KD McMahon
Reseda Science Magnet
Introduction to Chemistry
Summary:
Most of the phenomena that occur in the world around us involve chemical
changes. Chemists try to understand these changes and harness them to the betterment of
society. To this end chemists employ rigorous methodologies. Students may find the
study of chemistry challenging, but with persistent effort they can be successful.
Objectives:
* Define chemistry and discuss the methodologies used by chemists to study matter and
its changes.
* Employ the scientific method in laboratory experiences.
* Discuss and employ proper laboratory techniques.
* Describe matter, its properties, and states.
* Classify matter according to type.
* Describe physical and chemical changes of matter.
What is Chemistry?
Chemistry is the study of the composition, structure,
and properties of matter, the changes that matter undergoes,
and the energy accompanying these changes. Chemists
employ rigorous methodologies (ie: the Scientific Method)
in their study of matter. Chemists follow prescribed
laboratory techniques to improve the precision of their
experimental results and to assure safety.
Question #1: Classify the following statements as
observation, hypothesis, experimentation, etc.
a.) Measure the boiling point of water after the addition
of a solute.
b.) Matter is neither created nor destroyed in chemical reactions.
c.) A base solution turns pink with the addition of phenolphthalein.
d.) Schrodinger proposed that the exact location of an electron in an atom could not
be known with certainty, only the probability of its location could be known.
Questions #2: What is wrong with the following statement, “The results of the
experiment do not agree with the theory. Something must be wrong with the
experiment.”
What is Matter?
Everything in the universe is made of matter. Matter is anything that takes up
space (ie: has volume) and has mass. Matter can be described "qualitatively" and
"quantitatively." A qualitative property is one that we ascertain with our senses and is
expressed with words. A quantitative property expresses a property with numbers.
Scientific instruments are used to measure the quantitative properties of matter.
Matter can also be described as having physical and chemical properties. Physical
properties include characteristics of matter such as its mass, volume, density, color, odor,
texture, hardness, melting and boiling points, solubility, conductivity, etc. The chemical
properties of matter describe the tendency of matter to react with other types of matter
under various conditions.
Question #3: Classify the following as either a qualitative or quantitative property and
either a physical or chemical property.
a.) Water becomes a liquid when melted.
b.) Water becomes a gas when at 100°C.
c.) At the equivalency point just enough NaOH had been added to HCl to turn the
solution pink.
d.) At the equivalency point just enough NaOH had been added to HCl to cause the
solution to have a pH of 7.0.
The Kinetic Theory states that all matter is in motion. Even when matter is held in place
in a solid the tiny particles are vibrating. [It is believed that the motion of matter does
stop at the theoretical temperature of -273 K]. Matter can exist in one of three phases or
states depending on the kinetic energy of its particles.
In the solid phase, the kinetic energy of the
particles are limited to the motion of vibration. The
particles are held tightly together in a lattice structure.
Consequently, solids have definite shapes and volume.
In the liquid phase, the motion of the particles is greater.
The particles' energy is great enough to break the
attractive forces of the lattice structure. The particles of
the liquid still attract each other, but the particles are
free to move around. Consequently, liquids do not have
definite shapes, but they do have definite volumes.
In the gas phase, the energy of the particles is so great
that they overcome all attractive forces. Consequently,
gases do not have either definite shapes or volumes;
they conform to the shape and volume of their container.
Question #4: Classify the following as solid, liquid, or gas.
a.) definite volume; indefinite shape
b.) indefinite volume; indefinite shape
c.) definite volume; definite shape
Question #5: One of the defining properties of matter is density which is defined by
the equation: Density (D) = mass (grams)
Volume (cm3)
a.) A rectangular block has dimensions 2.9 cm X 3.5 cm X 10.0 cm. The mass of the
block is 615.0g. What are the volume and density of the block?
b.) A sample containing 33.42 grams of metal pellets is poured into a graduated
cylinder initially containing 12.7 mL of water, causing the water level in the
cylinder to rise to 21.6 mL. Calculate the density of the metal.
c.) The density of pure silver is 10.5 g/cm3 at 20°C. If 5.25 g of pure silver pellets is
added to a graduated cylinder containing 11.2 mL of water, to what volume level
will the water in the cylinder rise?
Types of Matter:
Matter is classified as either a pure substance or an impure mixture. A pure substance has
the same composition throughout. A mixture is a physical blend of two or more
substances.
Pure substances are composed of either elements or compounds. Elements are the
simplest forms of matter that can exist under normal laboratory conditions. These
substances are the building blocks of all matter. Compounds are composed of two or
more elements. They can be separated into simpler substances only through chemical
processes.
Heterogenous mixtures are not uniform in their composition. Homogenous
mixtures are uniform throughout their composition. Solutions are examples of
homogenous mixtures. Some examples of solutions include: Liquids in Liquids (wine),
Solids in Liquids (sea water), Gases in Liquids (carbonated soda), Solids in Solids (14K
gold ring), Gases in Gases (air).
Solutions are composed on a solute and a solvent. The
solvent is the dissolving medium of the solution. The
solute is the dissolved particles in the solution.
Solutions do not "settle out" nor will it "scatter" light.
Mixtures can be separated into their constituents
through physical processes. Solutions can be separated
by a process known as distillation.
Question #7: Classify the following as either an element, compound, heterogenous
mixture, or a homogenous mixture (solution):
a.) soil
b.) the atmosphere
c.) carbonate soft drink (unopened)
d.) carbonated soft drink (opened) e.) gasoline f.) gold
g.) blood
h.) water
i.) brass
j.) table salt (NaCl) k.) water + ethanol
Question #8:
a.) Pick one of the above (from #7) and describe how you might separate them using
a physical technique.
b.) Pick one of the above (from #7) and describe how you might separate them using
a chemical technique.
Matter Changes:
During a physical change a substance is altered
without changing its composition. Changes of state
are physical changes. Changes of state or phase
(solid --> liquid --> gas) are also physical changes.
In a chemical reaction, one or more substances
change into new substances. The substances that
undergo the changes are known as reactants. The new
substances formed are called the products. The word and
paper undergo a chemical change upon combustion as
cellulose is converted to carbon dioxide and water vapor.
Chemical reactions are written in shorthand notation:
A + B ---> C + D where A and B are the reactants and C and D are the products. During
chemical reactions energy is either released or absorbed.
Photosynthesis is the reaction in which green plants combine water and carbon dioxide to
produce glucose. This reaction absorbs the energy of sunlight.
6H2O + 6CO2 ---> C6H1206 + 6O2
The chemical reactions of cellular respiration (the reverse of the above reaction) involve
the breakdown of glucose to water and carbon dioxide. During these reactions energy is
released to the cell.
During physical and chemical changes matter is neither created nor destroyed; it is
"conserved." This is known as the Law of Conservation of Mass. During every chemical
reaction the mass of the products equals the mass of the reactants.
Mass is not conserved during nuclear reactions because some mass is converted into
energy. When a high-energy neutron collides with a uranium atom nuclear fission occurs.
This results in the formation of two new elements, barium and krypton. Gamma rays and
beta particles are released and a small amount of matter is converted into energy.
Question #9: Classify the following as a physical, chemical, or nuclear change.
a.) Moth balls gradually sublimating in a closet.
b.) Hydrofluoric acid attacks glass, and is used to etch calibration marks on glass
laboratory utensils.
c.) A French chef making a sauce with brandy is able to burn off the alcohol from the
brandy, leaving just the brandy flavoring.
d.) Hydrogen atoms fuse to form Helium in the core of the Sun.
e.) Spilling bleach on a pair of jeans and turning them white.