1. Scientific Measurement

2. Measurement
A measurement is a quantity that has both a number & a unit.
Examples: 67, 154, & 70 are just numbers.
67 inches, 154 pounds, & 70 miles per hour, are measurements!

3. Precision vs. Accuracy
Precision: the ability to reproduce the same value in a measurement. In other words, how repeatable measurements are.
Accuracy: The agreement between a measured value & the true value. In other words, how close a measurement comes to the actual value (the target).
Precise does not always mean accurate.

4. Precision vs. Accuracy cont.

5. Significant Figures/Digits
Significant Figures are all the digits in a number that are known & the last digit that is estimated.
They determine where to round off a calculation.

6. Significant Figures Rules:
Non-zero numbers are always significant.
Zeros between digits are always significant.
Initial zeros are not significant. (Example: has only 1 sf.)
Zeros at the end of the number are significant IF there is a decimal point.(24.0 cm has 3 sf)

7. Scientific Notation
Purpose: to express very large or very small values easily.
Ex. 1,000 = 1 x = 1 x 10-3
To convert-
Move the decimal point until there is only one digit (number) before the decimal point.
The number of moves = the exponent
Move to the left = positive exponent
Move to the right = negative exponent

8. Scientific Notation cont.
Let your calculator do the work (use the EE (or exp) button)
Examples:
5,280 = 3 moves to the left so, 5.28 x103
= 2 moves to the right so, 8.99 x 10-2

9. SI Units There are two types of units:
fundamental (or base) units;
derived units.
There are 7 base units in the SI system.
- We only use 4-5

10. Metric System Quantity Unit Symbol Mass* Gram g Length* Meter m Time*
Second s
Temperature*
Kelvin K
Amount*
Mole
mol

11. SI Units

12. Metric Table M k H da d c m u mega kilo hecto deca Base Unit deci
centi
milli
micro M k H da d c m u
1,000,000
1,000
100 10
Gram g
Liter L
Length m
0.1
0.01
0.001
1.0 x106
1.0 x103
1.0 x 102
1.0 x101
1.0x10-1
1.0x10-2
1.0x10-3
1.0x10-6

13. Derived Units
Derived Unit is a combination of other units to reach a measurement. There are 2 common derived units we will use.
Volume = cm3 or m3 = formula (L x W x H)
Density = g/cm3 = from formula (D = m/v)

14. Volume The units for volume are given by (units of length)3.
SI unit for volume is 1 m3.
Common: 1 mL=1 cm3.
Other volume units:
1 L = 1 dm3 = 1000 cm3 = 1000mL.

15. Volume

16. Density A physical property. Defined as mass divided by volume:
Units: g/cm3 or g/mL
Originally based on mass (density was defined as the mass/vol. of 1.00 g of pure water).

17. SI Units Temperature There are three temperature scales:
1. Kelvin Scale
Used in science.
Same temperature increment as Celsius scale.
Lowest temperature possible (absolute zero) is zero Kelvin.
Absolute zero: 0 K = -273 oC.

18. Temperature 2. Celsius Scale 3. Fahrenheit Scale Also used in science.
Water freezes at 0 oC and boils at 100 oC.
To convert: K = oC
3. Fahrenheit Scale
Not generally used in science.
Water freezes at 32 oF and boils at 212 oF.
To convert: Look up the formula – then forget it.

19. Temperature Scales
Know MP and BP of water in all three.

20. What the Heck is a Mole?
Atoms & molecules are too tiny & numerous to count. (Imagine counting grains of sand!) It is much easier to weigh atoms & molecules. Chemists use a mole to represent a specified number of particles. One mole of an element =6.02 x 1023 = the atomic mass. (See periodic table)
Kind of like a dozen = 12.
Except a mole = 6.02 x 1023

21. Dimensional Analysis
Method of calculation utilizing a knowledge of units.
Conversion factors are simple ratios (fractions):

22. Using a Conversion Factor
Example: convert a length of 3.25 meters to length in centimeters:
Solution: Given x Conv. = Ans.
factor
3.25 meters x 100 cm = cm
1 m

23. Using Two or More Conversion Factors
Example to convert length in meters to length in inches:
3.00 meters x 100 cm x 1 inch = in
1 m cm
This takes practice. Be patient.

24. Percent Error – used to compare data (observed values) to accepted/true values in a meaningful way
│ Obs – Acc│ x = % error
Acc