Download Unit 1 Lab Safety Notes

Unit 1
Lab Safety Notes
.
• _________________________ should be worn at all times when
in the lab.
• __________________________ can never be worn in the lab.
All shoes must have ___________________________________________________.
• If your lab partner is on fire, you should _____________________________
_____________________________________________________________.
• If you get chemicals in your eyes (because you are a bad student so you did not wear your
goggles in the lab area), you should use the eye wash station for _______ minutes.
• The _____________________________________ is used to remove noxious fumes and
vapors.
• If you spill a large amount of chemical on you, you should ______________
____________________________________________________________.
• When heating a test tube, you should always ________________________
____________________________________________________________.
• Wafting is a method of smelling chemicals by ________________________
____________________________________________________________.
• You should never ______________ or ________________ in the lab.
• You must complete the __________________________ if you want to participate in the
lab. You MUST read the _________________ before you enter the lab.
Unit 1
Scientific Notation
Scientists often work with very large or very small numbers, which are more easily expressed in
exponential form or scientific notation. You write a very large number in scientific notation by moving
the decimal point to the left until only one digit remains to the left. The number of moves of the
decimal point gives you the exponent. Formally, scientific notation is also known as standard index
notation.
For example:
3,454,000 = 3.454 x 106
For very small numbers, you move the decimal point to the right until only one digit remains to the
left of the decimal point. The number of moves to the right gives you a negative exponent:
For example:
0.0000005234 = 5.234 x 10-7
Practice Problems
0.000 000 000 000 615 g
98 000 000 000 m
0.000 104 s
407 302 000 000 000 Pa
4.38 x 10-7 km
1.89 x 104 L
Addition Example Using Scientific Notation
When adding and subtracting problems written in Scientific Notation the exponents must be the same.
1. The first part of the numbers are added or subtracted and the exponent portion is unchanged.
2. If necessary rewrite the problem in Standard Form for your final answer.
(1.1 x 103) + (2.1 x 103) =
3.2 x 103
Subtraction Example Using Scientific Notation
(5.3 x 10-4) - (2.2 x 10-4) =
3.1 x 10-4
Multiplication Example Using Scientific Notation
You do not have to write numbers to be multiplied and divided so that they have the same
exponents. You can multiply the first numbers in each expression and add the exponents of 10
for multiplication problems.
(2.3 x 105)(5.0 x 10-12) =
When you multiply 2.3 and 5.3 you get 11.5. When you add the exponents you get 10-7. At this point
your answer is:
11.5 x 10-7
You want to express your answer in scientific notation, which has only one digit to the left of the
decimal point, so the answer should be rewritten as:
1.15 x 10-6
Division Example Using Scientific Notation
In division, you subtract the exponents of 10.
(2.1 x 10-2) / (7.0 x 10-3) =
0.3 x 101 =
Unit 1
Percent Error Notes
Accuracy, Precision, and Error
____________ value.
- accuracy can be determined by _______)____ measurement
Accuracy – is how close the measurement is to the
Precision – describes the closeness, or _____________, of a set of measurements taken under the
____________ conditions
- precision is determined by _________________measurements
Accepted (or theoretical) value – a quantity used by general agreement of the scientific community
Experimental (or actual) value – a quantitative value measured during an experiment
Error is the difference between the_ ___________ value and the_ ____________ _ value
Formula
% error = (|Your Result - Accepted Value| / Accepted Value) x 100
| |
Example:
Peter measured the volume of a 2.00 liter bottle of soda. The actual volume of the soda was 1.87
Liters. What is the percent error of the volume of soda?
% error = (|Your Result - Accepted Value| / Accepted Value) x 100
% error = |1.87 L — 2.00 L|
X 100
2.00 L
% error = |- 0.13L| X 100
2.00 L
% error = 0.13L
X 100
2.00 L
% error = 0.065 X 100
% error = 6.5%
Significant Figures
Pacific – Atlantic Rule
•
It's for determining the number of significant figures. Think of the U.S. in a map. The Atlantic
Ocean is to the right. Pacific Ocean to left.
