Download chemistry-cp chapter 1 chemistry and you

CHEMISTRY-CP
CHAPTER 1
CHEMISTRY AND YOU
This chapter will introduce you to chemistry and the uses of chemistry in our
world. You will apply the scientific method to various problems and use
experiments to prove hypotheses. You will also learn the basic mathematical
skills needed to succeed in chemistry.
is also known as the central
science
• Chemists are employed in dozens of
occupations
• Whatever your career choice is,
chances are you will need some
knowledge of chemistry!!!!
The Scientific Method
Hypothesis: A Testable
Prediction
• If…then… statement
• Narrow—tests one, and only one, thing
Example 1: The static on your radio increases right before it thunders during a
storm.
Example 2: People who smoke cough more than people who don’t smoke.
Hypothesis: A Testable
Prediction
• If…then… statement
• Narrow—tests one, and only one, thing
Example 3: You sneeze every time you visit your best friend’s house.
Example 4: On a cold morning, the air pressure in the tires of your car
measures 34 psi. After several hours of high-speed driving, the pressure
measures 38 psi.
EXPERIMENT
Variable: The factor being
tested in an experiment
• Independent Variable: The
factor that you change/adjust
in the experiment
• Dependent Variable: The
factor that changes due to
changes in the independent
variable.
EXPERIMENT
Control: Factor that responds in a
predictable way to the experiment
– A control is what the rest of the experiment
can be compared to
Constant: Factor(s) that do
not change during the
experiment.
EXPERIMENT
Example: What experiment could be done to
prove/disprove the following hypothesis?
“Clean” laundry detergent causes skin rash.
•
•
•
•
Independent Variable:
Dependent Variable:
Control:
Constant:
• Data: Recorded Observations
– Qualitative:
– Quantitative:
• Graph: a visual representation of data
Graph: a visual representation of
data

x-axis: the horizontal axis


Independent Variable: The factor in the experiment
that the experimenter changes.
y-axis: the vertical axis

Dependent Variable: The factor that changes due to
changes in the independent variable.
Y-axis
x-axis
Steps to Graphing

Numbering: Make sure the numbers you put on
the axes follow patterns.


For example: 2, 4, 6, 8, 10 or 5, 10, 15, 20 or 0.1,
0.2, 0.3, 0.4 etc.
Labeling: Make sure you label each axis with a
title and a unit and that you title your graph.
Trends

Best Fit Line: A straight line that goes through
the center of most points.
Trends cont.

Inversely Proportional: As one variable
increases, the other variable decreases.
Trends in Graphing

