Student Handout
Chemistry
Chapters 1 & 5
Scientific Method and Data
Management
World of Chemistry
Zumdahl
Last revision Fall 2008
1
Intro to Chemistry

Chemistry is the study of matter
and the changes that it undergoes.

Matter is anything that has mass and
takes up space.

Mass is a measurement that reflects
the amount of matter.

Weight is a measure of the amount
of matter and the effect of Earth’s
gravitational pull on that matter.
2
Practice

1.
2.
3.
4.
5.
6.
7.
8.
Determine whether or not the
following is considered matter.
Yes
No
Textbook
X
Air
X
Thoughts
X
Heat
X
Light
X
Radio waves
X
X
Magnetic fields
X
Sound
3
The Scientific Method
Is a systematic way of gathering evidence to
support ideas and theories that help explain the
natural world around us.
Steps to the Scientific Method

State the Problem
Do some research and form a hypothesis
1.
2.


A Hypothesis is a testable prediction based on research
and observations. It is what you think the answer to the
problem is.
A good way of writing a hypothesis is:
If…(a cause (independent variable))…then…(an effect
(dependent variable)).
4
3. Design and conduct an
experiment.
An experiment should have these three things to be a
proper experiment
I.


Variables are things that change. There
are always two;
The independent variable. Sometimes
called the manipulated variable. The
experimenter chooses one thing to do
differently in the experiment.
The dependent variable. Sometimes called
the measured or responding variable. This is
the data that is being gathered or recorded.
5
II.
Constants are all other things in the
experiment that are kept the same all
the time.
III. A control is a standard for
comparison. It is like a base line or
the data at time zero. You will
compare the data you gathered to it
to see how much the dependent
variable changed.
6
4. Analyze the Data


This includes making graphs and/or
calculations. Look for trends in the data.
Parts of a proper graph:
•
•
•
•
•
Use graph paper and a ruler
Title: Dependent vs. Independent
Labels including units: independent – x axis, dependent –
y axis
Appropriate scale: Data range/number of lines, round up
to a counting number
Smooth line or curve
7
5. Draw a Conclusion
A conclusion is a 5 sentence paragraph that
summarizes your investigation.
1)
2)
3)
4)
5)
Restates your hypothesis
Briefly describe your experiment.
What was the data you collected. Give
examples of your data as evidence.
What was the trend you found in the data or
what does the data mean.
Did the data trend support or reject your
hypothesis.
8
Report
your
results

You will
want to put
your
research
out for peer
review
and/or
publish your
findings for
your peers
to evaluate.
9
Review
1.
2.
3.
Try to name all 5 steps of the
scientific method in order.
What are the parts of an
experiment?
What is the difference between the
two types of variables?
10
Practice

In the following scenario try to
determine the parts of the experiment
and write a hypothesis.
Sally wanted to determine the effect the
amount of sunlight had on the
growth of tulips. She had 3 of the
same types of tulips in the same
amount of soil and pots. Pot A got
sunlight all day, Pot B got no
sunlight, and Pot C only got 2 hours.
The tulips received the same amount
of water and they began with the
same height. Sally conducted this
experiment for 1 week and measured
the height daily for all tulips.
11
Sally Experiment




Objective: To determine the effect the amount of
sunlight had on the growth of tulips.
Three Test Samples
 Pot A got sunlight all day
 Pot B got no sunlight,
 Pot C only got 2 hours of sunlight.
Constant
 the same types of tulips in the same amount of soil
and pots.
 The tulips received the same amount of water and
they began with the same height.
Duration:

Conducted this experiment for 1 week and measured the
height daily for all tulips.
12
Sally Experiment

Hypothesis

Independent variables

Dependent variables

Constant

Control
13
Types of Data


Qualitative data- information that
describes color, odor, shape, or
some other physical characteristic.
In general, anything that relates to
the 5 senses: how something looks,
feels, sounds, tastes, or smells.
Quantitative data- numerical
information gathered. It tells you
how much, how little, how big, how
tall, or how fast.
14
Practice

1.
2.
3.
4.
5.
6.
7.
8.
Determine whether the following is considered
quantitative or qualitative data.
15 mg of NaCl
Blue color
Answers:
1 mm
Quantitative- # 1, 3, 4, 7
7 m/s
Slippery feel
Malleable
2 g/mL
Salty
Qualitative- # 2, 5, 6, 8
15
Theory & Law

A theory is an explanation that has
been supported by many, many
experiments. It is the most logical
explanation of why things work they way
they do.

