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Class Notes - Unit 1: Chemistry, Matter, and Change
Ch. 1 pg. 7-23 and Ch. 2 pg. 39-55
Chemistry is the study of matter. More precisely it is the study of the properties of matter
and the changes that matter undergoes. These two major concepts (properties/types of
matter and changes) are the focus of this first unit.
Matter is anything that 1) takes up space (volume) and 2) has mass.
Remember that there is a difference between mass and weight. Mass is the amount of
“stuff”- the amount of matter in an object. Weight is the effect of gravity on that amount.
Your weight changes when you go between the Earth and the moon because the amount
of gravity changes. However, the mass of you on Earth and on the moon is exactly the
same because you still have the same overall amount of matter.
There aren’t many things that aren’t matter. Even things that you don’t normally think of
as being matter actually are. For example, air is matter. It takes up a certain amount of
space (volume) and it also has mass (it is made up of carbon dioxide, oxygen, and
nitrogen - all things that have mass to them).
Chemistry is a subject that studies many facets of the world around us and almost
everyone studies chemistry in high school. It is such an important topic to learn because it
affects your daily life in so many ways and when you know and understand chemistry
you have the ability to control and create many things.
There will be a lot of experimentation done throughout this course. Throughout all of our
labs it is good to make good detailed observations (recording the facts of what you see)
and then use what we learn in this class as well as prior knowledge to infer and draw
conclusions as to why what you saw happened. Be careful not to let your inferences cloud
your observations. If what you expect to happen for some reason didn’t sometimes that
can be just as meaningful; it is important to try and find out and explain why you got
different results.
Lab Techniques
Safety is of paramount importance and should always be in mind in the lab. You should
know where the shower, eyewash station, phone, fire blanket, fire extinguisher, and gas
shut offs are located in the lab and how/when to use each of them. Remember when a
person is on fire, the fire blanket should be used over the fire extinguisher.
Another thing to consider in lab is the type of equipment you are using to complete your
experiment as well as the size/accuracy of that equipment. To get the mass of a sample,
you should use a balance. Zeroing or taring the balance before use will ensure that it is
calibrated for you to use. You should not mass chemicals directly on the balance; you
should use either weigh paper or glassware. Whatever secondary thing you are using to
contain the chemical you are massing (paper or glassware) can be discounted from the
overall mass by again pressing the zero or tare button after it has been put on the balance.
This is a good habit to form so that you are actually getting numbers of the chemical you
are interested in and do not have to remember to subtract out the mass of the paper or
glassware.
To find the volume of liquids, beakers or graduated cylinders are most typically used.
You need to take into consideration the amount and the accuracy of the sample you want
to get the volume of. If you only need an approximate amount, a beaker can be used;
however, if you need a more specific amount, a graduated cylinder should be used
(particularly one close to the size range of what you are measuring). To transfer small
amounts of liquid or to more precisely fill a graduated cylinder, a pipet can be used. The
plastic disposable pipets hold about 1 mL of liquid.
General equipment to transfer chemicals includes spatulas and tweezers for solids and
pipettes for liquids. When putting something into a small opening, such as a graduated
cylinder or a test tube, you should use a funnel to minimize spills. Use a powder funnel
(plastic with a larger opening on the bottom) for solids and a filter funnel (glass) for
liquids.
To heat things, a Bunsen burner or hot plate can be used. To use a Bunsen burner, be sure
that the tubing is snuggly fit on the valve. Make sure you have a lighter that gives you a
good, reliable spark. Turn the valve all the way open so that you can hear the gas flowing.
Hold the lighter spark side down about an inch over the top of the burner and create a
spark. After your flame is lit you can adjust the height of it by adjusting the valve. Most
things heated by a Bunsen burner should be suspended over it using a ring stand and the
appropriate clamps (ring or test tube). Some things can also be heated by placing them
directly on a hotplate. Most of our hotplates also have magnets in them that will stir
things placed on top if you add another magnet to what you want stirred. You will be told
when to use a burner or a hot plate.
In general, you should NEVER put chemicals back into their storage containers for risk
of contaminating the entire container. Experiments should be carried out on the higher
portion of you lab benches and you should stand during experimentation with your stools
pushed in. Unless I tell you otherwise, the chemicals we use in lab are safe to put down
the sink as long as you put them down with water. All equipment and benches should be
cleaned at the end of every lab. This includes rinsing all glassware with water and
hanging them above the sink to dry.
Physical and Chemical Properties
What’s the best way to describe matter? If you wanted to describe what a penny was,
what type of terms would you use? You would describe its properties. Different forms of
matter have different properties and it’s those properties that distinguish them.