Directly Proportional: As one variable
increases/decreases the other does the same
Example: Create a line graph of the following data:
Y-axis
x-axis
Mass (g)
Volume
(cm3)
25
100
30
115
40
134
50
160
54
163
Draw Conclusions
Theory: Explains
• States the “Why”
Law: States a Fact
• States the “What”
Base Units: The 7 metric units that
SI is built upon
Physical Quantity
Unit Name & Symbol
Measured using…
Mass
Length
Time
Quantity
Temperature
Electric Current
Ammeter
Luminous Intensity
Photometer
NON-SI UNITS
Physical Quantity
Volume
Pressure
Temperature
Energy
Unit Name
Unit Symbol
Derived Units
1. Write the mathematical formula for the
quantity.
2. Replace the formula with units and simplify.
Density
Density = Mass  Volume
METRIC CONVERSIONS
METRIC PREFIXES
PREFIX
ABBREVIATION
megakilodekaBASE UNIT
decicentimillimicronanopico-
UNIT EQUALITY
DIMENSIONAL ANALYSIS
• What is a conversion factor equal to?
• How do you use conversion factors?
DIMENSIONAL ANALYSIS
Steps to Dimensional Analysis
1. Start with what you know
(number and unit).
2. Times a line.
3. Add a conversion factor so
that units cancel and what
you are looking for is on
top of the ratio.
4. Check your answer.
Uncertainty in Measurements
Why are measurements uncertain?
 Precision of instrumentation varies
 Human error
Reading Measurements
 The number of digits you should write
when writing down a measurement
depends on the instrumentation you are
using.
 You should always include a number and
a unit when writing down a
measurement
 When determining a measurement
include all the digits you know for
certain plus 1 more digit.
Precision
 Also called reproducibility or repeatibility
 Measurements are close to each other (getting
the same measurements each time)
Accuracy
 Measurements are close to the actual
value
Graduated Cylinder
 Put the cylinder flat on the table and
read at the bottom of the miniscus
(bubble)
Triple Beam Balance
OPENER
With your partner, make the following measurements. Be sure
to make the measurements to the proper # of digits. Be
sure to include units for all measurements. Write your
answers on a sheet of paper and have Ms. Wack check
your answers. All materials are in the back of the
classroom.
 The volume of water in the 100 mL and 10
mL graduated cylinders.
 The length of the paper clip.
 The mass of a 100 mL beaker.
ROUNDING
 The first significant digit is the first nonzero
number.
 Count the appropriate # of sig figs, if the
next number is 5 or greater, round the last
number up 1. If not, do nothing.
 Examples:
2.3344(1)
1.029 (3)
0.00234(2)
SIGNIFICANT FIGURES
 The certain digits and the estimated
digit of a measurement.
 All the known digits of a
measurement and the one estimated
digit.
SIGNIFICANT FIGURES
1.
All nonzero numbers are significant.
123 = _____ sig figs
2.
All zeroes at the beginning are not significant.
0.0025 = _____ sig figs
3.
Zeroes between 2 nonzero digits are significant.
5007= ______ sig figs
4.
Zeroes at the end of a number are only significant if the number
contains a decimal point.
470 = ____ sig figs, 470.0 = ___ sig figs,
0.00470 = ____ sig figs
5.
In scientific notation, all numbers in the coefficient are significant.
2.020 x 104 = ____ sig figs
SIGNIFICANT FIGURES
Easier Rule: To count significant figures, if there is a decimal,
count all digits including and after the first non-zero number.
If there is not a decimal, start counting at the first non-zero
number but do not count zeroes at the end of the number.
3.3333 = ______ sig figs
3023 = ____ sig figs
72800 = ____ sig figs
2000.0 = ____ sig figs
0.216 = ____ sig figs
0.009030 = ____ sig figs
SIGNIFICANT FIGURES IN
CALCULATIONS
Multiplication/Division: The measurement with the smallest
number of significant figures determines how many significant
figures are allowed in the final answer.
Addition/Subtraction: The measurement with the smallest
number of decimal places determines how many decimal
places are allowed in the answer.
SIGNIFICANT FIGURES IN
CALCULATIONS
0.3287 g x 45.2 g =
125.5. kg + 52.68 kg + 2.1 kg =
0.258 mL  0.36105 mL =
68.32 ns – 1.001 ns – 0.00367 ns =
Scientific Notation

A number is written in 2 parts.



The first part is a number between 1 & 10
The second part is a power of ten
Exponent


Positive exponents represent numbers greater than 1
Negative exponents represent numbers less than 1
Scientific Notation

To convert a number to scientific notation:

Count how many places the decimal place must be moved to make the
number a number between 1 & 10 (the coefficient)





The number of spaces the decimal moved is the value of the exponent
If you moved the decimal to the right, the exponent is negative
If you moved the decimal to the left, the exponent is positive
Write: Coefficient x 10exponent
To convert a number from scientific notation to regular notation:


If the exponent is positive, move the decimal in the coefficient the number of
spaces indicated by the exponent to the right
If the exponent is negative, move the decimal in the coefficient the number
of spaces indicated by the exponent to the left.
Scientific Notation


Example 1: Express each of the following in scientific notation.
8960 =
36,000,000 =
0.00023 =
0.000 000 025 3 =
Example 2: Express each of the following numbers in regular
notation.
4.563 x 107 =
2.53 x 10-3 =
6.805 x 108 =
1.33450 x 10-7 =
Scientific Notation

A number is written in 2 parts.



The first part is a number between 1 & 10
The second part is a power of ten
Exponent


Positive exponents represent numbers greater than 1
Negative exponents represent numbers less than 1
Calculating in Scientific Notation
(Do not change the numbers out of scientific notation
when calculating)
Without
Calculator
(5.5 x 106) x (1.111 x 10-1) =
(9.896 x 10-34)  (3.311 x 10-24)
=
With Calculator
PERCENTS & PERCENT ERROR


Percents: A fraction can be written as a percent by converting it to a
decimal and then multiplying that decimal by 100 %.
 The % sign is like a unit!
 Example: If 20 students in a class of 33 students score an A on a
test, what percentage of students got an A?
Percent Error: measured value – accepted value x 100%
accepted value
 You measure the classroom temperature to be 23C. The
actual classroom temperature is 20 C. What is your percent
error?