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Investigative Analytical Science > Uncertainty > Flashcards

Uncertainty Flashcards

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1
Q

What is metrology?

A

Science of measurement.
Methods.
Application.

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2
Q

What is the aim of measurement?

A

To determine the numerical value of a phenomenon.

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3
Q

What are some questions we ask when we measure something?

A
  1. How much does something weight?
  2. What is the chronological age of an individual?
  3. What is the concentration of something?
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4
Q

How is a measurement characterised?

A

A comparison.

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5
Q

What does ‘ measurement is comparison’ mean?

A

If we have grams –> everything is measured in grams –> compare it in grams.

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6
Q

How are units different?

A

In length between countries.
Cities.
People.

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7
Q

What did Henry do in 12th Century?

A

Set a foot as the length of his foot.

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8
Q

When was the foot standardised across the world?

A

Only in 1959.

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9
Q

How was foot standardised?

A

‘International Yard and Pound Agreement’.

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10
Q

What are the universally accepted scales?

A

SI Systeme international units.

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11
Q

What t do we need to demonstrate based on a measurement?

A

The method we use can measure what we want to measure.
Method validation.
Calibration.

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12
Q

How is the measurement characterised when it is uncertain?

A

‘Fuzzy’.

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13
Q

What is the uncertainty of a measurement?

A

Important as measurement.

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14
Q

What do we have to reduce in our measurements?

A

Approximate measurements.

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15
Q

What is the last figure when we round it?

A

Little uncertain.

Important.

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16
Q

What is chronological age?

A

A measure.

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17
Q

What is accurate age?

A

Important.

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18
Q

Why is age important in measurements?

A

For criminal responsibility.
Legal rights.
Pension = σύνταξη.

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19
Q

Why are we unsure if months, days, hours, minutes of an individual’s birth are important in measurements?

A

Because we do not know exactly if they are correct.
Not that certain of the result.
Do not know how certain we need to be

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20
Q

What do we have if we know a person that examines was 17.5 years old, but analysis shows 16.1 - 22.3 years old?

A

Uncertainty about the true result.

Range of age.

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21
Q

What can we decide based on the experiment we do in the lab?

A

How good we wish to do it.
If it matters.
How accurate we have to be.
Behave appropriately.

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22
Q

What happens when we make a solution?

A 
We are uncertain.
Cannot express results accurately.
We are confident for values between a range.
Do it in lab.
Check how good we are.
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23
Q

What are some uncertainties we have when making a solution?

A
  1. Purity of the chemical.
  2. Weighing a chemical accurately.
  3. Calculating amount weighed out.
    Volume of solvent/liquid.
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24
Q

How do we weigh 1M NaCl?

A

Inaccurately.
~58g dissolved in ~1L water in conical flask.
Uncertainly.

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25
Q

How do measure 1.00M NaCl?

A

Accurately.
Weigh 58.4400g.
Exactly 1L of solution in volumetric flask.
Reduced uncertainty.

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26
Q

What does each glassware have?

A

Its own uncertainty.

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27
Q

What do the dots represent in plots?

A

Outliers.

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28
Q

What id cylinder as a glassware for practical sessions?

A

More precise.
Data all together in plots.
Not that accurate.

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29
Q

What glassware should we use in practical sessions?

A

Volumetric flask.

Cylinder.

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30
Q

Why should we use volumetric flask or cylinder in practical?

A

They are more precise in measurements.

Measurements closer to 100mL.

31
Q

With what will all methods of measurement come?

A

Uncertainty.

32
Q

Which are the classes of 250mL cylinder as glassware?

A

Class A +/- 0.8mL.

Class B +/- 1.4mL.

33
Q

What will Class A of cylinder glassware give in practical?

A

Uncertainty.

34
Q

What will the 250mL cylinder glassware give if used correctly?

A

250 +/- 0.8 mL.

Errors.

35
Q

Where will random errors be present in a plot?