Scientific Law is a relationship in
nature that is supported by many
experiments. It is a rule that describes,
but doesn’t explain, a pattern in nature
and predicts what will happen under
special conditions.
16
Practice
1.
2.
What is the main
difference between a
theory and law?
Name one theory and
one law.
17
The Metric System


This system is based on powers of 10.
It consists of a base unit which is changed
by powers of ten when a prefix is added
Metric Conversion scale
Great Mighty King Henry Died Monday drinking chocolate milk maybe no one noticed
Giga __ __ Mega__ __ Kilo Hecto
G-
M-
K- H-
109
106
1000 100
Deka
D- or dk-
10
base unit deci
(meter)
m,g,L,s d1
centi milli__ __micro__ __nano__ __pico
c-
0.1 0.01
m-
µ-
n-
p-
0.001
10-6
10-9
10-12
18
SI System

Because units are combined all the time in
math equations they often become very large
and complex. They are called derived units
and consist of multiple base units. Scientists
tend to abbreviate them.
Example: The equation for potential energy is Ek= mgh
The unit for this using all base units is Kg m 2/s2
The abbreviated version of this unit is J for Joule

Without standardizing the base units,
scientists would never know which mass,
distance and time unit was imbedded in the
abbreviated unit Joule.
19
7 Standard Base Units
Quantity
Base unit
Time
Length
Mass
Temperature
Seconds (s)
meter (m)
Kilogram (Kg)
Kelvin (K)
mole (mol)
Amount of a specific
substance
Electric
current
ampere (A)
Luminous intensity
candela (cd)
20
Derived Units





A unit that is defined by a combination of base
units. Some derived units are:
volume (m3),
density (g/ml= g/cm3),
energy (J = kg*m2/s2).
Newton = Unit for force or metric for weight
like English pound.
N = kg*m
s2 (Note: These are all SI base units.)
21
Measurements and
Significant Digits

A measurement consists of three things.
1. A number: this is the value of the
measurement.
2. The number of digits in the number or
the resolution: this indicates the
smallest increment the equipment scale
read to.
3. The unit: this is a label that tells you
how the measurement was made.
22

Determine the length of the red line.
What is the value of the lines between the 2 cm and 3 cm marks?
0.1 cm
So this line is at least 2.8 cm
Is it exactly on the line? No
What would the imaginary lines between 0.8 and 0.9 be worth?
.05 cm
Since it is hard to estimate where it is between the lines just say it
is half way if it is between the lines or .05 cm, if it is on the line,
keep the decimal place but just report a zero or .00 cm.
What is the length of the red line here?
2.85 cm
23
Practice

1.
2.
3.
4.
Determine the number of
significant digits in the following.
Answers:
476
1. 3
0.00910
2. 3
8500
3. 2
1.000
4.
4
24
Significant Digits

The Atlantic/Pacific rule:
If a decimal is
absent, start
on the Atlantic
side of the
number.
If a decimal is
present, start
on the Pacific
side of the
number.
Go through all
zeros until you
hit a real
number. All
digits after that
are significant.
20815000
0.00007895 5 significant
4 significant
digits
digits
Go through all
zeros until you
hit a real
number. All
digits after that
are significant.
25
Calculations with Significant Digits
Addition & Subtraction: report you answer in
the least decimal places as your data.
13.81
.0045
25413.0013
1.7
+
25428.51
25428.5
This is the last digit but you must
calculate the next one to see if you
should round
26
Multiplication & Division: report your
answer in the least number of
significant digits as your data.
45.3 x 67.9008
3 digits
= 3075.9062
6 digits
3080
or
3.08 x103
Scientific
notation can be
used to report
the correct
number of
significant digits
You try:
6.87 + 28.1 + 570.3368 =
67.38 / 59.256 =
27
Scientific Notation





This is used to make very large and very small numbers
manageable. Ex. 4,763,000,000 = ?
Report only one digit to the left of the decimal.
Multiply by a power of 10 that you have removed from
original number.
If your number becomes smaller by moving the decimalyour exponent should be larger. Ex. 4.763 X 109 
greater than 0.
If your number becomes larger by moving the decimalyour exponent should be smaller (be careful of negative
numbers).
Ex. 0.000 007 = 7 X 10-6  smaller than 0.
28
Calculations with
Scientific Notation

When adding or subtracting numbers in
scientific notations, the exponents must
be the same.



