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IBDP Chemistry SL/HL > Unit 11: Measurement and Data Processing ; Topic 11.1 & 11.2 Uncertainty & Error > Flashcards

Unit 11: Measurement and Data Processing ; Topic 11.1 & 11.2 Uncertainty & Error Flashcards

Flashcard Main Resource: https://sites.google.com/site/ibchemistryellesmerecollege/home/topic-11---measurement-data-processing/11-1-uncertainty-error https://docs.google.com/presentation/d/1bG82pSzkzmEQNXPHAPcgOogWW42Eaiy04BkBzKLV1nw/edit#slide=id.p19

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1
Q

Qualitative data is…

A

non-numerical data obtained from an experiment. These will be observations made during an experiment.

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2
Q

Quantitative data is…

A

numerical data

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3
Q

why do random errors arise?

A

due to the limitations of the measuring apparatus.

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4
Q

what else is random errors called?

A

human error

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5
Q

how are random errors determined?

A

it is determined by the experimenter’s skill or ability to perform the experiment and read scientific measurements.

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6
Q

what should all measurements be quoted with?

A

an uncertianty

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7
Q

what does the uncertainty indicate?

A

the size of the random error

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8
Q

what is an Analogue apparatus?

A

mechanical devices that indicate the magnitude of the quantity in the form of the pointer movement

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9
Q

when using an Analogue apparatus the uncertainty on a measurement is half of the what?

A

the smallest division that you take a reading to.

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10
Q

what is a Digital Instrument?

A

The instrument which represents the measured value in the form of the digital number

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11
Q

when using a digital instrument the uncertainty on a measurement is quoted as…

A

± the smallest division

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12
Q

what is an example of uncertainty with a reading taken with a 2-decimal place electronic balance? (digital instrument)

A

2.46 ± 0.01g.

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13
Q

if a voltmeter has an analogue scale and the smallest scale division is 1 volt, what is the uncertainty from reading this scale?

A

± 0.5 volts.

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14
Q

if a voltmeter has a digital scale that reads 13.8, What is the uncertainty from reading this scale? and how was that derived?

A

The uncertainty from reading this scale is ± 0.1 volts. This is because the least significant digit is the 8.

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15
Q

what does the effects of random uncertainties mean?

A

The effects of random uncertainties should mean that the measurements taken will be distributed on either side of the mean.

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16
Q

can random uncertainties be completely eliminated?

A

The random uncertainties can never be completely eliminated but the effect of random uncertainties can be reduced.

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17
Q

How can you reduce the effect of the random uncertainties?

A

by repeating the measurements more often.

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18
Q

what is a Systematic error?

A

Systematic errors are errors that affect the accuracy of a measurement.

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19
Q

how can a systematic error be introduced into an experiment?

A

A systematic error can be introduced into an experiment due to the apparatus used or the procedure.

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20
Q

are systematic errors are always in the same direction?

A

yes

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21
Q

how can the presence of systematic errors be identified?

A

by comparison with accepted literature values for quantities.

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22
Q

what do we use to compare the experimental value with the accepted literature value?

A

percentage error

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23
Q

what is the formula for percentage error?

A

= (experimental value – accepted value/accepted value) x 100

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24
Q

how do you know if the experiment involves some systematic errors?

A

If the percentage error is greater than the percentage uncertainty due to random errors

25
Q

what happens if the percentage error is smaller than the percentage uncertainty

A

any deviation from the literature value can be explained in terms of random errors, that is, the limitations of the measuring apparatus.

26
Q

what does precision relate to?

A

reproducibility of results, meaning that multiple measurements give nearly identical values.

27
Q

what does high precision mean?

A

High precision means that repeat values are close together and close to the mean.

28
Q

what does accuracy refer to?

A

how close a measurement is to the actual value of a particular quantity.

29
Q

what is low accuracy due to?

A

Low accuracy is due to systematic errors within the experimental procedure.

30
Q

how are random errors characterized in terms of precision and accuracy?

A

Random errors are characterized by high accuracy and low precision

31
Q

how are systematic errors characterized in terms of precision and accuracy?