A

At each stage of the experiment.

To all measurements.

36
Q

How do random errors happen in experiments?

A

By chance.

37
Q

What do random errors cause?

A

A symmetrical data spread round the mean.

Standard deviation on either side.

38
Q

Where are the most measurements in a plot form an experiments with random errors?

A

Within 250mL range.

39
Q

Where are the outliers in a plot with random errors?

A

At each sides.

40
Q

How is accuracy measured in a plot with random errors?

A

By standard deviation.

41
Q

What happens in a plot of precision if we do experiment again?

A

Much lower standard deviation.
Values closer to 250mL.
Better precision.

42
Q

What happens if values are more accurate?

A

More values within standard deviation.

43
Q

What does better glassware quality give us?

A

Lower standard deviation.

Greater precision of measurements.

44
Q

What happens in a plot with systematic error?

A

Lack Accuracy.
Bias in one direction.
Results are higher/lower than true value.
Measures = not true value.

45
Q

What can we do if we realise there is a systematic error in the experiment values?

A

Spike solution with known amount –> measure to see if values are the same as we have in sample.

46
Q

What can we not do to systematic errors?

A

Change them.

47
Q

What do we must do when we have systematic errors in experiment?

A

Adjust to them –> get true value.

48
Q

What does accuracy mean in an experiment?

A

How close we are to the true value.

49
Q

What does precision mean in an experiment?

A

How often we get the same value.

50
Q

What does low precision give us?

A

Large standard deviation.

Spread out data.

51
Q

What do we want to get out of an experiment?

A

High accuracy.

High precision.

52
Q

How is low accuracy and low precision out of an experiment characterised?

A

Random results.

53
Q

What is important to know in an experiment?

A

How precise we can be.

54
Q

What is gross errors?

A

Learning mechanism.

55
Q

How are gross errors caused?

A

By experimenter carelessness.

Equipment failure.

56
Q

What does learning experience mean?

A

Prepare a sample –> make a mistake –> correct it.

57
Q

What are some examples of gross errors?

A

Copying data with errors.
Incorrect labelling of solutions.
Measuring wrong sample.
Miscalculation of reagent amount required.
Confuse grams and moles.
Weighing amounts of dry sample into dirty flasks.
Meniscus going over mark.
Continuing to use solution when it is wrong.
Using solutions not dissolved.
Not shaking flask to mix contents.

58
Q

What should we do if meniscus goes over mark?

A

Wash material.

Prepare new solution.

59
Q

How should we dissolve a solution?

A

Dissolve in beaker.
Transfer in flask.
Washings.

60
Q

Why should we shake flask to mix contents?

A

Get correct amount of substances.

Correct concentrations of volume.

61
Q

What should we do in experiments to get more values and compare?

A

Get over gross errors.
Correct systematic errors.
Run measurements.
Get approximate result.

62
Q

How can we compare all values of experiment?

A

5% between each measurement.

1 st. deviation between each.

63
Q

What can we check between measurements of experiment?

A

If repeated successfully.

If got same precise values.

64
Q

What can we use to determine uncertainty in values?

A

Maths.

65
Q

Wat can we do with all the random and systematic errors?

A

Combine them.

Give overall uncertainty of result.

66
Q

How often should gross errors occur?

A

Rarely.

67
Q

How can we report uncertainty?

A

50 +/- 5 mg/100ml.

50 - 5 = 45mg/100ml ‘not less than’.

68
Q

What can we determine by using error spread?

A

Value of uncertainty.

69
Q

What should we talk about when talking about errors in practical sessions?

A

Gross errors.
Random errors.
Systematic errors.

70
Q

What should we do with gross errors?

A

Do them again.

71
Q

What are random and systematic errors?

A

Uncertainties.

72
Q

What should we identify in practical sessions?

A

Errors.

73
Q

Why should we identify errors in practical sessions?

A

To minimize uncertainty.

Investigative Analytical Science (16 decks)

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