Measurement and Significant Figures
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Transcript of Measurement and Significant Figures
How to survive and thrive AP ChemIsTRY
Steps to survive & thrive in AP Chem!1 Review all of your old notes from chemistry class. If
you don't have those, ask somebody who has taken neat notes from a prior class and study those. The main point here is to simply refresh your memory: you're not going to remember it all or even be close.
2 Walk into AP Chemistry with some confidence and swagger. Don't be intimidated: do it to it.
3 Take notes and make flashcards of ideas and formulas. Try to synthesize your own flashcards and not just copy from the book and your notes.
4 Read the chapter at least three times before the test. Sounds like overkill, but it's not.» "How should you study? Study like there's going to be
an exam on the material the next morning. If you study like that, you won't have to worry about cramming for the exam later." - Unknown professor.
5 Keep in mind your fundamental properties of everything chemistry related. Start with the basic states of matter and end with the chemical properties such as pH and electronegativity. Cover the bases.
6 Don't be afraid of pH. It's a pain in the butt, yes. Will it hurt you to do outside practice problems from the internet? Of course not.
7 Use the internet often for extra practice. There are countless resources out there on the internet, and the problems are all different. Meaning: you won't get a narrow mental work out.
8 Watch your stoichiometry. A lot of problems will be set up perfectly within the problem itself, keep your eyes peeled.
9 Memorize your strong acids and bases. They ionize 100%, and are therefore pretty darn important.
10 It's okay if you don't get it right the first time.
How to survive and thrive AP ChemIsTRY
11 Try again and again. Until you get it perfect.12 Work through old tests and practice
tests on the internet. It could be the difference between passing and failing the exam.
13 Make mnemonic devices for everything. It especially helps with cations and anions.
14 Do ALL of your homework assignments. Some teachers look simply for effort.
15 Practice makes perfect test scores. By doing problems related to your current material, you can be fully readied for that material's test or quiz.
How to survive and thrive AP ChemIsTRY
UNIT 0 REVIEW• Purchase 5 steps to a 5
• 2013-2014 edition (NOT OLD)• Review• VERY FAST – look at your notes, find
where you were weak and START STUDYING
• Review thru pg 11 in class, rest on your own• Help as needed• Use old notes• Use links on website!! Lots of help
online!
Scientific problem solving1. Observations
- quantitative (involve #’s or measurement)
- qualitative ( don’t invole #’s)
2. Formulating hypothesis- possible explanation for
the observation3. Performing experiments
- gathering new information to decide whether the hypothesis is valid
- Results and observations lead to modifying the hypothesis
Theories become laws
Eventually, after many experiments the hypothesis may graduate to become a theoryo A theory gives a universally accepted
explanation of the problemA theory gives a universally accepted
explanation of the problem.Theories should be constantly challenged
and refined with new data and evidence.
Theories become laws
Theories are different from laws.Laws state the general behavior
that occurs naturally in nature.Ex: Law of conservation of Mass
is a law because we have observed over and over that mass is not created or destroyed but only changes form.
Law vs. TheoryA law summarizes what happens
A theory (model) is an attempt to explain why it happens.
Einstein's theory of gravity describes gravitational forces in terms of the curvature of spacetime caused by the presence of mass
Extensive vs. Intensive PropertiesIntensive properties do not change with
amount of substance; are used for identification» a. Examples: density, melting point,
boiling point, color, conductivityExtensive Property--depends on the amount
of matter present– b. These properties CANNOT be used to
ID the substance!!– a. ex: mass, volume, length …..
Physical vs. Chemical PropertiesPhysical Property--can be observed without
changing the identity of the substance» melting point- temp it changes from solid
to liquid » ductility- able to be pulled into a thin wire» Viscosity- how quickly or slowly a fluid
flows » solubility- will it dissolve in water
2. Chemical Property--These characteristics are observed ONLY when a substance changes into a different substance» a. examples of Chemical Properties
– 1) Combustible/flammable: able to burn
a) Examples & Facts: all chemicals come with a label that identifies their level of flammability
--oxygen & hydrogen are very flammable gases
--carbon dioxide is not a very flammable gas
C. Physical vs. Chemical Changes
» Physical Changes--change the form of a substance without changing its identity; properties remain the same
» Often reversible» Change of state most common
What are the Phase Changes?
s ℓ Melting
s g Sublimation
g ℓ Condensation
g s Deposition
ℓ g Evaporation
ℓ s Freezing
Chemical Changes--change the identity of a substance; products have new & different properties» Usually NOT reversible
Signs of a Chemical Change» a. change in color or odor» b. formation of a gas» c. formation of a precipitate formed (a precipitate is a solid product which forms in a chemical reaction)
4. Chemical Change examplesa. corrosion: slow reaction & wearing away of
metals (rusting, tarnishing)b. rusting- iron reacting with oxygenc. burning a log
Elements, mixtures and compounds
An element is defined as a substance that cannot be broken down into other substances by chemical means. The elements are listed on the periodic table.
