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Ma#er, Measurements, and Calcula1ons
Agenda
• REVIEW scien1fic nota1on, rounding and significant digits-‐ P. 649-‐654
• Unit conversions – handouts\ worksheets • HW: complete scien1fic nota1on, rounding, sig. digits and metric conversions worksheets
Chemistry – the study of MATTER
Chemistry: The branch of science that deals with the iden1fica1on of the substances of which ma#er is composed; the inves1ga1on of their proper1es and the ways in which they interact, combine, and change; and the use of these processes to form new substances.
(Ma#er = anything that has mass and takes up space)
Physical Proper1es of Ma#er
Intensive -‐ Proper1es that do not depend on the amount of the ma#er present.
Ex: Color, Odor, Luster, Malleability, Duc1lity, Conduc1vity, Hardness, Mel1ng/Freezing Point, Boiling Point, Density
Extensive -‐ Proper1es that do depend on the amount of ma#er present.
Ex: Mass, Volume, Weight, Length
Physical properties of matter are categorized as either Intensive or Extensive:
The Metric System
from
Indu
stry
Wee
k, 1
981
Nov
embe
r 30
Scien1fic Method
• The process researchers use to carry out their inves1ga1ons. It is a logical approach to solving problems.
Steps 1. Ask a ques1on 2. Observe and collect data 3. Formulate a hypothesis (a testable if-‐then
statement). The hypothesis serves as a basis for making predic1ons and for carrying out further experiments.
4. Test your hypothesis – Requires experimenta1on that provides data to support or refute your hypothesis.
Terms to Know Law vs. theory
• Scien2fic (natural) Law: a general statement based on the observed behavior of ma#er to which no excep1ons are known.
• Empirical Data-‐ collected by experimenta1on and detected by 5 senses.
Quan2ty: number + unit Qualita2ve: descrip1ve (color, shape)
Theory: a broad generaliza1on that explains a body of facts or phenomena. ( explana1ons, models, symbols, analogies, etc.)
SI (System of Interna1onal) Units of Measurements
• Adopted in 1960 by the General Conference on Weights and Measures.
Metric System – must know this
• Mass is measured in kilograms (other mass units: grams, milligrams)
• Volume in liters • Length in meters
Prefixes are added to the stem or base unit to represent quan11es that are larger or smaller then the stem or base unit. You must know the
following:
Prefix Value Abbrevia2on Ex Pico 10-‐12 0.000000000001 p pg Nano 10-‐9 0.000000001 n nm Micro 10-‐6 0.000001 µ µg Milli 10-‐3 0.001 m mm Cen1 10-‐2 0.01 c cl Deci 10-‐1 0.1 d dg (stem: liter, meter, gram) Deca 101 10 da dal Hecto 102 100 h hm Kilo 103 1000 k kg Mega 106 1000000 M Mm
Quan11es of Mass
Kelter, Carr, Scott, Chemistry A Wolrd of Choices 1999, page 25
Earth’s atmosphere to 2500 km
Ocean liner
Indian elephant
Average human 1.0 liter of water
Grain of table salt
Typical protein
Uranium atom Water molecule
1024 g 1021 g
1018 g
1015 g
1012 g
109 g
106 g
103 g
100 g
10-3 g
10-6 g
10-9 g
10-12 g
10-15 g
10-18 g
10-21 g 10-24 g
Giga- Mega-
Kilo-
base
milli-
micro-
nano-
pico-
femto-
atto-
http://htwins.net/scale2/scale2.swf
Star1ng from the largest value, mega, to the smallest value, pico, a way to remember the
correct order is: • Miss (Mega)
• Kathy (Kilo) • Hall (Hecto) • Drank (Deca) • Gatorade, Milk, and Lemonade (Gram, Meter, Liter) • During (Deci) • Class on (Cen1) • Monday (Milli) • Morning and (Micro) • Never (Nano) • Peed (Pico)
Factor Name Symbol Factor Name Symbol
10-1 decimeter dm 101 decameter dam
10-2 centimeter cm 102 hectometer hm
10-3 millimeter mm 103 kilometer km
10-6 micrometer µm 106 megameter Mm
10-9 nanometer nm 109 gigameter Gm
10-12 picometer pm 1012 terameter Tm
10-15 femtometer fm 1015 petameter Pm
10-18 attometer am 1018 exameter Em
10-21 zeptometer zm 1021 zettameter Zm
10-24 yoctometer ym 1024 yottameter Ym
Convert the following: a) 1600.0 m = ____________ km
1600.0/ 10 3 =
1600.0 x 10 -‐3 =1.6000 km = 1.6000 x 10 0 km
b) 0.050 km = ___________ m 0.050 x 10 3 = 50 m= 5.0 x 10 2 m
Convert the following: c) 10.24 kg = ______________ mg
10.24 x 10 6 =10240000 mg = 1.024 x 10 7 mg
d) 0.076 µm = ____________ dam
0.076/ 10 7 = 0.076 x 10 -‐7 = 0.0000000076 dam =
7.6 x 10 -‐9 dam
Temperature-‐ Be able to convert between degrees Celsius and Kelvin.
