a.
b.
c.
d.
Review Questions
1. Classify the following statements as an example of an experiment, hypothesis, theory or law.
The ashes from a campfire weigh less than the wood that was burned. Therefore mass is destroyed
(or lost) when wood is burned
(hypothesis)
A body at rest tends to stay at rest, while a body in motion tends to stay in motion.
(law)
Water boils at 100 °C on your kitchen stove and in the laboratory. (experiment)
All matter is composed of atoms, which themselves are composed of protons, electrons and
neutrons.
(theory)
2. Define Chemistry.
CHEMISTRY - the branch of science that deals with the composition, structure and properties of
matter, with the changes that matter undergoes in composition and with the energy changes that
occur during these transformations (changes).
3. Explain theory, hypothesis and law.
Theory – the hypothesis can become a theory, which is a thoroughly tested model that explains why
things behave a certain way. A theory – explains why the system behaves that way. The Kinetic
molecular model explains gas behaviour in terms of molecules moving.
A theory can never be proven but is useful because the theory can be used to predict behaviour and
help us form mental pictures of processes (models).
Hypothesis - observations lead to an educated guess as to the cause of the problem or answer to a
question (Hypothesis). Experiments are designed to test the hypothesis and generate more data
(observations).
Law - certain behaviour is repeated many times. The results are predictable so a scientific law is
developed. The laws are a description. Scientific law – predicts how a system behaves Gas laws explain
how the volume of a gas changes when the temperature or pressure is changed.
4. What is the purpose of an experiment?
Experiments are designed to test the hypothesis and generate more data (observations). Experiments
are activities carried out under controlled conditions in which there are two variables: the
experimenter manipulates one the conditions - the independent (manipulated) variable to see the
effect that this change has on another condition - the dependent (responding) variable.
5. Classify the following statements about carbon as observations or interpretations (inferences).
a)
Carbon burns slowly with a yellow flame.
observations
b)
Carbon burns faster when placed in oxygen.
observations
c)
Carbon atoms react with oxygen molecules from the air to produce molecules of carbon
dioxide and carbon monoxide. inferences
6. Classify the following statements as qualitative or quantitative.
a) The candle flame was about 4 cm high.
quantitative
b) Carbon is a black solid at SATP (room temperature 25ºC and pressure 101.3kPa).
qualitative
c) Coal is our primary source of carbon.
qualitative
7. Classify the following statements as empirical or theoretical knowledge
a) Most carbon atoms consist of 6 protons, 6 neutrons and 6 electrons.
theoretical
b) There are several forms of carbon in nature: lampblack, charcoal, graphite and diamond.
empirical
c) Graphite conducts an electric current; diamond does not conduct an electric current.
empirical
d) Graphite contains loosely held electrons; diamond contains electrons that held tightly held.
theoretical
8. Use the Kinetic Molecular Theory (Model) to explain the properties of the three states of matter;
solid, liquid and gas.
Particles in solids have very strong intermolecular forces (attractive forces between the
particles), which hold the particles in place – think of tiny magnets attracting. These strong
forces lead to vibratory motion in solids, ↔ the particles are very limited in motion. Therefore,
solids have definite volume and shape.
In liquids the intermolecular forces are weaker and allow particles to slide by one another –
think of marbles being poured. The forces are strong enough that the particles cannot escape
from the other particles. There is a greater degree of freedom of movement – liquids do not
have definite shape but have definite volume.
Gases consist of small particles that are far apart in comparison to their own size. There are no
attractive forces between gas particles or between particles and the sides of the container with
which they collide. Gases will expand to fill their container. Because of the great degree of
freedom gases do not have definite shape or volume.
9. A biologist took two identical plants. She placed one of the plants into a glass enclosure. The
other plant was placed in a solid box not exposed to light. Both plants were exposed to constant
humidity, temperature and no water for four days. The plants were weighed before the
experiment began and again after four days.
Identify
a) the manipulated variable
Light
b) the responding variable
growth or weight of plant
c) the controlled variables
Two identical plants, constant humidity, temperature and no water for four days
10. What is the state of each of the following at SATP?
a.
silver
SOLID
b.
gasoline
LIQUID
c.
d.
e.
helium
GAS
paraffin wax
SOLID
rubbing alcohol
LIQUID
11. Classify the following as heterogeneous or homogeneous mixtures.
a. blood
heterogeneous
b. chocolate-chip ice cream
heterogeneous
c. brass
homogeneous
d. milk
heterogeneous
e. cup of coffee
homogeneous
12.
A clear liquid in an open container is allowed to evaporate. After three days a solid residue is
left in the container.
Was the original liquid an element, compound or mixture?
Explain how you arrived at your answer.
clear liquid – homogeneous: either mixture or pure substance. Residue after evaporation must
be a mixture.
13. Classify the following as an element, compound or mixture:
a. argon
element
b.ethanol (C2H5OH)
compound
b. grape juice
mixture
c. blue cheese
mixture
d. zinc
element
14. Classify the following changes as physical or chemical:
a.
food spoils
chemical
b.
water boils
physical
c.
a nail rusts
chemical
d.
bread bakes
chemical
e.
sugar dissolves in water
physical
f.
a snowflake melts
physical
15. List four physical properties of a common nail.
Solid, gray, pointed end, flat head cylindrical shape
16. Match each state with the terms on the left. More than one state can match each term.
a.
incompressible
liquid, solid
b.
indefinite shape
gas, liquid
c.
definite volume
liquid, solid
d.
flows
liquid, gas
17. (a) What is the difference between a heterogeneous and a homogeneous mixture?
Heterogeneous is not uniform in composition. Example: salt and pepper mixed together; there are two
phases visible – solid salt and solid pepper.
Heterogeneous mixtures – at least two phases present.
Homogeneous is completely uniform composition. Example: a salt solution only one phase visible.
A solution is a homogeneous mixture. A solution contains a solvent that is the dispersing medium and a
solute that is the substance that is dissolving.
(b) How can the components of a mixture be separated?
Separated by physical means.
18. What are two ways to distinguish between an element and a compound?
Element – one kind of atom present; can not be broken down into simpler substances
Compound – more than one kind of atom present, can be broken down into simpler pure
substance.
19. Classify the following as a physical or chemical change:
a.
bending a copper wire
physical
b.
burning propane
chemical
c.
cooking hamburger
chemical
d.
cutting the grass
physical
20.
Describe how to distinguish between each of the following pairs.
a) Heterogeneous matter at least two components that maintain their own properties.
Homogenous matter one phase of matter can be a mixture or a pure substance.
b) solutions –
homogeneous mixture (2 substances 1 phase)
pure substances –
one kind of matter present (1 phase)