Chemistry: The Study of Change

Chapter 1Dr. Ali Bumajdad

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Chapter 1 Topics

Dr. Ali Bumajdad

• The Scientific Method•Units, Prefix, and Unit Conversion•Accuracy, Precision and Significant Figure•Temperature Scales•Density•Matter, Mixtures and separation methods•Physical and Chemical change•Extensive and Intensive properties

Introduction

•The Scientific method: Overall philosophy of approach to the study of nature.

observation Law Statements of fact often in equation form

Hypotheses tentative explanation of experiments results

Theorytested explanation of experiments results

quantitativenumbers

concentration

qualitativeno numbers2Na + Cl2 2NaCl

• Note that theory is not fact and it could be wrong but we need to proof it.

The Scientific method

Units, Prefix, and Unit Conversion

• SI-Derived Unit

Area = m2

Volume = m3

Speed = m/s

• Unit conversion

Usually we use 1) Factor-label method : units undergo the same kind of mathematical operation as numbers

2) Conversion Factor: a fraction that we use to change the units

Accuracy, Precision and Significant Figure

Accuracy – how close a measurement is to the true value :A -TRUE

Precision – how close a set of measurements are to each otherP - EACH

accurate&

precise

precisebut

not accurate

not accurate&

not precise

1 L = 1000 mL

e.g. How many mL are in 1.63 L?

1L1000 mL

1.63 L x = 1630 mL

e.g. The speed of sound in air is about 343 m/s. What is this speed in miles per hour?

1 mi = 1609 m 1 min = 60 s 1 hour = 60 min

meters to miles seconds to hours

• Sig. Fig.

1) Nonzero digits always count as S. F.

2) Zeros between nonzero always count as S.F.

3) Zeros to the left of the first nonzero digit not count as S.F.

4) Zeros at right end of numbers significant only if there is a decimal point

5) For and , the no. of S. F. in the result = the least no. of S. F. used in the operation

6) For + and -, the no. of decimal places in the result = the least no. of decimal places in the operation

7) If the first digit after the S. F. is < 5, drop the digits that follow the S.F. numbers.

6) If the first digit after the S. F. is ≥ 5, drop the digits that follow the S.F. numbers and add 1 to the last digit

7) Exact numbers ( numbers contain no uncertainty) are not considered in the calculating of S. F.

Sig. Fig. = important numbers

important numbers = all the number I am sure about it + one estimated number

e.g. 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

e.g. Addition or Subtraction89.3321.1??+

90.432 round off to 90.4One decimal place (one significant figure after decimal point)

3.70??-2.91330.7867

two decimal places

round off to 0.79Multiplication or Division

4.51 x 3.6666 = 16.536366 = 16.5

6.8 ÷ 112.04 = 0.0606926 = 0.061

e.g. Exact NumbersNumbers from definitions or numbers of objects are consideredto have an infinite number of significant figures

e.g. 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

Sa Ex. 1.4: Write the answer with te correct Sig. Fig.

a) (1.05 × 10-3) ⁄ 6.135 = 1.71149 × 10-4 = 1.71 × 10-4 b) 21 – 13.8 = 7.2 = 7

C) P V/T , where P = 2.560, T= 275.15, V = 8.8= 0.0818753 = 8.2 × 10-2

Temperature Scales

TK = TC+ 273.15

TC = TK – 273.15 TC = (TF – 32) 59

TF = (TC 9 ) + 325

e.g. Convert 172.9 0F to degrees Celsius.

TC = 78.3 0C

Sa. Ex. 1.12 Liquid nitrogen boil at 77.0 K convert to Fahrenheit.

TF= -321 0F

Density

SI derived unit for density is kg/m3

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

density = mass

volume d = mV

e.g. A piece of platinum metal with a density of 21.5 g/cm3 has a volume of 4.49 cm3. What is its mass?

d = mV

m = d x V = 21.5 g/cm3 x 4.49 cm3 = 96.5 g

Matter, Mixtures and Separation methods

A Matter any thing occupies a space and has a mass

Three States

solidliquid

gas

mixture composition is constant

mixture composition not constant

substance with constant composition that can be broken down into elements by chemical process

ORTwo or more different atoms bind together by a chemical bond

substance that can not be decompose into simpler form by chemical or physicalchange

What is the different between element and atom?

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

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

Physical methods can be used to separate a mixture into its pure components.

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

Physical and Chemical change

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 is being considered.

• mass

• length

• volume

• density

• temperature

• color

•Extensive and Intensive properties