Absolute zero is 0 K, a temperature where all molecular mo1on ceases to exist. Has not yet been a#ained, but scien1sts are within thousandths of a degree of 0 K. No degree sign is used for Kelvin temperatures. Celsius to Kelvin: K = °C + 273 Convert 98 ° C to Kelvin: 98° C + 273 = 371 K
Example
New materials can act as superconductors at temperatures above 250 K. Convert 250 K to degrees
Celsius.
ANS: -‐ 230C
250 K -‐ 273 = -‐ 23 °C
Derived Units
Derived Units: combina1ons of quan11es: area (m2), Density (g/cm3), Volume (cm3 or mL) 1cm3 = 1mL
Density – rela1onship of mass to volume D = m/V Density is a derived unit (from both
mass and volume)
• For solids: D = grams/cm3 • Liquids: D = grams/mL • Gases: D = grams/liter
• Know these units
Density is a conversion factor. Water has a density of 1g/mL which means 1g =1mL!!
Density
Which box is more dense? Both cubes have the same volume, but Cube 1 has more
molecules so it is denser than the Cube 2!
Density of Liquids
Liquids of lower density float on liquids of higher density.
Vegetable Oil
Density= .95 g/mL
Water
Density= 1.0 g/mL
The Factor-‐ Label Method-‐ P.652 Dimensional analysis involves using conversion factors to cancel units un1l you have the proper unit in the proper place. A conversion factor is a ra1o of equivalent measurements, where one measurement is equal to one.
Example conversion factors: 4 quarters = $1.00 à 4 quarters / $1.00 1 kg = 1000 g à 1kg / 1000 g 1 kg = 2.2 lbs à 1 kg / 2.2 lbs
Density as a Conversion Factor Density is a conversion factor that relates mass and volume. Example Problem: The density of mercury is 13.6 g/mL. What would be the mass of 0.75 mL of mercury?
ANS: 10.2 g
CHALLENGE EXAMPLE: How many atoms of copper are present in a pure copper penny? The mass of the penny is 3.2 grams. Needed conversion factors: 6.02x1023 atoms = 1 mole copper 1 mole copper = 63.5 grams
PROBLEM SOLVING STEPS
3. Mul1ply all the values in the numerator and divide by all those in the denominator.
4. Double check that your units cancel properly. If they do, your numerical answer is probably correct. If they don’t, your answer is certainly wrong.
Agenda
• MORE PRACTICE ON SIGNIFICANT DIGITS • HW: complete scien1fic nota1on, rounding, sig. digits worksheets
How big?
Measurements and Significant Digits
How small?
How accurate?
Using Scien1fic Measurements
Precision and Accuracy 1. Precision – the closeness of a set of measurements of the same quan11es made in the same way (how well repeated measurements of a value agree with one another).
2. Accuracy – is determined by the agreement between the measured quan1ty and the correct value.
Ex: Throwing Darts ACCURATE = CORRECT
PRECISE = CONSISTENT
Accuracy vs. Precision
Random errors: reduce precision
Good accuracy Good precision
Poor accuracy Good precision
Poor accuracy Poor precision
Systematic errors: reduce accuracy
(person) (instrument)
Precision Accuracy
v reproducibility v check by repeating measurements
v poor precision results from poor technique
v correctness v check by using a different method
v poor accuracy results from procedural or equipment flaws.
Percent Error
is calculated by subtrac1ng the experimental value from the accepted value, then dividing the difference by the accepted value. Mul1ply this number by 100. Accuracy can be compared quan1ta1vely with the accepted value using percent error.
Measurement • Exact number
-‐ results from coun1ng items that cannot be subdivided
-‐ has an infinite number of significant digits. • Approximate number -‐ results from measuring -‐ does not express absolute accuracy -‐ has a defined number of significant digits that
depends on the accuracy of the measuring device
Repor1ng Measurements
• Using significant figures
• Report what is known with certainty
• Add ONE digit of uncertainty (es1ma1on)
Coun1ng Significant Figures
• When you report a measured value it is assumed that all the numbers are certain except for the last one, where there is an uncertainty of ±1.