Activity: Describe the properties of your treat.
Most properties listed are physical. If you were instead describing a person, would you
only describe their size, shape, state of matter, flexibility, etc? No. You would talk about
their personalities as well (whether they were kind, etc). Just like people, matter has
“personalities” as well. These are known as chemical properties.
Physical properties
- characteristics of matter that can be observed without changing the object into
another type of matter.
- Ex: Size, weight, shape, texture, color, flexibility, odor, density, solubility
(whether it can dissolve), magnetic, state of matter (whether it is a solid, liquid, or
gas), boiling point, melting point
Chemical properties
- properties that can’t be observed without changing the object into a new
substance, a new type of matter
- each chemical property describes the matters ability in some way to transform
into a new type of matter
- Ex: flammability (ability to burn), reactivity (ability to react)
No two substances have identical physical and chemical properties. It is the unique set of
properties that something has that allows us to distinguish one thing from another.
Why is boiling a physical property and not a chemical property? When something boils,
it changes its state of matter from a liquid to a gas. It does not change the type of matter
that it is. For example, when water boils it changes from liquid water to water vapor but it
is still water. For the property to be a chemical property the type of matter has to change.
For example, when an iron nail rusts the iron in the nail reacts with the oxygen in the air
to form a new substance (the rust, also known as iron oxide). The iron nail therefore has
the chemical property of reactivity.
Physical Changes
A physical change is any change that alters the form or appearance of matter but does not
make the matter into a different substance. In a physical change, the substance (the type
of matter) is the same before and after the change.
There are two common types of physical changes: a change of state and a change of
shape. A change of state is a physical change where the state of matter of the substance is
changed. The state of matter is whether it is a solid, a liquid, or a gas. This type of change
is reversible. For example, if you have a cup of water and you freeze it, it has just
changed its state of matter from liquid to solid – it is still water (the same type of matter).
When you do the opposite and melt the frozen ice you get the exact same cup of water
back that you started with. This change is completely reversible.
A change of shape is usually an irreversible change. For example, if you crush an
aluminum can you have changed its overall appearance but not the type of matter it is
(it’s still just and aluminum can). This type of change is usually irreversible because it is
very difficult to get it back into the exact original shape. These types of physical changes
are definitely irreversible if it involves cutting or breaking the matter. For example, if you
tear a piece of paper, there is no way for it to go back together naturally.
Chemical Changes
A chemical change is also known as a chemical reaction. A chemical change/reaction is
any change that transforms one substance into another substance. It always produces new
substances with properties different from the original substances. Chemical changes can
also be reversible or irreversible.
There are four indicators that a chemical change has occurred:
1) Formation of a solid precipitate upon mixing two solutions.
2) Production of gas bubbles (not due to a physical change such as boiling)
3) Color change (not due to dilution or color mixing)
4) Temperature change (not due to external heating or cooling)
It is possible for chemical changes to occur without one of these four indicators being
present, however most common chemical changes exhibit at least one of these four.
Chemical reactions are represented by chemical equations. A chemical equation is a
quick, shorthand notation used to convey as much as possible about what happens in a
chemical reaction. Reactants are the general name given to all the elements or compounds
that you have before the chemical change has taken place. Products are the general name
given for all elements or compounds that you have after the change has occurred.
Reactants are shown on the left side of the equation and products are shown on the right
side. The reactants and products are separated by an →. This arrow is can be interpreted
as “yields”, “produces”, or other words describing the type of chemical change.
Reactants → Products
If there are more than one reactants or products, they are separated by a + sign. For
example, in the reaction between iron and oxygen to produce rust (Fe2O3) the chemical
equation is:
Fe(s) + O2 (g) → Fe2O3 (s)
Another useful piece of information contained in chemical equations can be the states of
matter that the reactants and products are in. The four options are: (s) for solid, (l) for
liquid, (g) for gas, or (aq) for an aqueous solution (a solid dissolved in water to make a
homogeneous mixture).
Ex: NaCl(s) = solid table salt
NaCl(aq) = a solution of salt water
Every chemical reaction obeys the Law of Conservation of Mass (aka the Law of
Conservation of Matter). This states that matter is neither created nor destroyed. What
this means to us is that whatever mass you start out with is the same amount of mass you
end up with. For example, in the above equation if you start with 5 g of Fe and end up
producing 6.2 g of Fe2O3 you will have reacted your iron with 1.2 g of O2. Your reactants
started with a total of 6.2 g of mass (5+1.2) and your product totaled 6.2 g of mass. The
matter was rearranged however the total mass was still the same. Matter/mass is never
created or destroyed - it is only rearranged.
