why is the lid closed during chromatography?

A

To reduce evaporation of the solvent

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6
Q

Flame tests for positive ions (results table)

A

lithium. Li. crimson
sodium. NA+. yellow
potassium. K+. lilac
calcium. Ca2+. orange/red
copper. cu2+ green

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7
Q

Explain why metal ions emit light when in a flame

A

The electrons become excited by the heat energy and jump to a higher energy level. When the electrons relax back down to a lower state, the excess energy gained is released in the form of emitted light.

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8
Q

How to carry out a flame test?

A
  • The wire should be dipped in hydrochloric acid and then heated to clean it
  • Dip into the metal compound that is being tested
  • Hold the loop in the roaring blue flame of a bunsen burner
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9
Q

How can you test for a carbonate?

A

If you add a dilute acid to a carbonate, it fizzes and produces carbon dioxide gas.

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10
Q

How can you test for halide ions?

A

First, add dilute nitric acid and then silver nitrate solution.
If a precipitate forms, there are halide ions present.

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11
Q

Test for halide ions (results table for precipitates)

A

chloride. bromide. iodine
white. cream. yellow

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12
Q

How can you test an unknown compound for sulfate ions?

A

By adding dilute hydrochloric acid, followed by barium chloride solution.
A white precipitate tells you sulfate ions are present.

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13
Q

Advantages of instrumental analysis

A
  • More accurate
  • Can work with smaller samples
  • Quicker
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14
Q

Disadvantages of instrumental analysis

A
  • Expensive
  • Equipment requires training to use
  • Requires a database to compare
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15
Q

Why do you add 2 drops of nitric acid when testing for halides?

A

To remove any carbonate ions which will affect your result by reacting with the silver nitrate solution

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16
Q

Explain why a flame test cannot be used to identify a mixture of metals

A

Flame tests can only identify a single ion

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17
Q

Explain why flame emission spectroscopy is better than a flame test

A
  • Faster
  • Works with very small sample sizes
  • More accurate
  • Can measure multiple metal ions
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18
Q

How can you identify a metal cation?

A

Reacting unknown compounds with sodium hydroxide solution can help you identify some positive ions.

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19
Q

What positive ions form white precipitates with sodium hydroxide?

A

Aluminium, calcium and magnesium

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20
Q

Explain what the test for ammonia tells you about the properties of ammonia.

A

Ammonia dissolves in water to form an alkaline solution, because it turns damp red litmus paper blue.

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21
Q

Testing for positive ions (results)

A

copper blue
iron. green
iron3+. brown

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22
Q

Name a metal ion that would produce a green flame

A

Copper (Cu2+)

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23
Q

What color flame do sodium ions produce?

A

Yellow

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24
Q

What ion produces a lilac color flame?

A

Potassium (K+)

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25
Q

What ion produces a cream precipitate when added to silver nitrate solution and dilute nitric acid?

A

Bromide (Br-)

26
Q

What does the Rf value of a dye depends on?

A
  • Solubility of the dye in the solvent
  • Attraction of the dye to the paper
27
Q

What will produce a smaller Rf value if the solvent and paper are both changed?

A

If the dye is less soluble in the new solvent and it is more attracted to the new paper

28
Q

What two ways can increase the distance between ink spots in chromotography?

A
  • Use a different solvent
  • Allow the solvent front to travel further
29
Q

What is the compound needed to identify an aluminium ion?

A

Sodium hydroxide

30
Q

If a brown precipitate forms when sodium hydroxide is added to a mystery solution, which metal ion was present?

A

Iron (III) Fe3+

31
Q

What is the correct test for sulfate ions?

A

Add barium chloride
White precipitate forms

32
Q

What happens to aluminium in excess sodium hydroxide?

A

The aluminium hydroxide precipitate dissolves to form a colorless solution

33
Q

What happens to aluminium in excess sodium hydroxide?

A

The aluminium hydroxide precipitate dissolves to form a colorless solution

34
Q

What gas is produced when a carbonate reacts with an acid?

A

Carbon dioxide

35
Q

Children often do not like taking medicine. Suggest a substance that could be added to Aquamed to increase the desire for children to take it. Give a reason for your suggestion.

A

Sugar/flavouring so it tastes better

36
Q

What do impurities do to a substance?

A
  • Lower the shelf life of substances
  • Increase the boiling point
37
Q

What are the 2 phases in chromatography?

A

Mobile phase and stationary phase

38
Q

The less/more attracted to the chromatography paper the ink is the further/lesser it will move

A

The less attracted to the chromatography paper the ink is the further it will travel

39
Q

How many chromatography spots are produced by pure samples?

A

1

40
Q

What does chromatography produce?

A

A chromatogram

41
Q

What is the apparatus required for testing chlorine?

A
  • Test tube
  • Litmus paper
42
Q

In flame tests, what piece of apparatus is used to transfer the sample to the Bunsen flame?

A

Nichrome (nickel and chromium) wire loop

43
Q

What charge do anions carry?

A

Negative

44
Q

What is the instrument used in flame emission spectroscopy?

A

A spectroscope

45
Q

What is generated by a spectroscope in a flame emission spectroscopy?

A

Line spectrum

46
Q

What does flame emission spectroscopy identify?

A

Metal ions

47
Q

What must be added to the solution before silver nitrate when testing for halides?

A

Dilute nitric acid

48
Q

Which chemical forms a white precipitate when you test for sulfate ions in solution?

A

Barium Sulfate

49
Q

What state must a splint be in when testing for hydrogen?

A

Lit

50
Q

What feature of a line spectrum provides information about the concentration of a metal ion?

A

Intensity

51
Q

What safety precautions should you take for flame tests?

A

Safety googles and hair tied back

52
Q

What is a pure substance to a chemist?

A

A pure substance is one that is made up of just one substance (one element or compound).

53
Q

Examples of pure substances

A
  • gold
  • copper wire
  • sugar
  • salt
  • hydrogen gas
  • diamond
54
Q

What are fixed points?

A

The melting and boiling point of an element or a compound

55
Q

What is a mixture?

A

A mixture consists of 2 or more different substances that are not chemically joined together

56
Q

How does the boiling and melting points of pure/impure substances differ?

A
  • Pure substances have a sharp melting/boiling point ; the temperature stays the same when a pure substance changes state
  • Impure substances like mixtures have melting and boiling points that vary ; the temperature changes slightly as an impure substance changes state
57
Q

What is a formulation?

A

A formulation is a mixture that has been designed to produce a useful product

58
Q

Examples of formulations

A

fuels, cleaning products, paints and medicines

59
Q

Why do we draw our starting line in pencil during paper chromatography?

A

If we drew the line in pen, the pen ink would move up the paper, with the solvent.

60
Q

Required Practical - Chromatography (6 marks)

A
  • Use a ruler to draw a horizontal line (2cm from the bottom) on the chromatograhpy paper
  • Mark (number of samples) spots on the pencil line of equal distance/size
  • Use a capillary tube to put a small spot of each sample on the pencil spots
  • Pour water to a beaker of depth 1cm
  • Attach the paper to a glass rod using tape, and lower the paper into the beaker
  • The water should be below the pencil line/spots and the sides of the paper should not touch the sides of the beaker

Pro Chem (15 decks)

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