• Example of nail: the nail is 6.36cm long. The 6.3 are certain values and the final 6 is uncertain! There are 3 significant figures in the value 6.36cm (2 certain and 1 uncertain). All measured values will have one (and one only) uncertain number (the last one) and all others will be certain. The reader can see that the 6.3 are certain values because they appear on the ruler, but the reader has to es1mate the final 6.
Significant Figures
• Indicate precision of a measurement.
• Recording Significant Figures (SF) – Sig figs in a measurement include the known digits plus a final es1mated digit
2.35 cm
Prac1ce Measuring
4.5 cm
4.54 cm
3.0 cm cm 0 1 2 3 4 5
cm 0 1 2 3 4 5
cm 0 1 2 3 4 5
20
10
15 mL ?
15.0 mL?
1.50 x 101 mL
The rules for coun1ng the number of significant figures in a value are:
1. All numbers other then zero will always be counted as significant figures.
2. Cap1ve zeros always count. All zeros between two non-‐zero numbers are significant.
3. Leading zeros do not count. Zeros before a non-‐zero number awer a decimal point are not significant.
4. Trailing zeros count only if there is a decimal. -‐ All zeros awer a non-‐zero number, awer a decimal point are significant.
-‐ Zeros awer a non zero number with no decimal point are not significant.
There are rules that dictate the number of significant digits in a value. 1. Read the Significant Digits handout up to A. 2. Try A
Answers to question A 1. 2.83 2. 36.77 3. 14.0 4. 0.0033 5. 0.02 6. 0.2410 7. 2.350 x 10 – 2 8. 1.00009 9. 3 10. 0.0056040
3 4 3 2 1 4 4 6
infinite 5
Rounding Rounding using the sta1s1cal approach: When a number ends in 5 and only 5 when you need to round: • If the preceding number is even –leave it, don’t round up Ex. The number 21.45 rounded off to 3 significant figures becomes • If the preceding number is odd – round up Ex. The number 21.350 rounded off to 3 significant figures becomes BUT If any nonzero digits follow the 5, raise the preceding digit by 1. Ex. The number 21.4501 rounded off to 3 significant figures becomes
21.4
21.4
21.5
Scien1fic notation • All significant digits must be maintained • Only one number is wri#en before the decimal point and express the decimal points as a power of ten.
9.07 x 10 –
2 m 0.0907m
5.06 x 10 –
4 cg 0.000506cg
2.3 x 1012 m 2 300 000 000 000m
1.27 x 102 g 127g Scientific notation Decimal notation
Scien1fic notation • If your value is expressed in proper scien1fic
nota1on, all of the figures in the pre-‐exponen1al value are significant, with the last digit being the least significant figure. “7.143 x 10-‐3 grams” contains 4 significant figures
• If that value is expressed as 0.007143, it s1ll has 4 significant figures. Zeros, in this case, are placeholders. If you are ever in doubt about the number of significant figures in a value, write it in scien1fic nota1on.
Give the number of significant figures in the following values:
a. 6.19 x 101 years b. 7 400 000 years c. 3.80 x 10-‐19 J • Helpful Hint :Convert to scien1fic nota1on if you
are not certain as to the proper number of significant figures.
• When solving mul1ple step problems DO NOT ROUND OFF THE ANSWER UNTIL THE VERY END OF THE PROBLEM.
ANS: a. 3 b. 2 c. 3
Significant Digits • It is be#er to represent 100 as 1.00 x 102 • Alterna1vely you can underline the posi1on of the last significant digit. E.g. 100.
• This is especially useful when doing a long calcula1on or for recording experimental results
• Don’t round your answer un1l the last step in a calcula1on.
• Note that a line overtop of a number indicates that it repeats indefinitely. E.g. 9.6 = 9.6666…
• Similarly, 6.54 = 6.545454…
Fill in the table Ordinary Nota2on ( g) Scien2fic Nota2on (g) # of Significant Figures
0.0012 0.00102 0.00120 1.200 12.00 1200 1200
1.2 x 10 -‐3 2 1.02 x 10 -‐3
1.20 x 10 -‐3
1.200 x 10 0
1.200 x 10 1
1.2 x 10 3
3 3 4 4 2
3 1.20 x 10 3
Significant Figures in Calcula1ons 1. In addi2on and subtrac2on, your answer should have
the same number of decimal places as the measurement with the least number of decimal places.