You can adjust the position of the decimal to
make the exponents the same.
When multiplying, exponents are
added.
When dividing, exponents are
subtracted
29
Practice

1.
2.
Determine the scientific notation
for the following.Answers:
57100 =
1. 5.71 X 10 4
0.0008 =
2. 8 X 10 -4
30
% Errors in data
There are numerous types of errors that can
occur in the lab.
1. Equipment error: This happens when the equipment
used for an experiment wasn’t calibrated or is faulty.
2. The error tends to be consistent throughout the data.
This usually results in data that is precise but not
accurate.
3. Operator error: These are mistakes made by the
experimenter. It may be technique problems or
mistakes that result in regular errors occurring each
time. These results are usually neither precise nor 31
accurate.
% Errors in data



Errors can all average out to be an accurate
value by coincidence. This would not be
precise but accurate.
The best is to strive for both precision
and accuracy to achieve the best data
possible,
The best way to gather data is to take
multiple measurements (minimum of three)
of the same data and then taking an
average of the data.
32
Calculating Percent Error


The percent error calculation is used to see
how far off your experimental data is from the
theoretical, accepted, book or true value.
An acceptable variance is within 5% of the true
value.
% Error = |True value – Experimental value| x100
True value
33
Practice
Determine the percent error, if the
experimental value obtain was 1.24 g and
the accepted value was 1.30 g.
G: AV= 1.30g, EV= 1.24g
U:% Error
E: % Error = | (AV- EV) / AV | *100
S: (1.30 g – 1.24 g) = 0.06 g
 0.06 g X 100 %
1.30 g
S:
= 4.6 %
=5%

34
Dimensional Analysis
1.
Decide what conversion factor or equality you
need to use by comparing what unit you have in
the problem with the unit you are trying to
change it to and write it on your paper.


58.3 in. = ? ft
I will use 12 inches = 1 foot
Put the given value in your problem over 1.
58.3 in.
1
(Be sure the measurement has only one unit. You
can only change one unit at a time)
2.
35
Dimensional Analysis
3.
Write the conversion factor as a quotient (a fraction) so
that the unit you are changing is canceled (on the bottom
of the quotient) and the unit you want to keep is left (on the
top of the quotient).
12 in. = 1 ft.
58.3 in.
1
4.
12 in.
1 ft.
or
1 ft.
12 in.
1 ft.
12 in.
Carry out the math to solve for the desired value being sure to follow
the order of operations for math.
58.3 in.
1
1 ft.
12 in.
= 4.86 ft
36
Dimensional Analysis
5. Finally, make sure you list the new
unit with your number. If you did it
right your old unit should cancel and
the new unit will be left.
58.3 in.
1
1 ft.
= 4.86 ft.
12 in.
37
Practice
How many pizzas are needed for 3,000
people at one slice per person?
Given: 3, 000 People
Find: # of Pizza
CP: pizza  Slices
Eq: 1pizza = 8 slices
CF: 1pizza / 8 slices or 8 slices / 1pizza
S: 3,000 slices X 1 pizza = ?
8 slices
= 375 pizzas
1.
38
Practice cont’d
How many slices would be available from 25
pizzas ?
Given: 25 pizzas
Find: # of Slices
CP: pizza  Slices
Eq: 1pizza = 8 slices
CF: 1pizza / 8 slices or 8 slices / 1pizza
2.
S: 25 pizzas X 8 slices = ?
1 pizza
= 200 slices
39
Temperature conversions

The metric unit for temperature is Celsius but
the SI unit for temperature is Kelvin.
C =(o F – 32) (5/9)
O F = (o C (9/5)) + 32
K = o C + 273
O C =
K – 273
O
Note: From o F to Kelvin it is 2 steps.
40
Practice
78 ºF  ºC
 89 ºC  ºF
 47 ºC  K
 200 K  ºC
 55 ºF  ºC  K

41
Precision vs. Accuracy

Precision: a measure of how close
together a series of measurements are
to each other.

Accuracy: a measure of how close
a measurement is to the “true value”;
calculating percent error is a way to
evaluate accuracy.
42
Practice

1.
2.
3.
4.
Determine whether the data points are
precise and/or accurate, if the accepted
value is 1.3 g.
1.24 g, 1.23 g, 1.21 g Precise
1.30 g, 1.31 g, 1.29 g Both
2.0 g, 1.20 g, 1.43 g Neither
1.30 g, 1.30 g, 1.30 g Both
43
Representing Data


Graphs are used as a visual display of
the data.
Types of graphsCircle/ Pie: show parts of a fixed
whole.
Bar: show how a quantity varies with
factors such as time, location, or
temperature.
Line: used to find relationships
between two variables.
44
Graphs
Be sure to include the following when
constructing a graph.
1.
2.
3.
4.
5.
Title- Dependent variable Vs. Independent variable.
Scale- use even increments.
The origin- not always at (0,0).
Labels & units for the axes- x-axis = independent
variable & y-axis = dependent variable.
Fitting a line or curve. DO NOT connect the dots or
data points!
45
Bar & Line Graphs


Bar and line graphs are
constructed on a set of axes
 X axis runs horizontal
( →)
 Y axis runs vertical
(↑)
These axes must be labeled
properly
 The x-axis should be
labeled with the
independent variable and
unit
 The y-axis should be
labeled with the dependent
variable and unit
Y-axis
X-axis
46