Origins of the Elements

1
Reporting Data

• How we report data should indicate something
  about the quality of the data.
• Getting it right is extremely important when
  other people are reading and using your data.
• Nobody goes into science because they enjoy
  propagating error.

2
Significant Figures

• How many significant figures are in the following
  numbers?
• 0.004560
• 480.00
• 480
• 4.80 x 102
• 4.8 x 102

3
Propagating Significant Figures

• Addition and subtraction
• 482.46
• 6.392
• 488.852 488.85
• For scientific notation
• 3.45 x 106 34.5 x 105
• 6.82 x 105 6.82 x 105
• 1.74 x 104 0.174 x 105
• 41.494 x 105 4.15 x 106

4
Propagating Significant Figures

• Multiplication and Division
• 6.8x10-4 x 4.51x103
• 3.0668 3.1
• Log and antilog
• log 25 1.40 105.634 4.30x105

3 sig figs
3 sig figs
2 sig figs
2 sig figs
5
Significant Figures

• How many digits should be reported in a result?
• The number is NOT random.
• The number is NOT determined by how many digits
  your calculator reports.
• The number is determined by the precision of the
  value that you are reporting.

6
Significant Figures

• Example - The reading on a balance is
• 1.0560g.
• This should be reported as 1.0560g.
• This should NOT be reported as 1.056g.

• Example - The buret reads
• 40.04mL

image from http//www.csudh.edu/oliver/demos/bur
etuse/buretuse.htm
7
Types of Errors

• Systematic (determinate)
• Reproducible error usually due to bad
  experimental design or poor laboratory
  techniques.
• generally affects the accuracy of a result
• Random (indeterminate)
• Not reproducible and uncontrollable error due to
  environmental randomness.
• generally affects the precision of a result

8
Accuracy and Precision

• Accuracy is a measure of how close an
  experimental value is to the true value
• Accuracy is increased by reducing systematic
  errors.
• Precision is a measure of the reproducibility of
  an experimental result
• Better precision is obtained by reducing random
  errors.
• Precision may also be affected by systematic
  errors as well.

9
Precision vs. Accuracy
10
Improving Accuracy and Precision

• Accuracy
• Sound experimental design
• Careful and frequent calibrations
• Meticulous work
• Precision
• Multiple analyses
• Following the same procedure for each analysis
• Improved equipment

11
Reading for Next Time

• pgs. 44-50

Problems to Work on

• Chap 3 (1,2,5a-d,11)