Embed Size (px)
Citation preview
Chapter 2-1Chapter 2-1Method, Method,
MeasurementMeasurementand Problem and Problem
SolvingSolving
I. What is Chemistry?
A. Chemistry is the study of all matter and the changes it can undergo.
B. Chemistry has been called the central science because it overlaps so many sciences.
C. Chemical – any substance with a definite composition.
Ex) dihydrogen monoxide = H2O
A common misperception of science is that science defines "truth." Science does not define truth, but rather it defines a way of thought. It is a process by which experiments are used to answer questions. This process is called the scientific method and involves several steps:
II. The Scientific Method: (2.2)
A. A systematic approach to gathering knowledge.
B. Steps to the Scientific Method:1. observation2. question3. hypothesis4. experiment5. conclusion
*Note: All hypotheses must be able to be
tested in order to be a true hypothesis.
C. Many Experiments Natural Law Theory
(how nature behaves) (why nature behaves)
III. Scientific Notation: Shorthand way of expressing very large or very small numbers. (2.3)Power of 10 Equivalent # Reason
100 1 Any # to the zero power is 1
101 10 10 x 1
102 100 10 x 10
103 1,000 10 x 10 x 10
105 100,000 10 x 10 x 10 x 10 x 10
10-1 0.1 1/10
10-3 0.001 1/(10x10x10) = 1/1000
10-5 0.00001 1/(10x10x10x10x10) = 1/100,000
•B. Express Numbers in Scientific Notation – move the decimal point so that there is only 1 non-zero digit to the left of the decimal point. Moving the decimal point left the power will be -, right the power will be +.
Try these examples: top of page 2 in the notes!
1) 2700 2) 0.0035
3) 2,640,000,000 4) 0.010
C. Express Numbers in regular form – reverse the process.
5) 8.65 x 106 6) 9.73 x 10-8
Complete the front of the Scientific Notation Worksheet
2.7 x 103
3.5 x 10-
3
2.64 x 109 1.0 x 10-
2
8,650,000 0.000 000 0973
1x100 = 1
1x10-10
1x10-1
Large Numbers
0
1x102
NegativeNumbers
4x101
Small Numbers – negative exponents are all between 0 and 1
Find the “EE” key – it may be a 2nd function!
Find the (-) key.If you have a graphing calculator look for the following keys:
1st Commandment of Chemistry: KNOW THY CALCULATOR!
Find the “Exp” or “x10x”
Find the “(-)” or the “+/-” key.
Look at the calculator
that is similar to yours…
1st Law of Chemistry:
Know Thy Calculator!
Try these examples:Ex. #7) 8.08 x 10-5 - 2.07
x 10-6 =
Ex. #8) 3.7 x 102 x 5.1 x 103 =
Ex. #9)
-3
-7
2.3 x 10
4.6 x 10
7.87 x 10-5
1,887,000 or 1.887 x
106
5000 or 5 x 103
Origin of the Metric System
During the18th century scientists measured the distance from the earth’s equator to the North Pole and divided it into ten million parts.
This number is equal to exactly 1 meter.
The Meter
The standard for the meter is kept in a safe in France.
The meter stick is a replica of that standard.
A meter is made up of 100 centimeters and 1000 millimeters.
Demo Volunteers!
The Liter
The liter is 1000 mL 10cm x 10cm x 10cm 1 liter = 1000 cm3 = 1 dm3
1 milliliter = 1 cm3 = 1 cc = 20 drops
=
The Gram
Mass is the amount of matter in an object.
1 cm3 of water = 1 gram.
The standard kilogram is kept under lock and key at the Bureau of International Weights and Measures in Sevres, France.
The Time standard
During the 15th century a scientist named Galileo set the standard of time known as the second.
Why do we need standards????
Mars Climate Orbiter Mistake
In December 1998 two different groups of scientists were working on calculations to land a probe on Mars.
The American team did their calculations in the English system and the other team did their calculations in the metric system – the $125 million probe crashed onto Mars in September 1999.
In 2004, doctors prescribed 0.75 mL of Zantac Syrup twice a day to a baby, but the pharmacist labeled the bottle, “Give 3/4 teaspoonful twice a day.”
A teaspoon is about 4.9 mL… The mistake was 5 times the correct dose!
