1. Scientific Measurement
CHAPTER 3
Scientific Measurement

2. Scientific Measurement
International system of Units (SI)
Revised version of the metric system
Grams and liters not pounds and ounces
Base units
length, mass, temp, time, etc.
Derived units can be calculated
density, volume, pressure

3. Two Types of Measurements
Qualitative = descriptive and non-numerical
EX: color, odor, texture, etc
Quantitative = definite form, numbers and units
EX: temperature, mass, length, volume, density

4. Scientific notation Used to write very big and very small numbers
6.02 X 1023 instead of
Number is written as the product of 2 numbers: a coefficient and Exponent
N X 10x
N is a coefficient; a number that is between 1 and ten
X is an exponent (integer)

5. Scientific Notation rules
Coefficient: expressed as a number between 1 and 10 (not including 10)
Exponents
if the # is greater than ten, the exponent is positive
if the # is less than one, the exponent is negative
A number between 1 and ten will not be converted

6. Converting a number into scientific notation. 9 8 7 6 5 4 3 2 1
Step #1: Insert an understood decimal point
Step #2: Decide where the decimal must end
up so that one number is to its left
Step #3: Count how many places you bounce
the decimal point
The exponent is the number of places we moved the decimal.
Step #4: Re-write in the form M x 10n
2.5 X 109

7. Converting a number into scientific notation
2.5 X 109
The exponent is positive because the number we started with was greater than 10.

8. Converting a number into scientific notation1 2 3 4 5
Step #1 Locate the decimal
Step #2 Decide where the decimal must end up so that one number is to its left
Step #3 count how many places you bounce the decimal point
Step #4 Re-write in the form N x 10x

9. Converting a number into scientific notation
The exponent is negative because the number we started with was less than 1.

10. CHEM-practice… Convert the following
written as
written as
written as
4.5 x written as
3.2 x written as
2.89 x written as
4.5 x 10 4
5.3 x 10 2
6.02 x 10 5
0.032
If you moved the decimal point to the left, your exponent is positive
If you moved to the right, your exponent is negative

11. Uncertainty in measurement
Accuracy = how close a measurement comes to the actual or true value of whatever is measured
Precision = how close a series of measurements are to one another
Precise, not accurate

12. Uncertainty in measurement
Accurate, not precise

13. Uncertainty in measurement
Not precise, not accurate

14. Uncertainty in measurement
Precise AND accurate

15. Error in measurement Accepted/actual value Experimental value
the correct value based on reliable references
Experimental value
the value measured in the lab
Error = accepted – experimental
% error = I accepted – experimental I x 100
accepted

16. Calculating Error
A recipe says you should make 36 cookies but you only got 33 cookies. What is your percent error?
Percent Error = I accepted – experimental I x 100
accepted
accepted = 36
experimental = 33
Percent Error = I I x 100 36
= 8.3 % error

17. Significant figures
Numbers that include ALL digits that can be known plus a last digit that is estimated
Digits that have meaning

18. Significant figures Rules regarding zeros
Every non-zero digit is significant (567)
Zeros between non-zeros are sig (305)
Zeros in front of nonzeros are placeholders… NOT SIG ( )
Zeros following a nonzero only sig if
The come after a decimal point (3.4210)
Or a decimal follows (3420.)
3420

19. Significant figures
HOW MANY SIG FIGS??????
4.21
4.210
0.0421
42.10
42010
(3)
(4)
(3)
(4)
(4)
(6)

20. Rounding SIG FIGS
If the digit after the last sig fig is less than 5, drop all digits after the last sig fig (4 or below, let it go)
If the digit after the last sig fig is 5 or greater, round the value of the digit in the last sig place up by (5 and above, give it a shove)
1 Sig FIG 5
4.8610
2Sig FIG
4.9
3 Sig FIG
4.86

21. Rounding SIG FIGS
Round each of the following numbers to 2 SIG FIGS
4.21
4.210
0.0421
42.10
4210
42010
4.2
0.042 42
4200
42000

22. Scientific Measurement
International system of Units (SI)
Revised version of the metric system
Grams and liters not pounds and ounces
Base units
length, mass, temp, time, etc.
Derived units can be calculated
density, volume, pressure

23. DENSITY The ratio of an object’s mass to its volume
Objects with the same volumes but different masses will have different densities
The size, mass and arrangement of atoms affects a materials density
Copper atoms are smaller than aluminum atoms.
More copper atoms can fit in the cube.
Copper atoms are also heavier than aluminum atoms.
The combination of more and heavier atoms makes copper more dense than aluminum.

24. Calculating the Density of Water
How can you go about determining the density of water?
What kind of data do you need to measure?
Does a small amount of water have the same density as a large amount of water?
Do you think hot water and cold water have the same density?

25. Calculating Density Equation: Density = mass ÷ volume
Units: g/cm3 or g/ml

26. Calculating Density
A copper penny has a mass of 3.1 g and a volume of 0.35 cm3. What is the density of copper?
Equation: D = m/V
Units: g/cm3

27. Using Density to identify an unknown
A student finds a shiny piece of metal that she thinks is aluminum. In the lab, she determines that the metal has a volume of 245 cm3 and a mass of 612 g. Calculate the density. Is it aluminum? Density Al= 2.70 g/cm3
Equation: D = m/V
Units: g/cm3

28. Temperature Defined: direction of heat transfer
When two objects are in contact, heat moves from the object at the higher temperature to the object at the lower temperature

29. Temperature scales Celsius Kelvin scale
Uses two determined temperatures as reference temp
Boiling point of water = 100oC
Freezing point of water = 0 oC
Kelvin scale
Boiling point of water = 373 K
Freezing point of water = 273 K
Notice no degree sign
0 K = absolute zero or the point at which all motion stops

30. Converting between Celsius and kelvin
K = oC
Ex: convert 25 oC to K
K = 25 oC
K = 298K
oC = K
Ex: convert 0K to oC
oC = 0K - 273
oC = -273 oC