Unit 2: Scientific Processes and Measurement

1
Unit 2 Scientific Processes and Measurement
2

• Science man made pursuit to understand natural
  phenomena
• Chemistry study of matter

3
Safety Resources

• Hazard Symbols
• blue health red flammability
• yellow reactivity white special
  codes
• Scale 0 to 4
• 0 no danger
• 4 extreme danger!

4
MSDS Material Safety Data Sheet

• gives important information about chemicals
• first aid, fire-fighting, properties, disposal,
  handling/storage, chemical formula

5
Scientific Method

• General set of guidelines used in an experiment

6
Hypothesis

• Testable statement based on observations can be
  disproven, but not proven

7
Which of these is a hypothesis that can be tested
through experimentation?

• A) Bacterial growth increases exponentially as
  temperature increases.
• B) A fishs ability to taste food is affected by
  the clarity of aquarium water.
• C) Tadpoles fear of carnivorous insect larvae
  increases as the tadpoles age.
• D) The number of times a dog wags its tail
  indicates how content the dog is.

8
Law

• States phenomena but does not address why?
• Examples Newtons Laws of Motion, Law of
  Conservation of Mass

9
Theory

• Broad generalization that explains a body of
  facts
• Summarizes hypotheses that have been supported
  through repeated testing

10
Qualitative Observations

• Non-numerical descriptions in an experiment
• Example Color is blue

11
Quantitative Observations

• Observations that are numerical
• Example the mass is 9.0 grams

12
Parts of an Experiment

• Independent Variable variable that is being
  changed or manipulated by YOU
• Dependent Variable variable that responds to
  your change ---- what you see
• Controlled Variables variables that you keep
  the same

13

• Control or Control Set-up used for comparison
  allows you to measure effects of manipulated
  variable
• Directly proportional when one variable goes
  up, the other also goes up
• Indirectly proportional when one variable goes
  up, the other goes down

14

• The diagram shows different setups of an
  experiment to determine how sharks find their
  prey. Which experimental setup is the control?
• A) Q
• B) R
• C) S
• D) T

15

• DRY MIX - way to remember definitions and
  graphing
• DRY dependent, responding, y-axis
• MIX manipulated, independent, x-axis

16
Nature of Measurement
Measurement - quantitative observation
consisting of 2 parts

• Part 1 - number
• Part 2 - scale (unit)
• Examples
• 20 grams
• 6.63 x 10-34 Joule seconds

17
Measuring

• Volume
• Temperature
• Mass

18
Reading the Meniscus
Always read volume from the bottom of the
meniscus. The meniscus is the curved surface of a
liquid in a narrow cylindrical container.
19
Try to avoid parallax errors.
Parallax errors arise when a meniscus or needle
is viewed from an angle rather than from
straight-on at eye level.
Correct Viewing the meniscusat eye level
Incorrect viewing the meniscusfrom an angle
20
Graduated Cylinders
The glass cylinder has etched marks to indicate
volumes, a pouring lip, and quite often, a
plastic bumper to prevent breakage.
21
Measuring Volume

• Determine the volume contained in a graduated
  cylinder by reading the bottom of the meniscus at
  eye level.
• Read the volume using all certain digits and one
  uncertain digit.

• Certain digits are determined from the
  calibration marks on the cylinder.

• The uncertain digit (the last digit of the
  reading) is estimated.

22
Use the graduations to find all certain digits
There are two unlabeled graduations below the
meniscus, and each graduation represents 1 mL, so
the certain digits of the reading are
52 mL.
23
Estimate the uncertain digit and take a reading
The meniscus is about eight tenths of the way to
the next graduation, so the final digit in the
reading is .
0.8 mL
The volume in the graduated cylinder is
52.8 mL.
24
10 mL Graduate
What is the volume of liquid in the graduate?
6
6
_ . _ _ mL
2
25
100mL graduated cylinder
What is the volume of liquid in the graduate?
5
2
7
_ _ . _ mL
26
Self Test
Examine the meniscus below and determine the
volume of liquid contained in the graduated
cylinder.
The cylinder contains
7
6
0
_ _ . _ mL
27
The Thermometer

• Determine the temperature by reading the scale
  on the thermometer at eye level.
• Read the temperature by using all certain digits
  and one uncertain digit.

