The Scientific Method

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The Scientific Method
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What is chemistry?

• The study of matter, its structure, properties,
  and composition, and the changes it undergoes.

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How do scientists approach problems?

• Pure science science that seeks to gain
  knowledge
• Applied science science that seeks to solve a
  problem
• Also known as technology

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What is scientific knowledge based upon?

• Scientific knowledge is based on observations
• These observations lead to asking questions
• Problems are solved using the scientific method

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What is the scientific method?

• A logical approach to the solution of a problem
  or question that has been raised through
  observation

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What are the steps in the scientific method?

• Make observations about a phenomenon
• State a problem based on observations made
  (usually in the form of a question)
• Research
• Form a hypothesis
• Test the hypothesis using an experiment
• Collect data
• Analyze and interpret the data
• State conclusions

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Step 1

• Make observations about a phenomenon
• Qualitative Do not involve numbers
• Chemical and Physical Properties
• Quantitative Involve numbers with units

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Step 2

• State a problem based on observations made
  (usually in the form of a question)

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Step 3

• Form a hypothesis after doing some research
• A reasonable explanation for an observed
  phenomenon

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Step 4

• Test the hypothesis using an experiment and
  collect data
• A process carried out under controlled conditions
  to test the validity of a hypothesis
• Parts of an experiment
• Constant factors that remain the same during
  the experiment
• Control responds in a predictable way to the
  experiment
• Variables factors that change during the
  experiment

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Step 4 continued

• Analyze and interpret the data
• Charts
• Graphs
• Observations should be made objectively

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What are the two types of variables?

• Independent factors the experimenter has control
  over (manipulated factors)
• Dependent factors that change as a result of a
  change in the independent variable (responsive
  factors)

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Step 5

• State conclusions
• theory a logical and time-tested explanation of
  experimental observations
• Examples cellular theory, atomic theory,
  molecular theory, evolutionary theory, the theory
  of plate tectonics, the theory of relativity,
  gravitational theory
• law a logical explanation of phenomenon that
  occurs in the natural world
• also called a rule of nature, example Newtons
  Law of Motion

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Graphing

• What features should every graph have?
• The scale must be appropriate for the amounts
  being graphed so as to best utilize the space
• The scale should be correctly proportioned
• The graph must fill the entire sheet of paper
• The independent variable should ALWAYS be on the
  x-axis

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Graphing

• Title
• Clearly labeled x- and y-axes, with name of
  variable AND units
• Points plotted with small points, not large
  circles
• Best-fit line through the points
• Legend if more than one line is drawn on the
  graph

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Metric System

• International system of measurement
• 7 base units
• Length meter (m)
• Temperature Kelvin (K)
• Mass kilogram (kg)
• Time seconds (s)
• Amount of substance mole (mol)
• Electric current ampere (A)
• Luminous intensity candela (cd)

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Units

• Derived units Combination of units
• Non SI units in chemistry
• Volume liter (L)
• Energy calorie (cal)
• Pressure atmosphere (atm), Pascals, mm of Hg
• Temperature celsius (C)

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Metric Prefixes

• pico(p) 10-12 deka(D) 10
• nano(n) 10-9 Hecto(H) 102
• micro(µ) 10-6 kilo(k) 103
• milli(m) 10-3 Mega(M) 106
• centi(c) 10-2 Giga(G) 10 9
• deci(d) 10-1
•  BASE

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How Reliable Are Measurements?

• No measurement obtained in the lab is exact ALL
  measurements have some error
• Sources
• Instrumental error instrument not calibrated
  correctly
• Human error occur by chance or through bias
• Method error incorrect procedure or poor design
  of experiment

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Accuracy and Precision

• Precision degree of exactness or refinement of
  a measurement
• Accuracy how close a measurement comes to the
  true accepted value
• both are terms to describe error
• two types of measurement error
• random errors measurement have equal
  probability to be too high or too low
• also called indeterminant error
• occurs when estimating the uncertain digit

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Accuracy and Precision

• systematic errors measurement errors that occur
  in the same direction
• measurements are either always too high or too
  low
• also called determinant errors
• when reporting errors you must be very specific
  about the error
• Because measurements differ in precision, when
  calculation are performed, significant digits
  MUST be taken into consideration

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Significant Figures

• each piece of equipment can measure to varying
  degrees
• the measurement obtained from a particular piece
  of equipment containing all the certain digits
  and one uncertain digit is called a significant
  figure

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Rules for Significant Figures

• All nonzero digits are significant (1-9)
• Zeros are significant if
• a. between nonzero digits (captive zeros)
• b. to the RIGHT of a decimal point AND also to
  the RIGHT of a nonzero digit (trailing zeros)
• c. a line is drawn over it
• d. if a decimal point is expressed (exact numbers)

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What are the Rules for Basic Operations Using Sig
Figs?

• Addition and Subtraction
• Round answer to the least number of decimal
  places in any of the numbers that make up the
  answer
• Example 18.31112 32.728
• Example 86.432 - 10.

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What Are the Basic Rules for Multiplication and
Division?

• Round to the least number of significant figures
  in any of the factors
• Example 48.2 x 1.6 x 2.12
• Example 16.4/4.1
• Example 3 x 42.59 x 16.5
• Example 15.535/2

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Scientific Notation

• A number expressed as the product of two factors
• The first number is between 1 and 9
• The second number is a power of ten
• Uses only the sig figs of the original number
• Exponent found by counting the number of times
  the decimal point must be moved to make the first
  number between 1 and 9 ( value gt1, - value lt 1)
• Examples 120000 1.2 x 105
• 1405000
• 750670000
• .000457

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Error

• Method of evaluating the accuracy of a
  measurement
• Ratio of error to an accepted value
• Formula
• Error Measured Value - Accepted Value x
  100
• Accepted
  Value

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Dimensional Analysis

• A method of converting from one measurement to
  another using conversion factors
• conversion factor fraction of equivalent values
  to express the quantity in different ratios
• Always equal to one
• Examples
• 1 dozen doughnuts 12 doughnuts
• 1 dozen doughnuts 1
• 12 doughnuts

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To Use Dimensional Analysis

• Read problem
• Determine what you are starting with and what you
  are looking for
• Set up problem with what you are looking for
• Set that equal to what you are staring with

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Example

• How many seconds are there in 52 years?
• Seconds is what you are looking for
• 52 years is what you are starting with
• ? Seconds 52 years
• Now, use conversion factors
• ? Seconds 52 years x 365 days x 24 hours x 60
  minutes x 60 seconds ?
• 1 year 1 day 1 hour 1 minute

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DA Examples

• Convert 15 mm to m
• Convert 50 L to mL
• Convert 32 in to m