•
If a decimal is present, start counting from the "Pacific" (left).
• If absent, starting count from "Atlantic" (right).
• So, what are we counting? We count the first nonzero digit we encounter; and all subsequent digits
If the decimal is PRESENT, start on the PACIFIC side or _____ __________.
14.020
0.00235
1.04 * 105
If the decimal is ABSENT, start on the ATLANTIC side or _____ t ___________.
7300200
1200
839
Significant Figures are all exact digits of a measurement plus one estimated digit.
Brief determination of the number of significant digits
Rule #1: All non-zero numbers are significant
732 g
Rule #2: Any zero’s between non-zero numbers are significant
301 cm
Rule #3: If there is a decimal point, any zero’s to the right of the last non-zero are significant
a. 320. kg
b. 320 kg
c. 0.70 m
d. 0.070 m
Rule #4: Any number that is used to count things or is a direct conversion has infinite significant figures.
a. 45 desks
b. 60 s = 1 minute
c. 10 pennies = 1 dime
d. 4 beakers
Remember
If the value ___ _____ decimal point, then go to the__ ____ end of the value, moving right, find the first non-zero
number; count it and every number to the right.
⟶0.0012040
If the value does not ____ ______ decimal point, go to the __ ____end of the value, moving to the left find the
first non-zero number; count it and every number to the left.
7201000 ⟵
Significant Figures and Scientific Notation Practice
Underline the significant
figures in the following
measurements and put the
number in scientific
notation:
1. 0.00325 m
Round the following
measurements to the
requested number of
significant figures and
put the number in
scientific notation:
Put the following
measurements in
scientific notation and put
the number in scientific
notation:
1. 0.000000586 m
1. 0.003256 m 2 sig. figs.
2. 12500 s
2. 5620000 g
2. 564025000 g 3 sig. figs.
3. 304.00 g
3. 85000 L
3. 78265 ns 1 sig. fig.
4. 0.00256 kg
4. 0.00236 km
4. 0.236578 Pa 4 sig. figs.
5. 0.0030600 J
25640000000 Pa
5. 0.008596 ng 3 sig. figs.
Perform the following calculations and write the answer with the appropriate number of sig figs AND in
scientific notation.
1. 6.23 x 106 kL + 5.3 x 106 kL
2. 7.525 x 105 kg - 5.43 x 102 kg
3. 4.8 x 105 km x 2.02 x 103 km
4. 8.45 x 102 g ÷ 7.901 x 103 cm3
5. 2.45 x 10-15 J ÷ 3.4 x 10-19 J
6. 20.05 x 10343 – 15.9 x 10341
Rounding off numbers (Using Significant Figures)
Rule #1: If the number after the number to be rounded is less than 5, round down.
Rule #2: If the number after the number to be rounded is greater than or equal to 5, round up.
In a series of calculations, carry extra digits through to the final result and then round off. This
means that you should carry all of the digits that show on your calculator (or most of them) until you
arrive at your final answer and then round off.
Note: Don’t forget significant zeros when writing in scientific notation (ex: 20.0 is 2.00 x 10). Do not
write INsignificant zeros when writing in scientific notation (ex: 6 000 000 is 6 x 106, not 6.000 000 x
106 – this number would have 7 sig figs).
Addition and Subtraction
Rule: Complete the desired calculation and then round off the answer to the number of decimal
places as the value from the problem with the _______ NUMBER OF DIGITS ___ THE DECIMAL.
a)
12.72
34.1
+ 0.463
47.283
47.3
all numbers are significant to
b)
c)
370
+ 101.037
the tenths place.
All numbers are significant to the
______________ place.
900
790.
330
+ 54.8
All numbers are significant to the ______________ place.