A

Systematic errors are characterized by high precision but low accuracy.

32
Q

The uncertainty is usually quoted to how many significant figures?

A

one

33
Q

how should the measurement be stated?

A

the measurement should be stated so that the uncertainty is in the last significant figure – no figures should be quoted after the uncertainty.

34
Q

Consider a value of 1.735 ± 0.1 obtained from an equation, The uncertainty is in this decimal place, so no figures should be quoted beyond it. This quantity should then be quoted as…

A

1.7± 0.1.

35
Q

what are the significant digits rules?

A
  • All non-zero digits are significant.
  • “Captive” zeros (zeros between non-zero digits) are significant.
  • Leading zeros (zeros on the left) are never significant.
  • Trailing zeros…
    A). Are not significant if they are place holders(left of a decimal)
    B). Are significant if they indicate a measurement (right of a decimal)
  • Exact numbers (counting numbers) have unlimited significant digits.
36
Q

what are the rules for rounding off?

A
  • If the digit to be removed:
    A) is less than 5 the preceding digits stays the same.
    B) is 5 or greater, the preceding number is increased by 1.
37
Q

how do you add and subtract significant digits?

A
  • Add up the digits by columns.
  • Round off the final answer to the same number of decimal places as the least precise number.
38
Q

how do you multiply and divide significant digits?

A
  • Multiply the values as normal.
  • Round off the final answer to the same number of significant digits as the least precise number.
39
Q

Uncertainty’s may be reported in what 2 forms?

A

absolute value, eg. 1.23 ± 0.02m or as a percentage value, eg. 1.23m ± 2%

40
Q

out of absolute and relative uncertainties which best fits with the statement “for any measuring device is the same for each measurement.”

A

Absolute Uncertainty

41
Q

Absolute Uncertainty =

A

% Uncertainty / 100 x Value

42
Q

For Example: if the final value of calculation is 23.27 ± 1%, the Absolute Uncertainty = 1/100 x 23.27 = 0.2

Therefore, final answer is…

A

23.27 ± 0.2

43
Q

Percentage / Relative Uncertainty is the measure of the uncertainty with respect to what?

A

measure of the uncertainty with respect to the magnitude of the measurement.

44
Q

how is Percentage / Relative Uncertainty expressed?

A

It is expressed as a % with 1 or 2 s.f

45
Q

Percentage Uncertainty =

A

= Absolute uncertainty / Value x 100

46
Q

When adding or subtracting measurements, we add the what uncertainty?

A

absolute

47
Q

When multiplying or dividing measurements we add the what uncertainty?

A

relative/percentage

48
Q

Eg. Calculate the absolute uncertainty when 9.78 ± 0.04 is divided by 3.349 ± 0.005 and quote the final answer to an appropriate number of significant figures.

A

Answer = 2.92 ± 0.02

49
Q

Graphs are used extensively in science to show the relationship between two variables. Graphs may be either…

A

Sketched graphs, or Drawn graphs

50
Q

sketched graphs are where…

A

the axes are labelled but there is no scale.

51
Q

drawn graphs are where…

A

the axes are labeled and have scales.

52
Q

what is the independent Variable?

A

What is changed in an experiment – what is being investigated.

53
Q

what is the dependent Variable?

A

What is measured in an experiment.

54
Q

Fill in the blanks:

The line of best fit must be a – line and pass through the – for a – relationship.

A

The line of best fit must be straight line and pass through the origin for a proportional relationship.

55
Q

The gradient (slope) gives us an idea of what?

A

how much one quantity (the dependent variable) is affected by another quantity (the independent variable).

56
Q

what happens If the gradient is large?

A

then a small change in the independent variable has a large effect on the dependent variable.

57
Q

Gradient=

A

= Change in Y / change in X

58
Q

The units of the gradient are obtained by…

A

dividing the units of the quantity on the y-axis by the units of the quantity on the x-axis.

59
Q

what do you do to determine the gradient of a curve?

A

For a curve draw a tangent and determine the gradient of the tangent.

IBDP Chemistry SL/HL (7 decks)

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