Chemical Foundations

1
Chemical Foundations

• Chapter 1

2
Chemistry

• Chemistry deals with situations in which the
  nature of a substance is changed by altering its
  composition so that entirely new substances are
  synthesized or particular properties of existing
  substances are enhanced.

3
Science

• Science is both a noun and a verb.
• Science is a body of knowledge and a method of
  adding to that body of knowledge.

4
Steps in the Scientific Method

• 1. Observations
• - quantitative - measurement involves a
  number and a unit.
• -? qualitative
• 2. Formulating hypotheses
• -? possible explanation for the observation
• 3. Performing experiments
• -? gathering new information to decide
• whether the hypothesis is valid

5
Outcomes Over the Long-Term

• Theory (Model)
• -? A set of tested hypotheses that give an
• overall explanation of some natural phenomenon.
• Natural Law
• - The same observation applies to many
• different systems
• - ?Example - Law of Conservation of Mass

6
Law vs. Theory

• A law summarizes what happens
• a theory (model) is an attempt to explain why it
  happens.

7
The various parts of the scientific method.
8
Problems of the Scientific Method

• Scientists must be objective when using the
  scientific method. The scientific method is
  affected by
• profit motives religious beliefs
• wars misinterpretation of data
• budgets emotions
• fads prejudices
• politics peer pressure

9
Nature of Measurement

• Measurement - quantitative observation
  consisting of 2 parts
• Part 1 - number
• Part 2 - scale (unit)
• Examples
• 20 grams
• 6.63 ? ????? Joule seconds

10
International System(le Système International)

• Based on metric system and units derived from
  metric system.

11
The Fundamental SI Units
12
(No Transcript)
13
One liter is defined as a cubic decimeter and 1
mL is one cubic centimeter.
14
Common types of laboratory equipment used to
measure liquid volume.
15
Mass Weight

• Mass is a measure of the resistance of an object
  to a change in its state of motion -- a constant.
• Weight is the measure of the pull of gravity on
  an object and varies with the objects location.

16
Uncertainty in Measurement

• A digit that must be estimated is called
  uncertain. A measurement always has some degree
  of uncertainty.

17
Measurement of volume using a buret. The volume
is read at the bottom of the meniscus.
18
Precision and Accuracy

• Accuracy refers to the agreement of a particular
  value with the true value.
• Precision refers to the degree of agreement
  among several elements of the same quantity.

19
a) is neither precise nor accurate, b) is precise
but not accurate (small random, large systematic
errors) c) both precise and accurate (small
random, no systematic errors.
20
Types of Error

• Random Error (Indeterminate Error) - measurement
  has an equal probability of being high or low.
• Systematic Error (Determinate Error) - Occurs in
  the same direction each time (high or low), often
  resulting from poor technique.

21
Accuracy

• Sample Exercise 1.2 on page 13.
• Trial Graduated Cylinder Buret
• 1 25 mL 26.54 mL
• 2 25 mL 26.51 mL
• 3 25 mL 26.60 mL
• 4 25 mL 26.49 mL
• 5 25 mL 26.57 mL
• Average 25 mL 26.54 mL
• Which is more accurate?
• Graduated cylinder produces systematic error
  --value is too low.

Buret
22
Exponential Notation

• Also called scientific notation and powers of ten
  notation. Exponential notation has two
  advantages
• the number of significant digits can easily be
  indicated
• fewer zeros are needed to write a very large or
  very small number.

23
Rules for Counting Significant Figures - Overview

• 1. Nonzero integers
• 2. Zeros
• - leading zeros
• - captive zeros
• - trailing zeros
• 3. Exact numbers

24
Rules for Counting Significant Figures - Details

• Nonzero integers always count as significant
  figures.
• 3456 has
• 4 sig figs.

25
Rules for Counting Significant Figures - Details

• Zeros
• - Leading zeros do not count as
• significant figures.
• 0.0486 has
• 3 sig figs.

26
Rules for Counting Significant Figures - Details

• Zeros
• - Captive zeros always count as
• significant figures.
• 16.07 has
• 4 sig figs.