Multiplication and Division
Rule: Complete the desired mathematical calculation and then round off the answer to the same
number of significant figures as the value from the problem with the ____________ NUMBER OF
SIGNIFICANT FIGURES.
34.91
x
0.0053 =
0.185023
Rounds to
0.19
four
sig figs
two
sig figs
two
sig figs
Because 0.0053 has only two significant figures, it limits the answer to two significant figures.
3. 102
÷
0.0097 =
Rounds to
Combination of operations
Complete mathematical calculations in correct order and use correct number of significant figures after each step.
Example: (5.2 – 0.2) x 7.00 x 1.00 = 35.00
The difference of 5.2 and 0.2 is 5.0 which is precise to the nearest tenth and has 2 sig. figs. Since 7.00 and 1.00
have 3 sig. figs. The least number of sig figs in the multiplication operation is 2 from the 5.0 difference. The final
answer has 2 sig figs. Answer = 35
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DIMENSIONAL ANALYSIS NOTES:
Metric and English Units Conversions
This page features tables for converting between metric system units and corresponding
English units commonly used in the United States. Here you will find convenient
conversion tables for length, area, volume, weight, pressure, energy and temperature
units. Conversion table calculations show approximately three (3) significant figures.
Length Conversion
Metric length units include the meter, the kilometer (1,000 meters), the decimeter (0.1 meters), the centimeter
(0.01 meters), the millimeter (0.001 meters), the micron (0.000001 meters), the nanometer (0.000000001 or 1e-9
meters), and the angstrom (0.0000000001 or 1e-10 meters).
British and American length units include the foot, the yard (3 feet), the furlong (660 feet), the mile (5,280 feet),
the league (15,840 feet), and the inch (1/12th foot).
Length Conversion Table
Metric Units
English Units
Kilometers
Meters Millimeters
Inches
Feet
Yards
1
1,000
1,000,000
39,370
3,281
1,094
0.001
1
1,000
39.37
3.281
1.094
0.000001
0.001
1
0.03937
0.003281
0.001094
Miles
0.6214
0.0006214
6.214e-7
0.0000254
0.0003048
0.0009144
1.609
0.00001578
0.0001894
0.0005682
1
0.0254
0.3048
0.9144
1,609
25.4
304.8
914.4
1,609,000
1
12
36
63,360
0.08333
1
3
5,280
0.02778
0.3333
1
1,760
Scientists generally work in metric units. Common prefixes used are the following:
Prefix
megakilohectordeka
g/m/l
deci
centimillimicronano-
Abbreviation
M
k
h
da
Meaning
106
103
102
101
Example
1 megameter (Mm) = 1 x 106 m
1 kilogram (kg) = 1 x 103 g
1 hectometer (hm) = 1 x 102 m
1 dekameter (dam) = 1 x 101 m
d
c
m
10-1
10-2
10-3
10-6
10-9
1 decimeter (dm) = 1 x 10-1 m
1 centimeter (cm) = 1 x 10-2 m
1 milligram (mg) = 1 x 10-3 g
1 micrometer ( g) = 1 x 10-6 g
1 nanogram (ng) = 1 x 10-9 g
n
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The Principle behind Dimensional Analysis
The guiding principle of dimensional analysis is that you can multiply anything by “1” without changing
the meaning. An equality set into a fraction formation = 1. For example, if x = y, then x/y = 1 and
y/x=1. Therefore, the equalities can be set into fractions and multiplied to convert units.
Another concept necessary to understanding dimensional analysis is that units that are on the top and
bottom of an expression cancel out.
Example
Let's focus on the first example: Convert 2.50 µg to picograms
STEP ONE: Write the value (and its unit) from the problem, then in order write: 1) a multiplication
sign, 2) a fraction bar, 3) an equals sign, and 4) the unit in the answer. Put a gap between 3 and 4. All
that looks like this:
The fraction bar will have the conversion factor. There will be a number and a unit in the numerator and
the denominator.
