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Chemistry IGCSE CIE Extended > 2. Experimental Techniques > Flashcards

2. Experimental Techniques Flashcards

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1
Q

What can time be measured with?

A

Time can be measured using a stopwatch or stop-clock which are usually accurate to one or two decimal places

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2
Q

What unit is used for time?

A

The units of time normally used are seconds or minutes although other units may be used for extremely slow reactions (e.g. rusting)

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3
Q

What can temperature be measured with?

A
  • Temperature is measured with a thermometer which can normally give readings to the nearest degree Celsius
  • Digital thermometers are available which are more precise than traditional thermometers
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4
Q

How do traditional thermometers work?

A

Traditional thermometers rely upon the uniform expansion and contraction of a liquid substance with temperature;

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5
Q

Is a traditional or a digital thermometer more accurate?

A

Traditional thermometers tend to be more accurate than digital thermometers which often need to be re-calibrated

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6
Q

What unit is used for temperature?

A

degrees Celsius (ºC)

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7
Q

What can mass be measured with?

A

Mass is measured using a digital balance which normally give readings to two decimal places. These must be set to zero before use

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8
Q

What unit is used for mass?

A

The standard unit of mass is kilograms (kg) but in chemistry grams (g) are most often used

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9
Q

What can the volume of a liquid be measured with?

A

The volume of a liquid can be determined using several types of apparatus, depending on the level of accuracy needed

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10
Q

What apparatus can be used for approximate volumes?

A

For approximate volumes where accuracy isn’t an important factor, measuring cylinders are used. These are graduated (have a scale so can be used to measure)

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11
Q

What is the most accurate way of measuring a fixed volume of a liquid?

A

Using a pipette

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12
Q

What is the most accurate way of measuring a variable volume of a liquid?

A

Burette

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13
Q

How can a the volume of a gas be measured?

A

The volume of a gas sometimes needs to be measured and is done by collecting it in a graduated measuring apparatus

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14
Q

What apparatus is used in measuring the volume of a gas?

A

A gas syringe

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15
Q

What determines whether the graduated cylinder is inverted or can be used upright?

A
  • A graduated cylinder inverted in water may also be used, provided the gas isn’t water-soluble
  • If the gas happens to be heavier than air and is coloured, the cylinder can be used upright
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16
Q

When is paper chromatography used?

A

This technique is used to separate substances that have different solubilities in a given solvent (e.g. different coloured inks that have been mixed to make black ink)

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17
Q

How is the paper set up?

paper chromatography

A

A pencil line is drawn on chromatography paper and spots of the sample are placed on it.

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18
Q

Why is pencil, not pen used to draw a line? (paper chromatography)

A

Pencil is used for this as ink would run into the chromatogram along with the samples

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19
Q

What is the paper lowered into?

paper chromatography

A

The paper is then lowered into the solvent container

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20
Q

What is important to remember when lowering the paper into the solvent?
(paper chromatography)

A

making sure that the pencil line sits above the level of the solvent so the samples don’t wash into the solvent container

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21
Q

How does the solvent travel up the paper?

paper chromatography

A

The solvent travels up the paper by capillary action, taking some of the coloured substances with it

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22
Q

What causes the different substances to travel at different rates and what does this from?
(paper chromatography)

A

Different substances have different solubilities so will travel at different rates, causing the substances to spread apart.

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23
Q

What correlation is there between the solubility of a substance and the distance it travels?
(paper chromatography)

A

Those substances with higher solubility will travel further than the others

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24
Q

What does paper chromatography show?

A

This will show the different components of the ink / dye

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25
Q

If substances are the same, will they produce the same chromatograms?

A

YES

If two or more substances are the same, they will produce identical chromatograms

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26
Q

What will happen to a substance during paper chromatography if it is a mixture?

A

If the substance is a mixture, it will separate on the paper to show all the different components as separate spots

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27
Q

How can you tell the difference between a pure and impure substance using paper chromatography?

A

An impure substance will show up with more than one spot, a pure substance should only show up with one spot

28
Q

What is the difference between the boiling point of pure substances and mixtures?

A
  • Pure substances melt and boil at specific and sharp temperatures
  • Mixtures have a range of melting and boiling points as they consist of different substances that melt or boil at different temperatures
29
Q

How can an unknown pure substance be identified?

A

An unknown pure substance can be identified by experimentally determining its m.p and b.p and comparing to data tables

30
Q

Why do mixtures melt over a range of temperatures?

A

Mixtures melt over a range of temperatures as they contain two or more substances

31
Q

What does a pure substance consist of?

A

A pure substance consists of only one substance and contains nothing else.

32
Q

Where and why is it important to have pure substances?

A

To have a pure substance for food and drugs is very important as impurities could be dangerous even in small amounts

33
Q

What is routinely assessed during the production of food and drugs?

A

Melting and boiling point analysis is routinely used to assess the purity of food and drugs

34
Q

What are Retention Factor (Rf) values used to identify?

