Unit 1: Back to the Basics

Section 1: Basic Principles

* Introduction
* Scientific Method
* Units of Measurement
* Confusing Words In Chemistry
* Significant Figures
* Key Concepts
* Mixtures

Introduction

Chemistry is a subdivision of science and it specializes in the composition,
structure, and properties of substances and the transformations in which
these substances go through. This might sound confusing to some, but really
it is quite simple to understand. Chemistry can be found all over the world,
even in such basic things as cooking. For instance, when you boil water,
Chemistry explains why water evaporates and why salt will dissolve in it.
Basically, Chemistry studies chemicals (hence the name Chemistry) and
applies this knowledge to modern society. To understand how to apply the
Chemistry knowledge, you must first understand the basic principles behind
Chemistry.

Scientific Method

In all sciences, there is a system that describes how to go about solving
problems. This system is called the Scientific Method. Basically, there are
four parts to this system, that are very logical in order. First, an
observation must be made. Observations can be either in the form of
quantitative observations or qualitative observations. Quantitative
observations have to do with numbers, whereas qualitative observations have
to do with a physical characteristic of something. For example, the observer
observes a two winged red butterfly. The fact that the butterfly has two
wings is a quantitative observation and the fact that the wings are red is a
qualitative observation. This leads to the second part of the scientific
method. After making many observations, the observer formulates a question,
which is normally, why did that happen? From there, the observer looks for
possible reasons why, or what is called formulates theories. A theory is the
observer's interpretation of the data that he has collected. The first set
of theories is called a hypothesis. A hypothesis is simply an educated guess
on the part of the observer to explain the question at hand. The fourth and
final step is for the observer to test his theory by experimentation. If the
theory is wrong the observer goes back and formulates a new theory, and if
he is right, he goes back and retests his theory.

Science is in no way perfect. People do make mistakes, this is part of the
human nature, but as technology improves and more people test the previous
theories, the wrong ones get sorted out from the right ones and science
corrects itself.

Units of Measurement

In science and chemistry, measurements are very important. Measurements are
quantitative observations. An example of a measurement is that the desk is 4
feet long. Measurements in science pose a big problem to its users. This is
true because there are two different systems in use. Americans use a system
called the English system. The English system uses units like inches, feet,
gallons, and miles, and there is no easily remembered relationship between
the units, so a world-wide system of measuring was established called the
Metric System, or SI system. This system is based on multiples of ten. For
example, if you have 1 meter, you have 100 centimeters, 1000 millimeters,
and .001 kilometers. This is obviously easier to understand.

Prefix Symbol Meaning Exponential Notation

mega M 1,000,000 106

kilo k 1,000 103

hecto h 100 102

deka da 10 101

----- ----- 1 100

deci d .1 10-1

centi c .01 10-2

milli m .001 10-3

micro u .000001 10-6

In the SI system, there are base units for measurement. Examples of these
units are meter for length, liter for volume, and gram for mass. What makes
this system even easier than the English system is that the prefixes are
standard for all the base units. So if you have a kilogram of water, you
have 1000 grams of water and if you have a kilometer of road, you have 1000
meters of road.

It is important to understand that in science, when you take measurements
the last number is always estimated. For example, if the ruler you were
using to measure a piece of paper was calibrated to centimeters (meaning the
smallest marked units were centimeters) and the length came out to 20
centimeters, this answer would not be acceptable because the answer has to
have an uncertain value which would be the millimeter's value. (Measurements
must always be one decimal place more exact than the smallest marked units
on the measuring device.) In the example above, 20.0, 20.3, or 19.8 would
all be acceptable values.

Confusing Words In Chemistry

In the beginning of Chemistry, there are always a few terms which must be
defined because their definitions are very close to each other or are
important. One of the most general words in Chemistry is matter. It is
important to understand matter because everything in the universe is made up
of matter. Matter can exist in three phases, solid, liquid, and gas.
(Plasma)Solids are rigid structures which have definite volume and definite
shape. Due to the strength of solids, they are not easily compressed.
Liquids are the second state of matter that matter can exist in. Liquids
have definite volume, but lack definite shape. This is why liquids will fill
containers with odd shapes, but are not easily compressible. Gases are the
third and final state in which matter can exist in. Gases do not have
definite volume and do not have definite shape and this is why they will
fill containers with odd shapes and are easily compressible.