• Certain digits are determined from the
  calibration marks on the thermometer.
• The uncertain digit (the last digit of the
  reading) is estimated.
• On most thermometers encountered in a general
  chemistry lab, the tenths place is the uncertain
  digit.

28
Do not allow the tip to touch the walls or the
bottom of the flask.
If the thermometer bulb touches the flask, the
temperature of the glass will be measured instead
of the temperature of the solution. Readings may
be incorrect, particularly if the flask is on a
hotplate or in an ice bath.
29
Reading the Thermometer
Determine the readings as shown below on Celsius
thermometers
8
7
4
3
5
0
_ _ . _ ?C
_ _ . _ ?C
30
Measuring Mass - The Beam Balance
Our balances have 4 beams the uncertain digit
is the thousandths place ( _ _ _ . _ _ X)
31
Balance Rules
In order to protect the balances and ensure
accurate results, a number of rules should be
followed

• Always check that the balance is level and
  zeroed before using it.
• Never weigh directly on the balance pan. Always
  use a piece of weighing paper to protect it.
• Do not weigh hot or cold objects.
• Clean up any spills around the balance
  immediately.

32
Mass and Significant Figures

• Determine the mass by reading the riders on the
  beams at eye level.
• Read the mass by using all certain digits and
  one uncertain digit.

• The uncertain digit (the last digit of the
  reading) is estimated.
• On our balances, the hundredths place is
  uncertain.

33
Determining Mass
1. Place object on pan
2. Move riders along beam, starting with the
largest, until the pointer is at the zero mark
34
Check to see that the balance scale is at zero
35
Read Mass
1
1
4
? ? ?
_ _ _ . _ _ _
36
Read Mass More Closely
1
1
4
4
9
7
_ _ _ . _ _ _
37
Uncertainty in Measurement

• A digit that must be estimated is called
  uncertain. A measurement always has some degree
  of uncertainty.

38
Why Is there Uncertainty?

• Measurements are performed with instruments
• No instrument can read to an infinite number of
  decimal places

Which of these balances has the greatest
uncertainty in measurement?
39
Precision and Accuracy

• Accuracy refers to the agreement of a particular
  value with the true value.
• Precision refers to the degree of agreement among
  several measurements made in the same manner.

Precise but not accurate
Neither accurate nor precise
Precise AND accurate
40
Rules for Counting Significant Figures - Details

• Nonzero integers always count as significant
  figures.
• 3456 has
• 4 sig figs.

41
Rules for Counting Significant Figures - Details

• Zeros
• Leading zeros do not count as
• significant figures.
• 0.0486 has
• 3 sig figs.

42
Rules for Counting Significant Figures - Details

• Zeros
• Captive zeros always count as
• significant figures.
• 16.07 has
• 4 sig figs.

43
Rules for Counting Significant Figures - Details

• Zeros
• Trailing zeros are significant only if the
  number contains a decimal point.
• 9.300 has
• 4 sig figs.

44
Rules for Counting Significant Figures - Details

• Exact numbers have an infinite number of
  significant figures.
• 1 inch 2.54 cm, exactly

45
Sig Fig Practice 1
How many significant figures in each of the
following?
1.0070 m ?
5 sig figs
17.10 kg ?
4 sig figs
100,890 L ?
5 sig figs
3.29 x 103 s ?
3 sig figs
0.0054 cm ?
2 sig figs
3,200,000 ?
2 sig figs
46
Rules for Significant Figures in Mathematical
Operations

• Multiplication and Division sig figs in the
  result equals the number in the least precise
  measurement used in the calculation.
• 6.38 x 2.0
• 12.76 ? 13 (2 sig figs)

