1. Chapter 3

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?
The metric system is the one used in science. The units are called SI units.
SI base units are listed on page 74.

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. Some metric prefixes are listed on page 75.
You must know the following prefixes:
Kilo = 1000
Deci = 0.1
Centi = 0.01
Milli = 0.001

5. 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

6. The SI base units are used to derive other units
The SI base units are used to derive other units. One of the common derived units is used to measure volume. The SI unit for volume is the cubic meter. This is not a very practical unit to use in the lab because it is so large.

7. One important physical property of matter is density.
Density = mass/volume
Every substance has its own unique density.
See page 81 for a list.

8. There is some interesting info in the table.
Notice the density of ice is 0.92g/cm3 and for water it’s 0.998g/ml.
Does this difference have any significance?
Since the density formula has 3 variables, three types of problems are possible.
D = m/v

9. 1. Given mass and volume, find density
A substance has a mass of 28.4 grams and a volume of 20.5cm3. Find its density.
2. given density and volume, find mass (g).
D = m/v so m= D x v
The density of silver is 10.5g/cm3. Find the mass of a block of silver with a volume of 45.0cm3.

10. 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 147 g.

11. Dimensional Analysis
It is important to be able to convert one unit into another. We will make use of conversion factors (also known as unit factors). For example how many grams are there in 2.5Kg?
What you need to know is how many grams are in 1 Kg. We know that there are 1000 g in 1 Kg.
2.5 Kg x 1000/1Kg = 2500g.

12. Some for you to try:
a g to Kg
b cm to m
c mg to Kg

13. Accuracy and precision
Accuracy refers to the proximity of a measurement to the true or accepted valueof a quantity.
Precision refers to the proximity of several measurements of the same thing to each other.
See p64 for examples.

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

15. Every measurement has some uncertainty associated with it. See page 66
Every measurement has some uncertainty associated with it. See page 66. In every measurement there is a known or certain quantity and an estimated quantity.
In every measurement all the numbers are significant.
Many measuring instruments allow us to make an estimate of the last number in a measurement.

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

17. Use of Numbers Significant figures
digits believed to be correct by the person making the measurement
Measure a mile with a 6 inch ruler vs. surveying equipment
Exact numbers have an infinite number of significant figures
= 1 dozen
because it is an exact number

18. 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

19. How many significant figures are present in each of the following measurements.
20.4 cm
970 bricks
92.00Kg
miles

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

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

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

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

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

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