1. Chapter 1
Measurements

2. 1.1 Units of Measurement In chemistry we measure quantities.
do experiments.
calculate results.
use numbers to report measurements.
compare results to standards.
In a measurement
a measuring tool is used to compare some dimension of an object to a standard.

3. 1.1 Units of Measurement
The metric system or SI (international system) is
a decimal system based on 10.
used in most of the world.
used everywhere by scientists.

4. Volume Measurement Volume is the space occupied by a substance.
uses the unit liter (L) in the metric system.
uses the unit m3 (cubic meter) in the SI system.
is measured using a graduated cylinder.

5. Measuring Mass Mass: Amount of matter in an object
Weight: Measures the force with which gravity pulls on an object.
is measured on a balance.
uses the unit gram (g) in the metric system.
uses the unit kilogram (kg) in the SI system.

6. Temperature Measurement
The temperature of a substance
indicates how hot or cold it is.
is measured on the Celsius (C) scale in the metric system.
on this thermometer is 18 ºC or 64 ºF.
in the SI system uses the Kelvin (K) scale.

7. 1.1 Units in the Metric System
In the metric and SI systems, one unit is used for each type of measurement:
Measurement Metric SI
Length meter (m) meter (m)
Volume liter (L) cubic meter (m3)
Mass gram (g) kilogram (kg)
Time second (s) second (s)
Temperature Celsius (C) Kelvin (K)
All other units are derived from these fundamental units

8. Scientific Notation Scientific Notation
is used to write very large or very small numbers.
for the width of a human hair of m is written 8 x 10-6 m.
of a large number such as s is written 4.5 x 106 s.

9. Numbers in Scientific Notation
A number written in scientific notation contains a
Coefficient (between 0 and 10)
power of 10.
Examples:
coefficient power of ten coefficient power of ten
x x

10. Writing Numbers in Scientific Notation
To write a number in scientific notation,
move the decimal point to give a number 1-9.
show the spaces moved as a power of 10.
Examples:
= x = x 10-3
4 spaces left spaces right

11. Comparing Numbers in Standard and Scientific Notation
Here are some numbers written in standard format and in scientific notation. Number in Number in Standard Format Scientific Notation Diameter of the Earth m 1.28 x 107 m Mass of a typical human 68 kg 6.8 x 101 kg Length of a pox virus cm 3 x 10-5 cm

12. Examples Select the correct scientific notation for each.
1) 8 x 106 m, 2) 8 x 10-6 m, 3) 0.8 x 10-5 m
B g
1) 7.2 x 104 g, 2) 72 x 103 g, 3) 7.2 x 10-4 g

13. Examples
Write each as a standard number. A. 2.0 x 10-2 L 1) 200 L, 2) L, 3) L B. 1.8 x 105 g 1) g, 2) g, 3) g

14. 1.4 Accuracy, Precision, and Significant Figures
Significant figures: The number of meaningful digits in a measured or calculated quantity. They come from uncertainty in any measurement.
Generally the last digit in a reported measurement is uncertain (estimated).
Exact numbers and relationships (7 days in a week, 30 students in a class, etc.) effectively have an infinite number of significant figures.

15. Known & Estimated Digits
If the length is reported as 3.26 cm,
the digits 3 and 2 are certain (known).
the final digit, 6, is estimated (uncertain).
all three digits (2, 7, and 6) are significant, including the estimated digit.

16. Examples
. l l l l l cm
What is the length of the line?
1) cm
2) cm
3) cm

17. Examples
Classify each of the following as (1) exact or (2) measured numbers. A.__Gold melts at 1064 °C. B.__1 yard = 3 feet C.__The diameter of a red blood cell is 6 x 10-4 cm. D.__There are 6 hats on the shelf. E.__A can of soda contains 355 mL of soda.

18. Accuracy, Precision, and Significant Figures
Rules for counting significant figures (left-to-right):
Zeros in the middle of a number are like any other digit; they are always significant.
4.803 cm 4 sf
2. Rules for counting significant figures (left-to- right):
Zero at the beginning of a number are not significant (placeholders).
g 3 sf or 6.61 x 10-3 g

19. Accuracy, Precision, and Significant Figures
Rules for counting significant figures (left-to-right):
3. Zeros at the end of a number and after the decimal point are always significant.
K sf
4. Zeros at the end of a number and after the decimal point may or may not be significant.
34, ? SF

20. Rounding Numbers
If the first digit you remove is 4 or less, it and all following digits are dropped from the number = (4 s.f) If the digit you remove is 5 or greater, the last digit of the number is increases by = (4 s.f)
Books sometimes use different rules for this one.

21. Adding Significant Zeros
Sometimes, a calculator displays a small whole number. To give an answer with the correct number of significant figures, significant zeros may need to be written after the calculator result.
E.g ÷ = 
3 s.f s.f calculator zeros are needed
result to give 3 s.f

22. Examples
Round off or add zeros to the following calculated answers to give three significant figures. A cm B g C. 8.2 L

23. Examples
State the number of significant figures in each of the following measurements.
A m
B L
C g
D m

24. Multiplication and Division
When multiplying or dividing
the final answer must have the same number of significant figures as the measurement with the fewest significant figures.
Example:
x = = (rounded)
4 SF SF calculator SF

25. Addition and Subtraction
When adding or subtracting
the final answer must have the same number of decimal places as the measurement with the fewest decimal places.
one decimal place
two decimal places
calculated answer
final answer with one decimal place

26. Examples Select the answer with the correct number of
significant figures.
A x =
1) ) )
B ÷ =
1) ) ) 60
C x =
x 0.060
1) ) )

27. Examples
For each calculation, round off the calculated answer to give a final answer with the correct number of significant figures. A = 1) 257 2) ) B = 1) ) ) 40.7

28. 1.5 Prefixes
A prefix
in front of a unit increases or decreases the size of that unit.
makes units larger or smaller than the initial unit by one or more factors of 10.
indicates a numerical value.
prefix = value
1 kilometer = meters
1 kilogram = grams

29. Metric and SI Prefixes

30. Examples
Indicate the unit that matches the description. 1. A mass that is 1000 times greater than 1 gram. 1) kilogram 2) milligram 3) megagram 2. A length that is 1/100 of 1 meter. 1) decimeter 2) centimeter 3) millimeter 3. A unit of time that is 1/1000 of a second. 1) nanosecond 2) microsecond 3) millisecond