A

These values are used to identify the components of mixtures

35
Q

Is the Rf value of a particular compound always the same?

A

Yes

36
Q

What does calculating Rf values allow scientists to do?

A

Calculating the Rf value allows chemists to identify unknown substances because it can be compared with Rf values of known substances under the same conditions

37
Q

How do you calculate the Rf value?

A

Retention factor = distance moved by compound ÷ distance moved by solvent

38
Q

Does the Rf value have units?

A

NO

- The Rf value is a ratio and therefore has no units

39
Q

When are locating agents used and what do they do?

paper chromatography

A

Locating agents are substances which react with the sample and produce a coloured product which is then visible

40
Q

What substances are hard to see using paper chromatography?

What is used to solve this problem?

A

invisible samples such as proteins

A locating agent

41
Q

When is the locating agent applied to the chromatogram?

A

The chromatogram is treated with the agent after the chromatography run has been carried out, making the sample runs visible to the naked eye

42
Q

What does the choice of the method of separation depend on?

A

the nature of the substances being separated

43
Q

What is one similarity between all separation methods?

A

All methods rely on there being a difference of some sort, usually in a physical property such as b.p., between the substances being separated.

44
Q

To separate mixtures of solids, what differences can be used to carry this process out?

A

Differences in density, magnetic properties, sublimation and solubility can be used

45
Q

If using a difference in solubility to separate a mixture of solids, what must be taken into account?

A

For a difference in solubility, a suitable solvent must be chosen to ensure the desired substance only dissolves in it and not other substances or impurities

46
Q

What are immiscible liquids?

A

two or more liquids which do not mix together

47
Q

How can immiscible liquids be separated?

A

Immiscible liquids can be separated using a separating funnel or by decanting (pouring carefully)

48
Q

When is filtration used?

A

Used to separate an undissolved solid from a mixture of the solid and a liquid / solution ( e.g. sand from a mixture of sand and water

49
Q

What is placed in the funnel?
(filtration)
1.

A

Filter paper is placed in a filter funnel above another beaker

50
Q
  1. What is poured into the funnel?

filtration

A

Mixture of insoluble solid and liquid is poured into the filter funnel

51
Q
  1. How does the filter paper allow filtration to be carried out?
A

Filter paper will only allow small liquid particles to pass through as the filtrate

52
Q
  1. What is left behind in the filter paper and funnel?

filtration

A

Solid particles are too large to pass through the filter paper so will stay behind as a residue

53
Q

When is crystallisation used?

A

Used to separate a dissolved solid from a solution, when the solid is much more soluble in hot solvent than in cold (e.g. copper sulphate from a solution of copper (II) sulphate in water)

54
Q
  1. What is the first step of crystallisation?
A

The solution is heated, allowing the solvent to evaporate to leave a saturated solution behind

55
Q
  1. How can you test the solution to see if it’s saturated?

crystallisation

A

Test if the solution is saturated by dipping a clean, dry, cold glass rod into the solution. If the solution is saturated, crystals will form on the glass rod

56
Q
  1. What is done with the saturated solution?

crystallisation

A

The saturated solution is allowed to cool slowly and solids will come out of the solution as the solubility decreases, and crystals will grow

57
Q
  1. How are the crystals collected?

crystallisation

A

Crystals are collected by filtering the solution

58
Q
  1. What is done with the collected crystals?

crystallisation

A

They are then washed with cold, distilled water to remove impurities and allowed to dry

59
Q

When is simple distillation used?

A

Used to separate a liquid and soluble solid from a solution (e.g. water from a solution of saltwater) or a pure liquid from a mixture of liquids

60
Q
  1. What is the first step in simple distillation?
A

The solution is heated and pure water evaporates producing a vapour which rises through the neck of the round-bottomed flask

61
Q
  1. What happens to the vapour?

fractional distillation

A

The vapour passes through the condenser, where it cools and condenses, turning into pure liquid H2O which is collected in a beaker

62
Q
  1. What happens after all the water is evaporated from the solution?
    (crystallisation)
A

After all the water is evaporated from the solution, only the solid solute will be left behind

63
Q

When is fractional distillation used?

A

Used to separate two or more liquids that are miscible (can mix) with one another (e.g. ethanol and water from a mixture of the two)

64
Q
  1. To what point is the solution heated?

F distillation

A

The solution is heated to the temperature of the substance with the lowest boiling point

65
Q
  1. Which substance will rise first and what will happen to it?
    (F distillation)
A

This substance will rise and evaporate first, and vapours will pass through a condenser, where they cool and condense, turning into a liquid that will be collected in a beaker

66
Q
  1. Once this substance is fully evaporated, what is left behind?
    (F distillation)
A

All of the substance is evaporated and collected, leaving behind the other components(s) of the mixture

Chemistry IGCSE CIE Extended (15 decks)

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