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Matter is anything that occupies space and has mass.

Unit 1-Chemistry and Measurement

Chemistry studies matter and the changes matter undergoes.

SugarWaterGold

Classifying MatterAll Matter

Pure Substances

Mixtures

Can it be separated by a physical

process?

CompoundsElements

YESNO

Can it be broken down into

simpler ones by chemical

means?

NO YES

1.6

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A mixture is a combination of two or more substances in which the substances retain their distinct identities.

1. Homogenous mixture – composition of the mixture is the same throughout.

2. Heterogeneous mixture – composition is not uniform throughout.

soft drink, milk, solder

cement, iron filings in sand

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The Three Physical States of Matter

solidliquid

gas

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A physical change does not alter the composition or identity of a substance.

A chemical change alters the composition or identity of the substance(s) involved.

ice meltingsugar dissolving

in water

hydrogen burns in air to form water

Change: Physical or Chemical?

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An extensive property of a material depends upon how much matter is is being considered.

An intensive property of a material does not depend upon how much matter is being considered.

• mass

• length

• volume

• density

• temperature

• color

Extensive and Intensive Properties

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International System of Units (SI)

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Uncertainty in Measurement: Significant Figures

• Every measurement includes some uncertainty. Measuring devices are made to limited specifications and we use our imperfect senses and skills.

• Significant figures: The digits we record in a measurement that include both certain digits and the first uncertain or estimated one.

• The number of significant figures in a measurement depends on the design or specifications of measuring device.

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Aspects of Certainty: precision and accuracy

Accuracy – how close a measurement is to the true value.

Precision – how close a set of measurements are to each other

accurate&

precise

precisebut

not accurate

not accurate&

not precise

Precision and Accuracy are linked to two common types of error:

• Random Errors – always occur. Random errors result in some values that are higher and some values that are lower than the actual value. These errors depend on the measurer’s skill and the instruments readability.

Precise measurements have low random error.• Systematic Errors occur due to poor experimental

design or procedure or faulty equipment.

Accurate measurements have low systematic error and low random error.

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Significant Figures in Measurements

• Any digit that is not zero is significant

1.234 kg 4 significant figures• Zeros between nonzero digits are significant

606 m 3 significant figures• Zeros to the left of the first nonzero digit are not

significant

0.08 L 1 significant figure• If a number is greater than 1, then all zeros to the right

of the decimal point are significant

2.0 mg 2 significant figures• If a number is less than 1, then only the zeros that are at

the end and in the middle of the number are significant

0.004020 g 4 significant figures

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How many significant figures are in each of the following measurements?

24 mL 2 significant figures

3001 g 4 significant figures

0.0320 m3 3 significant figures

6.4 x 104 molecules 2 significant figures

560 kg 2 significant figures

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Significant Figures in Calculations

Addition or Subtraction

The answer cannot have more digits to the right of the decimalpoint than any of the original numbers.

89.3321.1+

90.432 round off to 90.4

one significant figure after decimal point

3.70-2.91330.7867

two significant figures after decimal point

round off to 0.79

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Significant Figures in Calculations

Multiplication or Division

The number of significant figures in the result is set by the original number that has the smallest number of significant figures

4.51 x 3.6666 = 16.536366 = 16.5

3 sig figs round to3 sig figs

6.8 ÷ 112.04 = 0.0606926

2 sig figs round to2 sig figs

= 0.061

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Significant Figures

Exact Numbers

Numbers from definitions or numbers of objects are consideredto have an infinite number of significant figures

The average of three measured lengths; 6.64, 6.68 and 6.70?

6.64 + 6.68 + 6.703

= 6.67333 = 6.67

Because 3 is an exact number

= 7

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Scientific NotationThe number of atoms in 12 g of carbon:

602,200,000,000,000,000,000,000

6.022 x 1023

The mass of a single carbon atom in grams:

0.0000000000000000000000199

1.99 x 10-23

N x 10n

N is a number between 1 and 10

n is a positive or negative integer

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Scientific Notation is used to avoid ambiguity in the number of significant figures in calculations.Multiplication

1. Multiply N1 and N2

2. Add exponents n1 and n2

(4.0 x 10-5) x (7.0 x 103) =(4.0 x 7.0) x (10-5+3) =

28 x 10-2 =2.8 x 10-1

Division

1. Divide N1 and N2

2. Subtract exponents n1 and n2

8.5 x 104 ÷ 5.0 x 109 =(8.5 ÷ 5.0) x 104-9 =

1.7 x 10-5

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Scientific Notation Exercises568.762

n > 0

568.762 = 5.68762 x 102

move decimal left

0.00000772

n < 0

0.00000772 = 7.72 x 10-6

move decimal right

Addition or Subtraction

1. Write each quantity with the same exponent n

2. Combine N1 and N2 3. The exponent, n, remains

the same

4.31 x 104 + 3.9 x 103 =

4.31 x 104 + 0.39 x 104 =

4.70 x 104

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Density

1 g/cm3 = 1 g/mL = 1000 kg/m3

density = mass

volume d = mV

A piece of platinum metal with a density of 21.50 g/cm3 has a volume of 4.49 cm3. What is its mass? How many significant figures should the final answer have?

m = d x V = 21.50 g/cm3 x 4.49 cm3 = 96.5 g

21

Error and Uncertainty Analysis

Percent error = I theoretical – experimental I x 100%

Theoretical

Note: Numerator is an absolute value so that percent error is always positive

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Uncertainty Analysis

• Uncertainty should be reported to only one significant digit

• Proper 36.5 + 0.5 • Improper 36.5 + 0.25 • Fractional uncertainty = uncertainty

measurement

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Fractional uncertainties are often converted to percentage uncertainties by multiplying them by 100

• Rule 1: When adding or subtracting measurements the uncertainty of the result is the sum of the terms used

[36.8 + 0.1 cm] + [4.7 + 0.1 cm] = 41.5 + 0.2 cm

• Rule 2: When multiplying or dividing measurements, the fractional uncertainty in the result is the sum of the fractional uncertainties in the factors used

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Example: [41.7 + 0.1 cm] x [12.1 + 0.1 cm]

Fractional uncertainties:

0.1 / 41.7 = 0.002 , 0.1 / 12.1 = 0.008

Product: 41.7 cm x 12.1 cm = 505 cm2

Uncertainty: 0.002 + 0.008 = 0.01

0.01 x 505cm2 = 5cm2

Answer: 505 + 5cm2Dura GOB 25

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