Medication Dose Errors
Length Relationships
IV. Metric System: (1.2)
A. International System of Measurements (SI): standard system used by all scientists. It is based upon multiples of 10.
Measurement Unit Instrument Equation Derived Unit
Mass gram triple beam balance ------------ ---------------
length Meter meterstick ------------ ---------------
time second watch ------------ ---------------
TemperatureKelvin/
celciusthermometer ------------ ---------------
Quantity mole ----------------------- ------------ ---------------
Area m2/cm2 meterstick L x W cm2
Volume m3/cm3 Graduated cylinder LxWxH L
Density g/cm3 ---------------------- D = M/V g/cm3
Pressure Atm/kPa barometer Force/area N/m2
Energy Cal or J Calorimeter ---------------- Cal/Joules
Prefix Abbreviation Meaning Scientific Notation
Giga G 1,000,000,000 1 x 109
Mega- M 1,000,000 1 x 106
kilo- k 1,000 1 x 103
hecto- h 100 1 x 102
deka- da or dk 10 1 x 10
BASE UNIT meter/liter/gram 1 1
deci- d 0.1 1 x 10-1
centi- c 0.01 1 x 10-2
milli- m 0.001 1 x 10-3
micro- µ 0.000 001 1 x 10-6
nano-n 0.000 000 001 1 x 10-9
pico- p 0.000 000 000 001 1 x 10-12
D. Metric Conversions using the
Factor-Label Method (Dimensional Analysis)Ex. #1) Convert $72 to quarters:
Write the given with the units. Then look at the unit and use a conversion factor that relates to the unit you need.
See page 3 in the notes
72 dollars4 quarters
1 dollar
V. Uncertainty in Measurement: (2.3)
A. Measurements are uncertain because:1. Instruments are not free from
error.2. Measuring always involves some
estimation.B. Estimating with a scale
1. Estimate 1 digit more than the
instrument measures.
2. “” is used to show uncertainty.
READ the length of the lines:
Smallest graduations on the ruler are 0.1cm therefore you should measure to 0.01cm!
2.83cm .01cm
2.00cm .01cm
C. Precision: When the instrument gives you about the same results under similar conditions.
D. Accuracy: When the experimental value is close to the true or actual value. The smaller the increments of measurement an instrument has, the more accurate it can be.
E. An instrument is precise (numbers repeatable to a certain number of places) the operator makes it accurate (close to the right answer by using it correctly).
Ex. Precise, Accurate, Both or Neither (Accepted Value = 15g)
1. 200g, 1g, 40g neither2. 78g, 80.g, 79g precise3. 16g, 14g, 17g both precise and
accurate
What is the goal for a game of darts?
Hitting the Bulls Eye!
Reading a Metric Ruler
Meter sticks and paperclips!
3 4 5
3 4 5
Rulers
3 4 5
3.6 cm
3.6 cm
3.62 cm
How to use a graduated cylinder
Read the meniscus
How to use a graduated cylinder
36.4 mL 19.0 mL 6.25 mL
More Graduated Cylinders
15.2 mL 8.69 mL 17 mL
Because the smallest increments on the
graduated cylinder are 0.1 mL, you estimate
the .01 place…The cylinder reads 8.76
mL
130.510 g
Triple Beam Balance
0 100 200
0 10 20 30 40 50 60 70 80 90 100
0 1 2 3 4 5 6 7 8 9 10
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
Reading a Triple Beam Balance
146.440 g
How to read a Triple Beam Balance
Ohaus Triple Beam Balance Tutorial
Reading A Triple Beam Balance Tutorial
28.570 g
How to read a Triple Beam Balance
Ohaus Triple Beam Balance Tutorial
Reading A Triple Beam Balance Tutorial
109.076 g
D. Factors in an Experiment
1. Independent: most regular variable – goes on the X-axis2. Dependent: what you are testing – goes on the Y-axis3. Experimental Control: part of the experiment that stays
the same.
Independent variable
“X” axis
Dependent variable
“Y” axis
Drawing a Graph in Chemistry:
• Label each axis with a name and a unit.
• Number by regular increments! This means by 1’s, 2’s, 5’s, 10’s etc. NOT by 3’s,7’s or 9’s!
• Unless otherwise noted include zero.
• Include a title that states what is being tested…this would include the dependent variable and any change that occurs for different trials.
• Include a key for different trials. This could be different colors or one in pen and one in pencil.
• Write a statement or conclusion on the graph that states; “This graph shows…” to explain the results of the experiment.
• If necessary, extend the graph (extrapolate) to predict additional data points with a dashed (-----) line.
Title: How pressure changes with increased volume.
Key:
Trial 1
Trial 2
Statement: This graph shows that pressure decreases with increased volume.
Graphing: How do you determine the best-fit line through data points? The line may pass through some, all or none of the data points.
x-variable
y-variable
Are the data directly or indirectly related, is the general trend 1st degree (straight line) or 2nd degree (curved)?
Rules for Significant Digits!
All nonzero digits are significant. All zeros between two nonzero digits are
significant. All zeros to the left of an understood decimal
point, but to the right of a nonzero digit are not significant.
All zeros to the left of an expressed decimal point, and to the right of a nonzero digit are significant.
All zeros to the right of a decimal point, but to the left of a nonzero digit are not significant.
All zeros to the right of a decimal point and to the right of a nonzero digit are significant.
Can you think of a map of the United
States?
Then you can do significant digits!
VI. Significant Digits
A. Significant Digits include measured digits and
estimated digits. Use Atlantic-Pacific Rule – imagine a
US map
Atlantic
Pacific
decimal
point
decimal
point
1100
1100.