The first set of words that might pose a problem to a beginner in Chemistry
is mass and weight. In today's society, mass and weight may be used
interchangeably, but in Chemistry they are very different. Mass is the
amount of matter that an object has. An example of the difference between
mass and weight is that a person on earth may have a mass of 220 kilograms
but weigh 100 pounds and on the moon that same person will have a mass of
220 kilograms and weigh 16.7 pounds. The reason why the weight changed was
because the moon's gravitational pull is much less than earth's, but take
note to the fact that the mass never changes no matter what the weight does.

Another set of words that must be defined is precision and accuracy. Once
again, these words are very easily interchanged in today's society, but in
Chemistry they have very different meanings. Precision refers to how close
the values are to each other. Accuracy is how close the values are to the
true value.

To understand precision and accuracy more, lets assume that three student
wants to find out what the boiling temperature of water is. We all know that
water boils at 100 degrees Celsius, so this is our true value. Below are the
results of the three trials of the three students.

 

 

Student 1 Student 2 Student 3

Trial 1 102.5 102.6 100.4

Trial 2 95.6 102.5 100.0

Trial 3 99.4 102.4 100.2

 

 

Student 1's results were obviously all over the place, so he was neither
accurate nor precise. Student 2's results were all very close together which
means that his results were precise, but all his results were not close to
100 so, his results were not accurate. On the other hand, Student 3's
results were both close together and close to 100, so his results were both
precise and accurate.

In Chemistry, there are two main types of error. One is called systematic
error. This type of error occurs when the values that are found are
consistently high or consistently low. An example of why systematic error
might occur is that a thermometer might be miscallibrated. (Student 2, the
example above had systematic error.) The other type of error is random
error. This type of error occurs when the chances of being high or being low
are equal. For example, if you throw five darts at a dartboard, you have
equal chance of being high or low. (Student 1, in the example above had
random error.)

Significant Figures

One of the most tedious parts of Chemistry is Significant Figures, or more
commonly called Sig Fig's. Have you ever heard someone say that a chain is
only as strong as its weakest link? This is what happens with Sig Fig's. An
answer can only be as exact as its least exact number , so if two and two
are multiplied together the answer is obviously four, but what if you
measured one value at 4.1 (remember that .1 is estimated) and multiplied it
by another value that you measured at 5.526? The answer can't be 22.6566,
because how can you have your answer more exact that the least exact value
that you have. Because 4.1 is the least exact value, the final value can
only be 23 because of the rules that the scientific community came up with
to deal with this problem called the Rules of Sig Fig's.

TRY IT FOR YOURSELF: Practice Problems

Key Concepts

Temperature, in Chemistry, plays many important roles, especially in solving
equations. There are three main units in which temperature can be written
in. They are Kelvin, Celsius, and Fahrenheit. Fahrenheit is one of those
American units which are not often used in the scientific community. Celsius
is the most used unit of temperature in Chemistry, but many formulas require
temperature in them, and when computing formulas, Kelvin is more often used.
Because each unit has its own reason for being used, it is important to
understand how Kelvin is related to Celsius. The formulas for converting
Kelvin temperature to Celsius temperature and vice versa, are as follows:

Temp(Kelvin) = Temp (Celsius) + 273

Temp(Celsius) = Temp (Kelvin) - 273

Another very important value in Chemistry is density. Density is a ratio of
mass to volume. For every substance at a certain temp, and pressure there is
only one unique density value. This value is the same no matter how much or
how little of the substance is used. Density can be used to determine what
certain substances are. For example, if there is a substance which has a
density of 1.00 g/mL, a chart of densities can be used to show that the
unknown substance is water.

Mixtures

In Chemistry and the real world, substances are not always pure. Pure
substances are substances that have constant composition. Mixtures are
substances or a group of substances which are variable in composition and
can be separated by physical means. An example of a mixture might be sand
and gravel. There are two types of mixtures. One type is a homogeneous
mixture. In this type of mixture, the substance is the same through out. The
second type of mixture is heterogeneous. A heterogeneous mixture is a
mixture containing regions of different properties. An example of
heterogeneous mixture is when you take a bucket of water and dump dirt in
it. Some of the dirt stays suspended in the water while most of the dirt
falls to the bottom, creating regions of different properties.

We defined pure substances (in the previous paragraph) as substances that
have constant composition, and because of this, pure substances can be
broken down into small groups called compounds and elements. A compound is a
substance with constant composition which can be broken down into its
elements by chemical processes. Chemical processes are processes where the
atoms in a substance are reorganized to form a new substance. After
substances are broken down into its basic elements, elements can no longer
be broken up. [Please note that physical processes can be reversed, such as
filtration, but chemical processes can not, such as combustion.]