States of Matter
The three states of matter are solid, liquid, and gas. The way that you convert from one
state to another is by increasing or decreasing temperature. Temperature is a measure of
the amount of heat energy something has. If something has a high temperature is has a lot
of energy and the particles move faster and tend to spread out. If something has a low
temperature is has a very low energy and the particles move slowly and are often closer
together. The state of matter that something is at room temperature all depends on the
inherent strength of the forces between the particles in the substance. If the particles have
very strong forces between them, the substance will most likely be a solid. If the particles
have very weak forces between them, the substance will most likely be a gas.
If you look at the particles of a solid, they are very tightly packed in a rigid arrangement.
They still have some slight vibrations between the particles however as a whole they have
very little movement. They are low energy. Solids have a definite shape and volume
because of the tightly packed nature of their particles. The particles in a solid can either
be very orderly arranged (to make a crystalline solid) or not arranged in any specific
order (to make an amorphous solid).
If you look at the particles of a liquid, they are in close contact but not rigidly packed.
They have enough space between their particles that they can slide past each other. This
is what allows a liquid to flow. Liquids have more energy than solids and it is this energy
that makes them be more spread out and faster moving. Liquids have no definite shape
and take the shape of whatever container they are in; they do however, have a definite
volume and aren’t easily compressed or expanded.
If you look at the particles of a gas, they are very far apart and very fast and free moving.
Gas particles have a lot of energy (gotten from the temperature increase that is needed to
make things in the gas state). Gases have an undefined shape and volume and tend to
expand or contract to fill whatever they need to. On a technical note, the term “gas” refers
to something that exists in a gaseous state at room temperature (like oxygen, carbon
dioxide, etc). For things that are liquids or solids at room temperature, when they are in
the gaseous state, they are called “vapor.” For example, water in a gaseous state is
referred to as water vapor not water gas.
Each of the three states of matter can also be described by the amount of entropy, or
disorder, they have in them. In a gas, the particles have a lot of disorder and therefore
very high entropy. In a solid, the particles are closely packed together with much more
order; therefore they have low entropy.
Matter does not change it’s state until all the particles in the sample have gained or lost
enough energy to change to another state. This idea is shown in the flat parts of the
heating curve (plotting temperature vs. time).
Classifications of Matter
The properties of matter and the changes that matter undergoes (ie: chemistry) depends
on the makeup of the matter. Matter can either be a substance or a mixture.
Substances: Elements and Compounds
A substance is a single type of mater; matter with a single composition and set of
properties. For example: aluminum foil, water, and salt are all substances. No matter
where you get your aluminum foil from it is always the same single type of matter –
aluminum.
Substances can be further classified as either elements or compounds. An element is a
pure substance that cannot be broken down into any other substance. Elements are the
simplest substances. In your life you see elements all the time (aluminum in aluminum
foil, tin in tin cans, the air is nitrogen and oxygen gases. There are over 100 elements
currently discovered. All elements are found on the periodic table represented by one or
two letter symbols. If it is not on the periodic table, it is not an element. Each element has
its own physical and chemical properties. For example, aluminum has very different
properties than oxygen.
If you take an element and cut it in half and continue cutting it in half until you can’t
anymore and have it still have the same properties of that element, then you have an
atoms. For example, if you take a solid copper penny and you keep cutting it in half until
if you cut it in half once more and it no longer has the properties of copper, then that last
size that you have before you lose its properties is an atom. In a solid copper penny, there
are approximately 1,000,000 copper atoms. Atoms of different elements have the ability
to join. Chemical bonds are the attractive force between two atoms that holds them
together.
Compounds are pure substances made up of two or more atoms chemically combined in a
set ratio. Compounds are represented by a chemical formula (Ex: H2O, CO2). Because a
compound has a fixed composition, the formula for a compound is always the same. The
subscript in the formula tells the numbers of each atom involved. For example, water
(H2O) is two hydrogen atoms combined with one oxygen atom. During chemical
bonding, the properties of the substances involved changes. Compounds have properties
very separate and distinct from the elements they are made up of. For example, sugar
(C11H22O11) is a compound that can be broken down into carbon (ash) and water (H2O).
Each of those simpler substances that it is broken down into has very different properties
from those of sugar.
Sugar Snake: www.metacafe.com/watch/403829/inappropriate_chemistry/
What is the same about elements and compounds? They are both substances; meaning
that they both have a fixed, uniform and definite composition.
What is the difference between elements and compounds? Whether or not they can be
broken down into simpler substances.
Can compounds be broken down into simpler substances? Yes.
Can elements be broken down into simpler substances? No.
