DelTech chemistry 100 and chemistry 110 with Dr. Marc Taylor.
unit 1 chemistry and measurements
introduction to the scientific method
today we're going to cover some key
terms definitions of chemistry itself
matter significant figures also known as
significant digits or sig figs for short
conversion factors which are part of a
concept known as dimensional analysis
we'll talk about terms associated with
the scientific method terms like
hypothesis law and theory and we'll talk
about the differences between accuracy
and precision many of these words are
used in the same way in everyday
colloquial English such as hypothesis
and theory or accuracy and precision but
in science these know these names mean
something very different so we'll talk
about the scientific method in another
unit we'll talk about scientific
notation accuracy and precision units of
measurement and the metric system
we'll talk about measured numbers and
sig figs will talk about sig figs in
calculations and how to round them
properly we'll talk about both the
metric system and the International
System known as the SI system which is
closely related to the metric system
we'll talk about conversion factors and
how they're used in dimensional analysis
and we'll talk about how density is
calculated based on mass and volume and
the definition of specific gravity so
let's talk about some definitions theory
theory is a well-established hypothesis
we have the theory of natural selection
the Big Bang Theory cell theory these
are all theories to a scientist and and
what we mean by theory and as a
scientist is that these were ideas that
were passed and postulated for how
something happens and these ideas were
tested over and over again sometimes
thousands or even tens of thousands of
times in different experiments and every
experiment supported this original
hypothesis so we now call it a theory we
don't that we don't tend to prove
Theory's correct we usually do
experiments that either disprove the
theory or support the theory but there's
no proving the theory we also have a
concept called a law in science a law is
a concise scientific statement of fact
it's frequently mathematical in nature
so we have the law of mass energy
equivalence which you know of is
Einstein's theory of relativity equals
MC squared as part of that we have
dalton's law of partial pressures which
is which is a law that you will learn in
the gas section in unit 6 and we have
Newton's second law which is one of the
fundamental basis of modern physics this
is a law that states that force is equal
to the mass of an object times its
acceleration matter is defined as
anything that has mass and a volume or
anything that has mass and takes up
space so what is mass mass is a measure
of how much matter you actually have for
example if we have a human on earth that
has a certain amount of mass say they
they have a mass of 70 kilograms if you
took them to the moon their weight would
be very different but their mass would
remain exactly the same because they
have the same amount of stuff of matter
in that object in their body whether
they're on earth or whether they're on
the moon and chemistry is the study of
matter how it undergoes changes and the
energy that accompanies these changes in
most chemical reactions either energy is
produced by that reaction or energy is
actually absorbed by that reaction and
you can tell the difference very easily
if the reaction gets hot its producing
energy if it feels cold it feels cold
because it's absorbing heat from its
surroundings and that would be a
reaction that absorbs he-he energy
during its process so the scientific
method
is a is a multi-step pathway and this is
just the general pathway it can be done
in practice in a number of different
ways but this is one way to look at it
we start with observations you notice
something about the world around you
about the nature around you and once you
notice these things you begin to ask
questions how does this work
what makes this go why does this do this
and that will lead you to make a guess
about why these things work your guests
may be right your guests may be wrong
and may be completely wrong it may be
only a little bit wrong but it has to be
a testable guess and we call these my
hypothesis or hypotheses for plural so
it must be testable why is it testable
well if you come up with a hypothesis
that says a magic creature in the sky
has made this disappear and that's why
it disappears or or a magical elf moves
this water from here to here and that's
the reason well that's not particularly
testable we can't make a test that
proves or disproves that as so or at
least we can't make a test that
disproves it or supports it so you have
to make a hypothesis a guess that can be
tested and once you make that guess that
can be tested hey I think that this is
due to natural forces that are pulling
this rock towards the earth or I believe
that wind pressure air pressure is
pushing this object from here to here
those are hypotheses that are testable
and then you design a test the tests the
hypothesis what when you have to ask
yourself what would prove my hypothesis
wrong what result would I get that would
say my hypothesis was wrong so then you
do you experiment you look at your
results and you ask yourself does the
result disprove my hypothesis or does it
support it we don't tend to say that it
proves it because you can't really prove
a hypothesis you can't really prove a
theory you can only disprove it or
support it and once you do the
experiment you decide whether it
disproves or supports it we do further
analysis and we ask the question does
the hypothesis need to be modified
is it good the way it is do we need to
tweak it a little bit or is it
completely wrong and we have to start
all over again well if it's completely
wrong we have to start all over again we
look back at observations and we go
through the same cycle again and if if
it has been tested and so that each test
supports our hypothesis we then call
that a theory or a scientific theory so
the way we use the word theory in
science is very different than the way
we use theory in everyday English theory
and science means this is an idea about
how something works that has been tested
so many times in so many ways and it's
been never it's never been disproven and
that is what we call a theory so we have
a lot of theories in science that are
considered the true explanation until
somebody comes up with a better one
things like natural selection is a
mechanism for for evolution or cell
theory worse also known as cellular
theory for a mechanism about how cells
work in organisms living organisms
