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Celia Perez
PS- 4th
Dec. 16, 2010
1. How do you know that the air you breath is matter, even though you can’t see it?
ANS: Possible answer: Matter has weight and takes up space. You know that air takes up
space, because when you breathe in , your lungs fill with air and expand.
2. Explain the difference between the following three substances: carbon (C), carbon dioxide
(CO2), and oxygen(O2).
ANS: Carbon represents a pure element. Carbon dioxide is a molecule formed by chemical
combination of carbon and oxygen. It is unlike either carbon or oxygen Oxygen is a molecule
made up of two like atoms.
3. “ Carbonated drinks are homogeneous mixtures.” Explain this statement.
ANS: Carbonated drinks are mixtures of water, sugar, flavorings,and dissolved carbon gas.
They are homogeneous because the mixing occurs between the individual units and is the
same throughout.
4. You go into a coffee house, and the whole place is filled with the pungent smell. Explain what
is happening, according to the kinetic theory.
ANS: As a substance is heated, the molecules it is made of move faster and faster. Eventually,
some escape in the form of gases, and it is those molecules that reach your nose and cause the
rich smell.
5. Explain what it means to state that energy is transferred in order or any change of state to
occur. Give at least two examples.
ANS: Any change of state involves either heating or cooling, which is energy transfer between
substances. When water freezes, it releases energy into the surrounding air. When ice melts, it
absorbs heat energy.
6. Describe the chemical and physical properties of the case that protects your computer.
Explain why the materials used were chosen.
ANS: Hard plastic: hard solid at room temperature, nonreactive, smooth, dull in color. Hard and
solid to protect the computer; nonreactive to be durable ;smooth to be easy to clean; dull in
color to blending with surroundings.
7. Why is density an important property of matter? Explain at least two ways in which density
has practical importance.
ANS Density affects how heavy something is, as well as whether something floats in a particular
liquid. Boats float because the air inside the vessel is less dense then the water the vessel sits
in. Cream can be separated from milk because it is less dense than milk and floats to the top.
8. Explain what it means to say that a chemical change is a change composition. Give an
example of a chemical change and state what changes occur.
ANS: In a chemical change, substances react together to produce new substances. For
example, rusting of iron is a chemical change. Oxygen in the air reacts with the iron to produce
iron oxide, a new substance that is neither iron nor oxygen.