Compounds are two or more elements chemically combined (chemically bonded) through
chemical reactions and they are broken down into their element components through
chemical reactions.
What is the ratio of atoms in CO2? There is one carbon atom combined with 2 oxygen
atoms. Is CO2 the same as CO? No. CO2 carbon dioxide is the compound we breathe out
when we exhale. CO, carbon monoxide, is a deadly gas. That tiny difference of one
oxygen atom in the compound makes a big difference in terms of the compound’s
properties.
Is water an element? What about wood? None of these are elements. They are very
commonly used substances, but not elements (not single types of atoms). All elements are
listed on the periodic table. Water and wood are compounds, they are different atoms put
together in a set ratio. They can all be broken down into elements. For example, water is
a compounds and can be broken down into the elements hydrogen (H) and oxygen (O).
Salt (NaCl) is a compound and can be broken down into the elements sodium (Na) and
chlorine (Cl).
Mixtures
Most things you encounter, however, aren’t usually a single substance (not just an
element or a compound). They are mixtures. Mixtures are two or more substances that are
in the same place physically but not chemically combined (not chemically bonded). Each
substance has and retains its own set of properties.
Is soda a mixture? Yes, there’s water, caffeine, color, flavor, preservatives, etc. Is chicken
noodle soup a mixture? Yes, there’s broth, chicken, noodles, vegetables, etc. Is there a
difference between these 2 mixtures? Mixtures have variable compositions and when
describing a mixture, how the components of a mixture are distributed can be an
important piece of information. In the soup, there are distinct parts of the mixture. It is
not evenly mixed. One bite you may get a vegetable while another bite you may get a
noodle. Any mixture where the composition is not uniform (the components are not
evenly mixed together) is known as a heterogeneous mixture. The distinct parts of a
heterogeneous mixture are known as phases. A mixture where the composition is uniform
is known as a homogeneous mixture. Homogeneous mixtures are also known as
solutions. Many solutions we commonly think of are liquid mixtures, however you can
also have solutions of gases (ex: air is a homogeneous mixture of nitrogen, oxygen, and
carbon dioxide) and solids (ex: stainless steel is a homogeneous mixture of iron,
chromium, and nickel).
Deciding whether something is a substance or a homogeneous mixture can sometimes be
hard. They both appear to only have one type of matter. A good way to determine if
something is a mixture is to think if it is possible to have different version of it (different
compositions of it). For example, milk is a mixture of many things and we know this
because you can get different versions of it (whole, 2%, 1%, skim) where they change the
ratios of the components of this mixture. But generally, they are all still classified as
“milk.”
Separating Mixtures
Compounds are held together with chemical bonds and separated into elements based on
chemical properties. Mixtures are in the same place physical and are separated into their
components based on physical properties. You need to undergo a chemical reaction (a
chemical change) to separate compounds into their smaller parts. You only need to
physically separate the components of mixtures.
The easiest way to separate a mixture is to look at the physical properties of the things
involved in the mixture and see if there is one property that is specialized to one part of
the mixture that would make it easy to pull out. For example, if you have a mixture of
sand, salt, and iron. The iron has the physical property of being magnetic where the sand
and salt do not; so running a magnet over the mixture would easily separate out only the
iron.
To separate mixtures, many physical properties can be used to sort manually or using a
specialized machine. These include separating things based on color and texture. In other
instances, filters are a tool used to separate mixtures. One of the most common uses of
filtration is to separate a solid from a liquid (so the separation is based on the physical
property of state of matter). Filters can also be used to separate mixtures based on size,
shape, and flexibility. Another common way to separate liquids from a mixture with
solids is evaporation. If some of the components of the mixture are magnetic, a magnet
can be used to separate a mixture.
Solubility, or the ability to dissolve, is also a common physical property used to separate
mixtures. It is often combined with another method to fully separate. For example, if you
wanted to separate salt from sand. You could add water to dissolve the salt since a
physical property of salt is that it is soluble in water. Then the mixture could be filtered,
collecting the sand and letting the salt water pass through. Then the salt water could be
allowed to evaporate, leaving only the salt behind.
Boiling points are also used to separate mixtures. This is particularly useful when trying
to separate a mixture of liquids. This process of separating liquids based on their boiling
points is known as distillation. In distillation, the mixture of liquids is heated. Once the
temperature of the mixture is equal to the boiling point of one of its components, that
component will boil and change into a gas. The gas will travel upwards. A cold tube is
put in place to collect the gas. When the warm gas hits the cold tube, it condenses and the
pure liquid can be collected. Finally, a common physical property used to separate
components of a mixture is density.