11.010000 0.025
0.00035000
2 significant digits4 significant digits8 significant digits2 significant digits5 significant digits
Decimal Absent Start counting with the 1st nonzero digit and count all the rest.
Decimal Present Start counting with the 1st nonzero digit and count all the rest.
1,000,100 5 significant digits
B. Significant Digits in Addition and Subtraction
1. Add or Subtract numbers.2. Answer must be based on the number
with the largest uncertainty (look at least places.)
Ex. 951.0 g1407 g 23.911g 158.18 g +
2540.091g ?
Which is the least precise place??? Round your answer to that place:
ones placethousandths placehundredths place
tenths place
2540.g
B. Multiplication and Division1. Multiply or Divide numbers.2. Round answer to the same number of
significant digits as number with fewest significant digits.
Ex #1) =
Ex #2) V = L x W x H V= 3.05 m x 2.10 m x 0.75 m =
7.079 cm
0.535 cm
4
3
13.2 no units!
4.8 m33 23
Ex. #3) A = L x W A= 3200 cm x 2500 cm = ? Always write down the answer your
calculator gives you, then round to the correct # of S.D.
= 8,000,000 cm2
This only has 1 S.D. How many S.D. should the answer have? If you can’t round, write the number in
scientific notation: = 8.0 x 106 cm2
2
VII. Important Formulas:A. Percent Error: Comparing a
measurement obtained experimentally with an accepted value. It is always expressed as a positive %.
% error =
Ex.) If a student calculates the density of aluminum to be 2.5 g/cm3, and the accepted value is 2.7g/cm3, what was her % error?
measured value - accepted value x 100% =
accepted value
3 3
3
3
3
2.5 g/cm - 2.7 g/cm x 100%
2.7 g/cm
.2 g/cm x 100% = 7.4 = 7%
2.7 g/cm
Ex.) If a student calculates the density of aluminum to be 2.5 g/cm3, and the accepted value is 2.7g/cm3, what was her % error?
measured value - accepted value% error = x 100%
accepted value
Density is defined as mass per unit volume. It is a measure of how tightly packed and how heavy the molecules are in an object. Density is the amount of matter within a certain volume.
Which is less dense???
Units for density g/cm3 or g/ml
Formula: M = mass V= volume D = density
M = D x V V = M / D D = M / V
1) Find the mass of the object with the triple beam balance…you may have to subtract the mass of the container!
2) Find the volume of the object – use a graduated cylinder for liquids and a centimeter ruler for regular solids.
3) Divide : Density =
To find density:
What if it’s an irregular shaped solid and not a liquid???
Mass
Volume
Density of an Irregular solid:
1- Find the mass of the object2- Find the volume of the object by water
displacement!
B. (1.2) Density M=VD
V=
• Ex.) If a metal block has a mass of 75.355 g and a
volume of 22.0 cm3, what is the density? D =
M
D
Mass
Volume
33
75.355 gD = = 3.43 g/cm
22.0 cm
Would the above metal block float or sink in water???
What is the density of water?
1.0 g/mL
VIII. Dimensional Analysis (The Factor-Label Method): (1.2)A. Uses unit equalities to convert between
units. A unit equality is an equation that relates 2 units.
Ex.) 12in = 1ft 60sec = 1min 1kg = 1000g
B. Unit equalities are used to write conversion factors which are always equal to “1.”
Ex)
1000 m = 1
1 km
1 km or = 1
1000 m
C. The conversion factor is a definition, and therefore infinitely precise, so the number of significant digits in the answer is equal to the number in the given.
Useful Chemistry Conversion Factors
1 in. = 2.54 cm
1 ft. = 12 in.
1 mile = 5280 ft.
1 min. = 60 s
1 hr. = 60 min.
1 atm = 760 mm Hg
1 atm = 101,325 Pa
1 cal. = 4.184 J
1 gal. = 3.785 L
These conversion factors will
NOT be given on the test. In addition you need to know
the 6 basic metric
prefixes.
Ex. #1) How many seconds are in 22.0 hours?
60 min 60s22.0 hr 79,200s
1 hr 1min
8 1 min 1 hr 1 day 1 year3 x 10 sec 10 years
60 sec 60 min 24 hours 365 days
Ex. #2) How many years are in 3 x 108
seconds?
Ex. #3) If there are 9 dibs in 1 sob, 3 sobs in 1 tog, 1 tog in 6 pons, and 12 pons in 1 gob. How many gobs are in 27 dibs? 1 sob 1 tog 6 pons 1 gob
27 dibs 0.50 gobs 9 dibs 3 sobs 1 tog 12 pons
Ex #4) Calculate the number of feet in a 5.00 km race. (1 inch = 2.54 cm)
1000 m 100 cm 1 inch 1 ft5.00 km 16,400 ft
1 km 1 m 2.54 cm 12 in