STEP TWO: Write the unit from the problem in the denominator of the conversion factor, like this:
STEP THREE: Write the unit expected in the answer in the numerator of the conversion factor.
STEP FOUR: Examine the two prefixes in the conversion factor. In front of the LARGER one, put a
one.
There is a reason for this. I'll get to it in a second.
STEP FIVE: Determine the absolute distance between the two prefixes in the conversion unit. Write it
as a positive exponent in front of the other prefix.
Now, multiply and put into proper scientific notation format. Don't forget to write the new unit.
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Practice Problems
1. 0.75 kg to milligrams
Answer = ___________ mg
2. 1500 millimeters to km
Answer = ___________ km
3. 2390 g to kg
Answer = ___________ kg
10
4. 0.52 km to meters
Answer = ___________ m
5. 65 kg to g
Answer = ___________ g
Website Dimensional Analysis Example:
http://www.khanacademy.org/math/arithmetic/basic-ratios-proportions/v/conversion-between-metricunits?playlist=Developmental%20Math#channel=f275d6f01f13244&origin=http%3A%2F%2Fwww.khanacademy
.org&channel_path=%2Fmath%2Farithmetic%2Fbasic-ratios-proportions%2Fv%2Fconversion-between-metricunits%3Fplaylist%3DDevelopmental%2520Math%26fb_xd_fragment%23xd_sig%3Df398c9ff7e273ce%26
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Practice SI Unit Conversions (Single Unit Conversion)
1. Convert 0.0036 g to mg
1000 mg
0.0036 g x 1g
2. Convert 8.9 x 10-8 s to min
= 3.600 g (remember sig figs!)
3. Convert 8200000nPa to MPa
4. Convert 3.26 L to cm3
5. Convert 0.0012 cm3 to mL
6. Convert 6500 dm3 to cm3
7. Convert 0.29 L to cm3
8. Convert 2.96 x 1014 nL to kL
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SI Unit Conversions Practice
Multiple Unit Conversion
Example
Sample 1: If light from the sun takes 8.11 minutes to get to the Earth, how far away is the sun in km?
(speed of light is 3.0x108m/s and there are 1000 m in one km).
1. Identify the values in the problem, include units.
8.11 minutes
km away from the earth
Speed of light is 3.0x108m/s
2. Start with the value with only one unit.
8.11 minutes
3. Put that starting unit into the denominator to cancel units out.
8.11 minutes X 60 seconds
1
1 minute
=
4. Find the value OR conversion to a given value with the same unit and place it into the problem.
8.11 minutes X 60 seconds
1
1 minute
= 486.6 seconds
5. Repeat until you get to the desired units, cross out units which cancel.
3.0 x108 m
1 seconds
486.6 seconds X
1
=
14.598 x1010 m = 1.4598 x1011 m
6. Solve and put into correct scientific notation (multiply numerator and divide denominator).
1.4598 x1011 m
1
X
1 km
1000 m
=
1.4598 x108 km
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DIMENSIONAL ANALYSIS PRACTICE PROBLEM:
If you live 3.2 miles from your best friend and the speed limit is 25 miles/hour, how many seconds will it
take you to drive from your house to your friend’s house?
You want to earn $600 to buy a new bicycle. You have a job that pays $6.75/hour, but you can work
only 3 hours/ day. How many days before you will have enough to buy the bike?
Someone that never learned dimensional analysis went off to work at a fast food restaurant for the past
35 years wrapping hamburgers. Each hour you wrap 184 hamburgers. You work 8 hours per day. You
work 5 days a week. You get paid every 2 weeks with a salary of $840.34. How many hamburgers will
you have to wrap to make your first one million dollars?
In 1973 the Emergency Highway Energy Conservation Act instituted a National Maximum Speed Law
of 55 mph. How many minutes would it take to travel 16 kilometers? (1 mile = 1.6093 km)?
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