47
Sig Fig Practice 2
Calculation
Calculator says
Answer
22.68 m2
3.24 m x 7.0 m
23 m2
100.0 g 23.7 cm3
4.22 g/cm3
4.219409283 g/cm3
0.02 cm x 2.371 cm
0.05 cm2
0.04742 cm2
710 m 3.0 s
236.6666667 m/s
240 m/s
5870 lbft
1818.2 lb x 3.23 ft
5872.786 lbft
2.9561 g/mL
2.96 g/mL
1.030 g 2.87 mL
48
Rules for Significant Figures in Mathematical
Operations

• Addition and Subtraction The number of decimal
  places in the result equals the number of decimal
  places in the least precise measurement.
• 6.8 11.934
• 18.734 ? 18.7 (3 sig figs)

49
Sig Fig Practice 3
Calculation
Calculator says
Answer
10.24 m
3.24 m 7.0 m
10.2 m
100.0 g - 23.73 g
76.3 g
76.27 g
0.02 cm 2.371 cm
2.39 cm
2.391 cm
713.1 L - 3.872 L
709.228 L
709.2 L
1821.6 lb
1818.2 lb 3.37 lb
1821.57 lb
0.160 mL
0.16 mL
2.030 mL - 1.870 mL
50
Scientific Notation
In science, we deal with some very LARGE numbers
1 mole 602000000000000000000000
In science, we deal with some very SMALL numbers
Mass of an electron 0.00000000000000000000000000
0000091 kg
51
Imagine the difficulty of calculating the mass of
1 mole of electrons!
0.000000000000000000000000000000091 kg
x 602000000000000000000000
???????????????????????????????????
52
Scientific Notation
A method of representing very large or very small
numbers in the form M x 10n

• M is a number between 1 and 10
• n is an integer

53
.
2 500 000 000
1
2
3
4
5
6
7
9
8
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
Step 4 Re-write in the form M x 10n
54
2.5 x 109
The exponent is the number of places we moved the
decimal.
55
0.0000579
1
2
3
4
5
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 M x 10n
56
5.79 x 10-5
The exponent is negative because the number we
started with was less than 1.
57
Review
Scientific notation expresses a number in the
form
M x 10n
n is an integer
1 ? M ? 10
58
Calculator instructions

• 2 x 106 is entered as 2 2nd EE 6
• EE means x 10
• If you see E on your calculator screen, it also
  means x 10

59
Try

• 2 x 1014 / 3 x 10-3 ?
• 2 x 10-34 x 3 x 1023
• 4.5 x 1023 / 5.26 x 10-14

60
The Fundamental SI Units (le Système
International, SI)
61
Metric System Prefixes (use with standard base
units)

• Kilo 103 1000 KING
• Hecta 102 100 HENRY
• Deca 101 10 DIED
• Unit 100 1 UNEXPECTEDLY
• Deci 10-1 0.1 DRINKING
• Centi 10-2 0.01 CHOCOLATE
• Milli 10-3 0.001 MILK

62
Conversion Unit Examples

• 1 L 1000 mL 1 Hm ______ m
• 1 m ____ cm 1 Dm _____ m
• 1 kg 1000 g ___ dm 1 m

63
Metric System Prefixes (use with standard base
units)

• Tera 1012 1,000,000,000,000 THE
• Giga 109 1,000,000,000 GREAT
• Mega 106 1,000,000 MIGHTY
• Kilo 103 1000 KING
• Hecta 102 100 HENRY
• Deca 101 10 DIED
• Unit 100 1 UNEXPECTEDLY
• Deci 10-1 0.1 DRINKING
• Centi 10-2 0.01 CHOCOLATE
• Milli 10-3 0.001 MILK
• Micro 10-6 0.000001 MAYBE
• Nano 10-9 0.000000001 NOT
• Pico 10-12 0.000000000001 PASTUERIZED?

64
Conversion Unit Examples

• 1 L 1000 mL 1 m ______ nm
• 1 m ____ cm 1 Dm _____ m
• 1 kg 1000 g ___ dm 1 m
• 1 Mm _____ m 1 Gb _____ byte