Example: 12.734mL -‐ 3.0mL = __________
Solu1on: 12.734mL has 3 figures past the decimal point. 3.0mL has only 1 figure past the decimal point. Therefore your final answer should be rounded off to one figure past the decimal point. 12.734mL -‐ 3.0mL
9.734 -‐-‐-‐-‐-‐-‐-‐-‐à 9.7mL
Adding with Significant Digits
• E.g. a) 13.64 + 0.075 + 67 b) 267.8 – 9.36
13.64 0.075
67. 80.715 81
267.8 9.36
258.44 • Try ques1on B on the handout
– + +
B) Answers
83.14
i) 83.25 0.1075 –
4.02
4.02 0.001 +
ii)
1.82
0.2983 1.52 +
iii)
Mul1plying with Significant Digits 2. In mul2plica2on and division, your answer should have
the same number of significant figures as the least precise measurement (or the measurement with the fewest number of SF).
Examples: a. 61cm x 0.00745cm = 0.45445 = = 2SF 3SF 2SF
b. 608.3m x 3.45m = 2098.635 = 4SF 3SF 3SF
c. 4.8 g ÷ 392g = 0.012245 = 2SF 3SF 2SF
• Try ques1on C and D on the handout (recall: for long ques1ons, don’t round un1l the end)
0.45cm2
2.10 x 103 m2
0.012 or 1.2 x 10 – 2
4.5 x 10-‐1 cm2
C), D) Answers i) 7.255 ÷ 81.334 = 0.08920 ii) 1.142 x 0.002 = 0.002 iii) 31.22 x 9.8 = 3.1 x 102 (or 310 or 305.956) i) 6.12 x 3.734 + 16.1 ÷ 2.3
22.85208 + 7.0 = 29.9 ii) 0.0030 + 0.02 = 0.02
135700 =1.36 x105
1700 134000 +
iii) iv) 33.4
112.7 + 0.032 +
146.132 ÷ 6.487 = 22.5268 = 22.53
Note: 146.1 ÷ 6.487 = 22.522 = 22.52
Calcula1ons & Significant Digits In mul1ple step problems if addi1on or subtrac1on AND mul1plica1on or division is used the rules for rounding are based off of mul1plica1on and division (it “trumps” the addi1on and subtrac1on rules). There is no uncertainty in a conversion factor; therefore they do not affect the degree of certainty of your answer. The answer should have the same number of SF as the ini2al value.
a. Convert 25 meters to millimeters. b. Convert 0.12L to mL.
?mm→ 25 m X 1000 mm = 25 000 mm 1 1 m 2SF
?mL→ 0.12L X 1000 m = 120 mL 1 1 L 2SF
Unit conversions & Significant Digits • Some1mes it is more convenient to express a value in different units.
• When units change, basically the number of significant digits does not.
E.g. 1.23 m = 123 cm = 1230 mm = 0.00123 km • No1ce that these all have 3 significant digits • This should make sense mathema1cally since you are mul1plying or dividing by a term that has an infinite number of significant digits.
conversion factors= infinite # of sig. digits E.g. 123 cm x 10 mm / cm = 1230 mm • Try ques1on E on the handout
E) Answers
• A shocking number of pa1ents die every year in United States hospitals as the result of medica1on errors, and many more are harmed. One widely cited es1mate (Ins1tute of Medicine, 2000) places the toll at 44,000 to 98,000 deaths, making death by medica1on "misadventure" greater than all highway accidents, breast cancer, or AIDS. If this es1mate is in the ballpark, then nurses (and pa1ents) beware: Medica1on errors are the forth to sixth leading cause of death in America.
i) 1.0 cm = 0.010 m
ii) 0.0390 kg = 39.0 g
iii) 1.7 m = 1700 mm or 1.7 x 103 mm
RACE FOR KNOWLEDGE
In your groups, designate one person as the” runner”. You are to work through the sheet in order. You may not answer any other ques1ons un1l the previous one had been approved. Work together to come to an agreement on the correct answer.
RACE FOR KNOWLEDGE
1. Write correct answer to ques1on # 1 in the column to the right. 2. Have the “ runner fast walk( no running) the paper up to the teacher for confirma1on. 3. If correct, bring your paper back to your group and determine the answer to # 2. 4. If incorrect, you must go back to your group, correct the answer and bring it up again for confirma1on before moving on. 5. The first group to correct complete sheet wins.