A compound is formed when a number of these elements bond together. Compounds always have a fixed composition, i.e. they always contain the same definite amount of each element present in the compound;
for example, a water molecule always contains two hydrogen atoms bonded to an oxygen atom and has the formula H2O. If that composition is altered, the chemical formula changes and the substance ceases to be water
A mixture has varying composition and is made up of a number of pure substances. Mixtures can be;
(i) Homogeneous. Uniform in composition throughout a given sample but the composition and properties may vary from one sample to another; for example a solution of salt water,
(ii) Heterogeneous. Have separate, distinct regions within the sample. As a result the composition and properties vary from one part of the mixture to another; for example a chocolate chip cookie.
All pure substances are either elements or compounds.
Platinum
Separation of mixturesSeparation of MixturesFiltration – solid substances are separated
from liquids and solutions.Distillation – uses differences in the boiling
points of substances to separate a homogeneous mixture into its components.
Chromatography – separates substances on the basis of differences in solubility in a solvent.
Nature of Measurement
Part 1 - numberPart 2 - scale (unit)
Examples:20 grams
6.63 x 10-34 Joule·seconds
A measurement is a quantitative observation consisting of 2 parts:
SI Prefixes Common to ChemistryPrefix Unit Abbr. ExponentMega M 106
Kilo k 103
Deci d 10-1
Centi c 10-2
Milli m 10-3
Micro 10-6
Nano n 10-9
Pico p 10-12
Rules for Counting Significant Figures - Details
Nonzero integers always count as significant figures.
3456 has 4 sig figs.
Rules for Counting Significant Figures - Details
Zeros- Leading zeros do not count as significant figures.
0.0486 has3 sig figs.
Rules for Counting Significant Figures - Details
Zeros- Captive
zeros always count as significant figures.
16.07 has4 sig figs.
Rules for Counting Significant Figures - Details
ZerosTrailing zeros are significant only if the number contains a decimal point.
9.300 has4 sig figs.
Rules for Counting Significant Figures - Details
Exact numbers have an infinite number of significant figures.
1 inch = 2.54 cm, exactly
Sig Fig Practice #1How many significant figures in each of the following?
1.0070 m 5 sig figs17.10 kg 4 sig
figs100,890 L 5 sig figs
3.29 x 103 s 3 sig figs0.0054 cm 2 sig figs3,200,000 2 sig figs
Rules for Significant Figures in Mathematical Operations
Multiplication and Division: # sig figs in the result equals
the number in the least precise measurement used in the calculation.
6.38 x 2.0 =12.76 13 (2 sig figs)
Sig Fig Practice #2
3.24 m x 7.0 mCalculation Calculator says: Answer
22.68 m2 23 m2
100.0 g ÷ 23.7 cm3 4.219409283 g/cm3 4.22 g/cm3
0.02 cm x 2.371 cm 0.04742 cm2 0.05 cm2
710 m ÷ 3.0 s 236.6666667 m/s 240 m/s1818.2 lb x 3.23 ft 5872.786 lb·ft 5870 lb·ft
1.030 g ÷ 2.87 mL 2.9561 g/mL 2.96 g/mL
Rules for Significant Figures in Mathematical Operations
Addition and Subtraction: The number of decimal places in the result equals the number of decimal places in the least precise measurement.
6.8 + 11.934 =18.734 18.7 (3 sig figs)
Sig Fig Practice #3
3.24 m + 7.0 mCalculation Calculator says: Answer
10.24 m 10.2 m100.0 g - 23.73 g 76.27 g 76.3 g
0.02 cm + 2.371 cm 2.391 cm 2.39 cm713.1 L - 3.872 L 709.228 L 709.2 L1818.2 lb + 3.37 lb 1821.57 lb 1821.6
lb2.030 mL - 1.870 mL 0.16 mL 0.160 mL
Uncertainty in MeasurementA digit that must be estimated is called uncertain. A measurement always has some degree of uncertainty.
Measurements are performed with
instruments No instrument can read to an infinite number of decimal places
Precision and AccuracyAccuracy refers to the agreement of a particular value with the true value.Precision refers to the degree of agreement among several measurements made in the same manner.
Neither accurate
nor precise
Precise but not accurate
Precise AND
accurate
Accuracy & Precision• Consider 3 sets of data that have been
recorded after measuring a piece of wood that is exactly 6.000 m long.
• Which set of data is the most accurate?• Set Y
• Which set of data is the most precise?• Set Y
Set X Set Y Set Z5.864 m 6.002 m 5.872 m5.878 m 6.004 m 5.868 m
Average length
5.871 m 6.003 m 5.870 m
Review on your own…Review the notes on atomic theory and
know the major points, Dalton’s atomic theory, and the chart on experiments
Review calculations of P, N, E, atomic number, mass number and ions.
Review periodic table structure, know metals, non-metals and metalloids (semi)
Review ALL nomenclature, polyatomic ions, ionic compounds, covalent compounds, acids, oxoanions & oxoacids (we did oxoacids, we just didn’t label them as such)
Don’t forget stock system, hydrates, etc.