0001-07-selftest-ans

Online Introductory Chemistry

Practice self test. Answer any 4 questions. All questions have equal weight. Allow 20 minutes.

1.

What are the three states of matter? Which one is the most organized? What is the state of matter depicted in the flask below? Sketch a picture of the least compact state showing 11 atoms in the same size container.

Answer: Solid, liquid, and gas are the commonly identified states of matter. The solid state is the most organized.

This drawing shows 11 atoms in the liquid state. The atoms are close together, but there is no regular pattern.

The gas state has the 11 atoms randomly scattered around the interior of the flask. On average they would be far apart. The gas particles will collide with one another but they don't stick.

2.

Give the symbols for the following elements. Tell which is a metal and which is a nonmetal. Why do some of the names have no relation to the English name for the element? Answer:

symbol

class (metal or nonmetal)

carbon

C

nonmetal

calcium

Ca

metal

potassium

K

metal

sodium

Na

metal

The elements like sodium and potassium have names dating back to the Romans. The symbols are taken from the old Roman names.

3.

Tell how a combination of sand, salt and iron filings can be separated.

Answer:

A magnet can be used to "draw" out the iron filings. Water can be used to dissolve the salt away from the sand-salt residue. The wet sand can be dried. The salt water mixture can be separated by boiling off the water. The residue will be the salt, sodium chloride. Evaporation of the water will also work with the same result.

4.

Explain why energy is not destroyed when a match is used to light a candle. What happens to the energy released in the flame?

Answer: The energy is not destroyed it is transferred from the match to the wick on the candle. The cold wick is heated enough so it can ignite. The location and concentration of energy changes.

5.

Why are there subscripts on the symbols for atoms in a chemical formula? What is the importance of the subscript 3 on the carbon atom in propane, C₃H₆?

Answer: The subscripts tell the count for each type of atom in the formula unit. Changes in the subscripts result in a different formula and a different compound. The three indicates the number of carbon atoms in a formula unit of propane. Every propane molecule has to have exactly three carbon atoms.

6.

A pendulum is a common device. When the weight at the end of the pendulum is at the bottom of its swing it is moving faster than at any other point. What is the point in the swing when the weight is not moving at all? Which position matches the lowest kinetic energy and which is the highest?

Answer: The pendulum weight is travelling slowest when it reaches the top of its swing. In fact the weight comes to a stop at the top of its swing. Try this with a yoyo or any object attached to a string. The top of the arc or swing matches the lowest kinetic energy. The bottom of the swing is where the weight has its greatest kinetic energy (and least potential energy)