Introduction to Chemistry

1
Introduction to Chemistry

• Numbers in Chemistry

2
Significant Figure - Rules

• Any non-zero integers are always counted as
  significant figures.
• Leading zeros are those that precede all of the
  non-zero digits and are never counted as
  significant figures.
• Captive zeros are those that fall between
  non-zero digits and are always counted as
  significant figures.
• Trailing zeros are those at the end of a number
  and are only significant if the number is written
  with a decimal point.
• Exact numbers have an unlimited number of
  significant figures. (Exact numbers are those
  which are as a result of counting e.g. 3 apples
  or by definition e.g. 1.000 kg 2.205 lb).
• In scientific notation the 10x part of the number
  is never counted as significant.

3
Determine the number of Significant Figures

• 250.7
• 0.00077
• 1024
• 4.7 x 10-5
• 34000000

• 500.0
• 0.230970
• 0.03400
• 0.34030
• 26

4
Significant Figures - Calculating

• When multiplying or dividing. Limit the answer to
  the same number of significant figures that
  appear in the original data with the fewest
  number of significant figures.
• When adding or subtracting. Limit the answer to
  the same number of decimal places that appear in
  the original data with the fewest number of
  decimal places.
• Dont record a greater degree of significant
  figures or decimal places in the calculated
  answer than the weakest data will allow.
• Dont round until the entire series of
  calculations are finished.

5
Solve to the Appropriate Number of Significant
Figures

• 34.5 x 23.46
• 123/3
• 2.61 x 10-1 x 356
• 21.78 45.86
• 23.888897 - 11.2

• 6 - 3.0
• 32.559 x 34.555
• 4433 1187
• 1.2 x 4.3
• 8.08 21.98

6
Accuracy vs Precision

• Accuracy
• How close the measurement is to the actual value
• Can be true of one measurement, a group or the
  average of a group of measurements

• Precision
• How close multiple measurements are to each other
• Need multiple measurements to make comment on
  precision

7
Actual Value 6.000 m
Which set of data is the most accurate? Which
set of data is the most precise?
8
Error in Measurements

• Percent error is used to show the error in your
  measurements

9
Actual Value 6.000 m
Calculate the percent error for each data set.