CHEMISTRY-CP CHAPTER 3 SCIENTIFIC MEASUREMENT In this chapter, you will apply the scientific method...
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Transcript of CHEMISTRY-CP CHAPTER 3 SCIENTIFIC MEASUREMENT In this chapter, you will apply the scientific method...
CHEMISTRY-CPCHAPTER 3
SCIENTIFIC MEASUREMENT
In this chapter, 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.
Example: What experiment could be done to prove/disprove the following hypothesis?
“Clean” laundry detergent causes skin rash.
• Independent Variable:• Dependent Variable:• Control:• Constant:
EXPERIMENT
• Data: Recorded Observations– Qualitative:
– Quantitative:
• Graph: a visual representation of data
Graph: a visual Graph: a visual representation of datarepresentation of data
x-axis: the horizontal axisx-axis: the horizontal axis Independent Variable: The factor in the Independent Variable: The factor in the
experiment that the experimenter experiment that the experimenter changes.changes.
y-axis: the vertical axisy-axis: the vertical axis Dependent Variable: The factor that Dependent Variable: The factor that
changes due to changes in the changes due to changes in the independent variable.independent variable.
TABLETABLE
Independent Variable Dependent Independent Variable Dependent VariableVariable
Should have at
least 3 pieces of
data!
Y-a
xis
x-axis
Steps to GraphingSteps to Graphing
Numbering: Make sure the numbers Numbering: Make sure the numbers you put on the axes follow patterns.you put on the axes follow patterns. For example: 2, 4, 6, 8, 10 or 5, 10, 15, For example: 2, 4, 6, 8, 10 or 5, 10, 15,
20 or 0.1, 0.2, 0.3, 0.4 etc.20 or 0.1, 0.2, 0.3, 0.4 etc. Labeling: Make sure you label each Labeling: Make sure you label each
axis with a title and a unit and that axis with a title and a unit and that you title your graph.you title your graph.
TrendsTrends
Best Fit Line: A straight line that Best Fit Line: A straight line that goes through the center of most goes through the center of most points.points.
Trends cont.Trends cont.
Inversely Proportional: As one Inversely Proportional: As one variable increases, the other variable increases, the other variable decreases.variable decreases.
Trends in GraphingTrends in Graphing
Directly Proportional: As one Directly Proportional: As one variable increases/decreases the variable increases/decreases the other does the sameother does the same
Y-a
xis
x-axis
Example: Create a line graph of the following data: Mass (g)Mass (g) Volume Volume (cm(cm33))
2525 100100
3030 115115
4040 134134
5050 160160
5454 163163
Draw Conclusions
Theory: Explains
• States the “Why”
Law: States a Fact
• States the “What”
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.
Graduated Cylinder
Put the cylinder flat on the table and read at the bottom of the miniscus (bubble)
Ruler
Thermometer
Significant Figures
All the digits you know for certain in a measurement + 1 more digit
What is the difference between precision & accuracy?
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
PERCENT ERROR
Percent Error: |measured value – accepted value| x 100%
accepted value
You measure the classroom temperature to be 23C. The actual classroom temperature is 20 C. What is your percent error?
ROUNDING
If the next number is 5 or greater, round the last number up 1. If not, do nothing.
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
With Calculator
(5.5 x 106) x (1.111 x 10-1) =
(9.896 x 10-34) (3.311 x 10-24) =
Significant Figures
All the digits you know for certain in a measurement + 1 more digit
Significant figures reveal the precision of a measurement and the measuring device
SIGNIFICANT FIGURESTo 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.
123 = _____ sig figs0.0025 = _____ sig figs5007= ______ sig figs470 = ___ sig figs470.0 = ___ sig figs 0.00470 = ____ sig figs2.020 x 104 = ____ sig figs
ROUNDING The first significant digit is the first nonzero number.
In a number without a decimal, zeroes at the end are not significant and therefore can be added as placeholders
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)
5060 (2)
213488 (2)
SIGNIFICANT FIGURES IN CALCULATIONSMultiplication/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 =
What do the countries in red have in common?
International System of Units (SI Units) A revised version of the metric system that
was developed in France in 1795 and was adopted by international agreement in 1960
There are 7 base SI units All other SI Units are DERIVED from the 7 base
units
Base Units: The 7 metric units that SI is built upon
Physical Quantity
Unit Name Unit Symbol Measured using…
Mass Kilogram kg Balance
Length Meter m Meterstick/Ruler
Time Second s Stopwatch
Quantity Mole mol varies
Temperature Kelvin K thermometer
Electric Current Ampere A Ammeter
Luminous Intensity
Candela cd Photometer
NON-SI UNITS
Physical Quantity Unit Name Unit Symbol
Volume Liter L
Pressure Pascal
Atmosphere
Pa
Atm
Temperature Celsius C
Energy Joule J
Derived Units Commonly Used in Chemistry
Physical Quantity How To Calculate: Unit Symbol
Volume Length x Width x Height
Area Length x Width
Density Mass Volume
To Derive a Unit• Write the mathematical formula for the quantity.• Replace the formula with units and simplify.
Density
Density = Mass Volume
a) Calculate the density of a piece of a cube of iron with a mass of 1.23 kg that measures 2 cm on each side.
Temperature
• Measured with: Fahrenheit Scale: An arbitrary scale created by Gabriel Fahrenheit.
F = (C 9/5) + 32
Celsius Scale: Based on the freezing and boiling points of water.
C = (F – 32) 5/9
C = K – 273
Kelvin Scale: The S.I. Scale
•Based on absolute zero.
Absolute Zero: The point at which the motion of particles of matter (their kinetic energy) ceases.
K = C + 273
METRIC CONVERSIONS
METRIC PREFIXES
METRIC PREFIXESPREFIX In 1 base unit there
are:Example
mega- (M) 10-6 M-unit 1 m = 10-6 Mm
kilo- (k) 10-3 k-unit 1 L = 10-3 kL
deka- (dk) 0.1 dk-unit 1 g = 0.1 dkg
BASE UNIT
deci- (d) 10 d-unit 1 s = 10 ds
centi- (c) 100 c-unit 1 mol = 100 cmol
milli- (m) 1000 m-unit 1 m = 1000 mm
micro- () 106 -unit 1 L = 106 L
nano- (n) 109 n-unit 1 g = 109 ng
pico- (p) 1012 p-unit 1 s = 1012 ps
DIMENSIONAL ANALYSIS
What is dimensional analysis?
What is a unit equality?
What is a conversion factor?
What is a conversion factor equal to?
How do you use conversion factors?
Dimensional analysis is a method used to convert between units
A unit equality are two values that are equal to each other (like 3 ft = 1 yd)
A conversion factor is a ratio of a unit equality (3 ft/1yd)
1 (anything divided by an equal value is 1)
Multiply it to a number to convert between units
Steps to Dimensional Analysis1. 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.
DIMENSIONAL ANALYSIS
1 Base Unit Equals
10-6 Mega-10-3 kilo-0.1 deka-10 deci-
100 centi-1000 milli-106 micro-109 nano-1012 pico-