1. Chemistry Measurement Notes
Chapter 3:
Significant Figures, Scientific Notation,
Metric Conversions

2. Measurement Units: Without units, data has no meaning….
Mass = gram (g)
Volume = cubic centimeter (cm3), Liter (L)
Length = meter (m)
Temperature= degrees Celsius (°C) or Kelvin (K)
Density= mass/ volume (g/mL or g/cm3)
Heat= Joules (J) or calories (cal)
Without units, data has no meaning….

3. Uncertainty
When reading a measurement from a device, always estimate one extra digit.
This device measures in increments of 1 degree.
We know that there is at least 3 degrees, we know there is not more than 4, we have to estimate to the tenths place
I’d say 3.8 degrees where .8 is the uncertain digit.

4. Accuracy vs. Precision
Accuracy- how close you are to the accepted value
Precision- ability to reproduce results, getting the same answer over and over
Example- a substance has a density of 3.00g/mL. In the lab, you find the density to be:
Trial g/mL, Trial g/mL, Trial g/mL. Therefore, your data is NOT accurate, but is precise.

5. Metric Conversions 3 Metric Prefixes you must know:
1 kilo = 1000 base Ex: 1 kilogram= 1000g
100 centi = 1 base Ex: 100 centimeters=1meter
1000 milli = 1 base Ex: 1000 milliliters = 1 liter.
You must also know this:
1 mL= 1 cm3
Setting up conversion factors:
Convert 45 mm to km
Convert 5 m/min to km/hr.

6. Significant Figures (Sig Figs)
All nonzero digits are significant.
Ex: has 4 sig figs
Zeros to the right of the decimal are significant, but only if there’s a sig fig before.
Ex: 2.00 has 3 sig figs has 2 sig figs.
Zeros to the left of the decimal are NOT significant.
Ex: 0.15 has 2 sig figs.
Zeros in-between digits are significant.
Ex: has 4 sig figs.

7. Sig Figs Continued
When adding/subtracting with sig figs, you must report to the least number of decimal places. used.
Ex: 12.52m m m = m but you can only use 1 decimal so 369.8m
For multiplying & dividing. Only report to fewest sig figs used.
Ex: 2.40 * 1.2 = 2.88 but can only use 2 sig figs so answer is 2.9 (rounding rules apply).

8. Scientific Notation
Scientific Notation is used to simplify very large or very small numbers.
The only digits used in S.N. are sig figs.
Ex: 1,200,000,000 is 1.2x109
Ex: is 1.2x10-5
There can only be 1 non-zero digit in front of the decimal.

9. Calculating with S.N.
When you multiply, multiply the numbers and add the exponents,
Ex: 2.0x102 x 4.0x103= 8.0x105
When you divide, divide the numbers and subtract the exponents.
Ex: 4.6x106 ÷ 2.2x104=2.3x102
For addition and subtraction, the numbers must have the same power of ten. You add/subtract the numbers and keep the same power of ten.
Ex: 4.0x x103 = 1.0x103

10. Celsius to Kelvin
0 Degrees on the Kelvin Scale is considered absolute zero- the temperature where there is no molecular motion (theoretical).
K = °C + 273
C = K -273

11. Error & Uncertainty in Measurement
Plus/Minus Notation
Used to show how much uncertainty there is in a measurement.
Ex: a leaf is 7cm ±0.5 cm. This means the leaf could be 7.4 or it could be 6.5.
Percent Error
% Error = absolute error / true value x100
Absolute error is the difference between experimental and true value.
Ex: You found the density of water to be 1.7 g/ml. True value is 1.0 g/ml. % error is .7/1.0= 70%