1. Chapter 2
One of the key parts of the scientific method is the ability to make measurements.
If I told you a measurement was What would be your response?

2. The metric system is the one used in science
The metric system is the one used in science. The units are called SI units-we will see that not all the units we will use are SI units.
SI base units are listed on p 34.

3. Measurements in Chemistry
Quantity Unit Symbol
length meter m
mass kilogram kg
time second s
current ampere A
temperature Kelvin K
amt. substance mole mol

4. Measurements in Chemistry Metric Prefixes
Name Symbol Multiplier
mega M
kilo k
deka da
deci d
centi c

5. Measurements in Chemistry Metric Prefixes
Name Symbol Multiplier
milli m
micro 
nano n
pico p
femto f

6. You must know the following SI prefixes:
Kilo-1000
Deci-0.1
Centi 0.01
Milli 0.001
Others will be provided.

7. Units of Measurement Common Conversion Factors Length Volume
1 m = inches
2.54 cm = 1 inch
Volume
1 liter = 1.06 qt
1 qt = liter

8. The SI base units are used to derive other units
The SI base units are used to derive other units. Some are listed on page 36. One of the common derived units is volume. The SI unit for volume is the cubic meter (V=lxwxh) m3.
This is not a very practical unit to use in the lab.

9. Volume
The most commonly used metric units for volume are the liter (L) and the milliliter (mL).
A liter is a cube 1 dm long on each side.
A milliliter is a cube 1 cm long on each side.

10. One important physical property of matter is density .
Density = mass/volume
Every substance has its own unique density.
See p 38 for a list.

11. There is some interesting info in the table.
Notice the density of ice: 0.92g/cm3
and for water 0.998g/mL
What do you think this means?

12. Since the density formula has 3 variables, 3 types of problems are possible.
D = m/V

13. 1. given mass and volume-find density
a substance has a mass of 23.2 grams and a volume of 18.5 cm3. Find its density.
2. given density and volume, find mass (g)
D = m/V so m=D x V
The density of silver is 10.5 g/cm3. Find the mass of a block of silver with a volume of 40.0cm3.

14. 3. Given the density and mass, find the volume of a substance.
D= m/V so V= m/D
Find the volume of a piece of iron that has a mass of 147grams. ( density of iron = g/cm3)

15. Dimensional Analysis
It is important to be able to convert one unit to another. We will make use of conversion factors (also known as unit factors). For example: how many grams are there in 25 kg?
What you need to know is how many grams there are in 1 kg. We know (or will know) that there are 1000g in one Kg (or 1 kg contains grams.

16. 25 kg. X 1000 g = g.
1 kg

17. Some for you to try:
a g to kg
b cm to m
c mg to kg

18. Accuracy versus Precision
Accuracy refers to the proximity of a measurement to the true value of a quantity.
Precision refers to the proximity of several measurements to each other.

19. Percent error = (measured value-accepted value) X 100
If we happen to know the true or accepted value for a measurement then we can calculate the per cent error in our measurement.
Percent error = (measured value-accepted value) X 100
accepted value

20. Every measurement has some uncertainty associated with it. See page 46
Every measurement has some uncertainty associated with it. See page 46. In every measurement there is a known or certain quantity and an estimated quantity.
In every measurement all the numbers are significant.

21. Measurements & Calculations
Many measuring instruments allow us to make an estimate of the last number in a measurement.

22. Use of Numbers
Piece of Black Paper – with rulers beside the edges

23. Use of Numbers Piece of Paper Side B – enlarged
How long is the paper to the best of your ability to measure it?

24. Use of Numbers Piece of Paper Side A – enlarged
How wide is the paper to the best of your ability to measure it?

25. Use of Numbers Exact numbers Accuracy Precision
1 dozen = 12 things for example
Accuracy
how closely measured values agree with the correct value
Precision
how closely individual measurements agree with each other

26. Use of Numbers If you measured it-it’s significant Significant figures
digits believed to be correct by the person making the measurement
If you measured it-it’s significant
Exact numbers have an infinite number of significant figures
= 1 dozen
because it is an exact number

27. Significant Figures - Rules
Use of Numbers
Significant Figures - Rules
Leading zeroes are never significant
has three significant figures
Trailing zeroes may be significant
must specify significance by how the number is written
1300 nails - counted or weighed?
Use scientific notation to remove doubt
2.40 x 103 has ? significant figures

28. Try these:
How many significant figures are present in each of the following measurements
236.5 g ______
20.4 cm _____
970 bricks _____
92.00 kg ____
miles ______

29. Use of Numbers Multiplication & Division rule Easier of the two rules
Product has the smallest number of significant figures of multipliers

30. Use of Numbers Multiplication & Division rule Easier of the two rules
Product has the smallest number of significant figures of multipliers

31. Use of Numbers Multiplication & Division rule Easier of the two rules
Product has the smallest number of significant figures of multipliers

32. Use of Numbers Addition & Subtraction rule
More subtle than the multiplication rule
Answer contains smallest decimal place of the addends.

33. Use of Numbers Addition & Subtraction rule
More subtle than the multiplication rule
Answer contains smallest decimal place of the addends.