Measurement andSignificant Figures

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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 solving

1. Observations- quantitative (involve #’s

or measurement)- qualitative ( don’t invole

#’s)2. Formulating hypothesis

- possible explanation for the observation

3. 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 problem

A 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 Properties

Intensive 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 examples

a. 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:

Celsius & Kelvin

SI Prefixes Common to Chemistry

Prefix 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 figs

17.10 kg 4 sig figs

100,890 L 5 sig figs

3.29 x 103 s 3 sig figs

0.0054 cm 2 sig figs

3,200,000 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 m

Calculation 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/s

1818.2 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 m

Calculation Calculator says: Answer

10.24 m 10.2 m

100.0 g - 23.73 g 76.27 g 76.3 g

0.02 cm + 2.371 cm 2.391 cm 2.39 cm

713.1 L - 3.872 L 709.228 L 709.2 L

1818.2 lb + 3.37 lb 1821.57 lb 1821.6 lb

2.030 mL - 1.870 mL 0.16 mL 0.160 mL

Uncertainty in Measurement

A 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 Z

5.864 m 6.002 m 5.872 m

5.878 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.