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Chem101

Chapter 01

Chemical Foundations

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What is chemistry?

A key concept is that chemists look for explanations

how materials may be analyzed at the atomic and molecular level (Macroscopic & Microscopic.

The science that explains:

the properties of materials

how new materials may be made

the relationship between energy and chemical reactions

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1.1Chemistry: An overview

• Chemistry is fundamentally concerned with: "How one substance changes to another"1. How plants grow by absorbing water and Carbon

dioxide?2. How humans manufacture the proteins from the

food we consume? 3. ….. and on and on

• A substance is composed of atoms, all universe is made of only 110 {different types of atoms}

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1.2 The Scientific Method

It is a systematic approach to research that includes:

– Making Observation– Making a Prediction "Hypothesis"– Doing Experiment to test the

Hypothesis

Law: summary of observed behavior

Theory: model attempt to explain

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1.3 Units of MeasurementQuantitative Measurement, consists of two parts:

a numbernumber and a scalescale (unit)

• In 1960, an international agreement get up a system of units called International System (SI- system) based on metric system.

Quantity Unit Abreviation Mass Kilogram Kg Length Meter m Time Second s Temperature Kelvin k Current Ampere A Amount oh sub Mole Mol Luminous int. Candela cd

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Prefixes: are used to change the size of the unit

Table 1.2 Prefixes Used with SI Units

Prefix Symbol Meaning

Tera- T 1012

Giga- G 109

Mega- 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

1.3 Units of Measurement

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• Volume is not fundamental SI – unit, but very commonly used in chemistry,

{SI derived unit for volume is cubic meter (m3)}

Used unit in liter = 1dm3

1 m3 = (10 dm)3 = 1000 dm3 = 1000 L

1 L = 1dm3 = (10 cm)3 = 1000 cm3 (ml)

1.3 Units of Measurement

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1.4 Uncertainty in measurement Any measurement always has some degree of

uncertainty. Uncertainty depends on the precision of measuring device.

e.g., measurement of volume of a liquid using a buret:

• the used liquid is about ………………….mL

If 4 different people read the same volume we might get:

Person Result

1 22.2

2 22.1

3 22.3

4 22.0

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1.4 Uncertainty in measurement • You have to record the certain digits and

the first uncertain digit only.• All digits together

[ certain + first uncertain]

are called

" Significant Figures"• The uncertainty in the last number must

be assumed to be # 1

Volume = 22.2 ± 0.1 mlExample 1.1:

What is the difference between the measurements 25.00mL and 25mL?

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Precision and Accuracy• Accuracy: it is the

agreement of a particular value with the true value.

• Precision: it is the agreement among several measurements of the same quantity.

1.4 Uncertainty in measurement

Not AccurateNot precise

Not AccurateBut precise

Accurateand precise

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Errors• Random error: it means that

a measurement has an equal probability of being high or low.

• Systematic error: error accurse in the same direction each item.

1.4 Uncertainty in measurement

Large Random Error

Small Random and Large Systematic Error

Small Random And NO Systematic Error

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1.5 Significant Figures (SF) and Calculations

Rules for Counting Significant Figures:It is important to be applied to get the uncertainty in the final results out of adding, subtracting multiplying ..etc.

• Nonzero integers, count as SF.• Zeros:

- "Leading zeros” are not significant. e.g. 0.0025 (2 SF) - "Captive zeros” Count as s.f. e.g.: 1.008 (4 SF)

- "Trailing zeros” count as s.f. eg. : 100 = 1.00 X 102 (3 SF)

• Exact numbers have an infinite number of SF e.g. 10 experiment, 5 apples, 8 books … so on. ..

• Exponential notation: it is used to unite large or small numbers in the correct sig.fig.

e.g. 0.000060 convenient 6.0 x 10-5

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Rules for SF in Mathematical Operations: • Multiplication / Division: Final results have the

same SF in the least precise measurement used in calculation.

e.g. 4.56 x 1.4 = 6.38 = (………………?)• Addition / Subtraction: Final results have

the same number of decimal places as the least precise numbers

e.g. 12.11 + 18.0 + 1.013 = 31.123 = (…………?)

1.5 Significant Figures (SF) and Calculations

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Note: To get the correct total SF in the final results you may round off the results.

Rules for rounding:if the number to be removed is < 5, the preceding digit stays the same.

e.g., round 1.33 to 2 S.F. (…………?)Exercise 1.4:

a) 1.05 x 10-3 ÷ 6.135 = (………….?)

b) 21 – 13.8 = (……………?)

1.5 Significant Figures (SF) and Calculations

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1.6 Dimensional Analysisconversion of a given results from one system unit to an other using "Unit Factor Method" or dimensional analysis.

Means Multiply any expression by "1" will not change its value.

• Exercise 1.5:A pencil is 7.00 in long, What is its length in centimeter?

– Solution: • what is the in/cm relation: 2.54cm = 1 in• which unit is needed: cm• unit factor must has cm unit as nominator.

i.e. 2.54 cm / 1 in = 1 [unit factor]Multiply the length by the unit factor gives: 7.00 in x 2.54 cm /1 in = 17.8 cm

7.00 in = 17.8 cm

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Note:

Sometime you have to do multi-step conversion to get correct answer.

Exercise 1.7:

A student has entered a 10.0 km race. How long is the run in miles?

• Solution: km m yd mi [1 km = 1000m, 1 m = 1.09yd, 1760yd = 1 mi]

• Results: 10.0 km = 6.22 mi

1.6 Dimensional Analysis

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1.7 TemperatureEngineeringScience

DifferenceIs complicated

DifferenceIs in their zero

Conversion1. Adjustment in the degree step2. Adjustment in the zero

ConversionAdjust the zero difference

Tc = (TF-32oF) x 5oF/ 9oC TF = (T0C x 9oF/5oC) + 32oF

T(Kelvin) = T(oC) + 273.15

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1.8 DensityIt is the mass per unit volume of the substance.

A property of matter that is often used by chemists.

Density =

Chloroform 1.492 g / cm3 At 20oC

Diethyl ether 0.714 g / cm3 At 20oC

Ethanol 0.789 g / cm3 At 20oC

Isopropyl alcohol

0.785 g / cm3 At 20oC

Toluene 0.867 g / cm3 At 20oC

Exercise 1.13:A chemist finds that 25.00cm3

of a CD- cleaner has a mass of 19.625g at 20oC.

The following are the names and densities of the compounds that might be the main component:

Which of them is the most likely to be the main component of the CD-cleaner?

Solution:

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1.9 Classification of matter

Read (pp. 26-30)

and Report (HW#2):

• Define :"Matter, Mixtures, Physical

changes, Compound, and Element"

• Define:"Distillation, Filtration, and

Chromatography.

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