27
Rules for Counting Significant Figures - Details

• Zeros
• -? Trailing zeros are significant only
• if the number contains a decimal point.
• 9.300 has
• 4 sig figs.

28
Rules for Counting Significant Figures - Details

• Exact numbers have an infinite number of
  significant figures. Can come from counting or
  definition.
• 15 atoms
• 1 inch 2.54 cm, exactly

29
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 ? 2.0
• 12.76 ? 13 (2 sig figs)

30
Rules for Significant Figures in Mathematical
Operations

• Addition and Subtraction sig figs 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)

31
Rules for Rounding

• 1. In a series of calculations, carry the extra
  digits through to the final result, then round.
• 2. If the digit to be removed
• a. is less than five, the preceding digit stays
  the same.
• b. is equal to or greater than five, the
  preceding digit is increased by 1.

32
Dimensional Analysis

• Also called unit cancellation is a method of
  solving problems by using unit factors to change
  from one unit to another.
• Unit factor -- the unit that you have goes on
  bottom, and the unit that you want goes on top.

33
Dimensional Analysis
Proper use of unit factors leads to proper
units in your answer.
34
Dimensional Analysis

• What is the dimension of a 25.5 in bicycle frame
  in centimeters?
• (25.5 in)(2.54 cm/1 in) 64.8 cm
• Units must be cancelled and the answer must have
  correct sig figs, be underlined, and include
  proper units!!

35
Temperature

• Celsius scale ??C
• Kelvin scale K
• Fahrenheit scale ??F

36
Three major temperature scales.
37
Temperature
38
Temperature Calculations

• Convert - 40.0 oC to Kelvin.
• K C 273.15
• K -40.0 273.15
• K 233.2 K

39
Temperature Calculations

• Convert - 40.0 oC to Fahrenheit.

100 F - 3200 -7200 100 F -4000 F -
40.0 oF
40
Density

• Density is the mass of substance per unit
• volume of the substance

41
Density Calculations

• If an object has a density of 0.7850 g/cm3 and a
  mass of 19.625 g, what is its volume?

V 25.00 cm3
42
Matter Anything occupying space and having
mass.
43
Classification of Matter

• Three States of Matter
• Solid rigid - fixed volume and shape
• Liquid definite volume but assumes the shape
  of its container
• Gas no fixed volume or shape - assumes the
  shape of its container

44
Types of Mixtures

• Mixtures have variable composition.
• A homogeneous mixture is a solution (for
  example, vinegar)
• A heterogeneous mixture is, to the naked eye,
  clearly not uniform (for example, a bottle of
  ranch dressing)

45
HOMOGENEOUS MATTER

• - a substance with the same properties throughout
  -- a pure substance.
• Elements and compounds are pure substances
  (homogeneous matter).

46
HETEROGENEOUS MATTER

• - has different properties throughout -- a
  mixture.
• Salt and pepper
• soil
• granite
• sea water
• spaghetti meat balls

47
SEPARATION OF MIXTURES

• - mixtures can be separated into pure substances
  by physical means.
• distillation
• filtration
• centrifuging
• magnet
• evaporation
• chromatography

48
Simple laboratory distillation apparatus.
49
CENTRIFUGE
50
(No Transcript)
51
Paper Chromatography
Chromatography has two phases of matter a
stationary phase (the paper) and a mobile phase
( the liquid).
52
Compounds Elements
Compound A substance with a constant
composition that can be broken down into elements
by chemical processes.

• Element A substance that cannot be decomposed
  into simpler substances by chemical means.

53
Universe
Matter
Energy
Physical Change
Homogeneous
Heterogeneous
Potential Energy
Kinetic Energy
Solution
Mixture
Pure Substance
Position
Composition
Chemical Change
Element
Compound
Gravitational
Electrostatic
Electron Levels
Nucleus
Protons
Neutrons
Electrons
54
TO BUILD FROM MATTER IS SUBLIMELY GREAT, BUT
GODS AND POETS ONLY CAN CREATE.

• Pitt