Physical and Chemical Properties and Changes - Download Now DOC by IJ6ol2uG


									                             Physical and Chemical Properties and Changes

The universe around us is composed of a wide variety of different substances. Each individual substance
can be characterized by a specific set of physical and chemical properties. Physical properties are those
characteristics that can be observed without an accompanying change in the composition of the substance,
such as physical state, density, boiling point, and melting point. Chemical properties, on the other hand,
always result in a change in the composition of the substance, such as burning, digestion, or rusting metal.
Running tests on them to determine their individual characteristics can identify substances.
In addition to physical and chemical properties, substances can be characterized by the physical and
chemical changes that occur. A physical change, such as boiling, will not change the composition of the
substance; however, a chemical change, such as burning, will produce new materials as a result of the
reaction. Pure substances can be characterized by looking at a combination of their physical and chemical
properties and any physical and chemical changes that they have.

Copper wire is reasonably inert.
Iodine is toxic if inhaled or ingested and will cause skin irritation if spilled.
Potassium chlorate is toxic if ingested. It may cause fires if exposed to combustible materials. Wash
excess down the drain.
Sodium chloride is reasonably safe except in large amounts.
Sugar is innocuous (but fattening)
Magnesium ribbon will burn violently when exposed to flame. Place excess in labeled waste container in
hood after use.


Many physical and chemical changes require heat. All of the experiments to be performed here will require

Section One

Weigh a crucible and lid on the top-loading balance. Place a large piece of steel wool in the crucible and
reweigh it. Heat it on a clay triangle gently at first and then intensely for thirty minutes. While your steel
wool is being heated, proceed to the next section of the experiment. Once your steel wool has been heated
for thirty minutes, remove it from the heat and put it into a desicooler to cool for thirty minutes. Then
reweigh. What change in weight and appearance did you observe? What does this indicate?

Section Two

Pieces of copper wire, and magnesium ribbon (approximately 2 cm long) will be examined first. After
recording the initial appearance of each metal, use a crucible tongs to hold the piece of metal in the hottest
part of the Bunsen burner flame. Hold the metal in the flame until it becomes red-hot, then remove it and
note any changes that have occurred in its appearance. Compare it to the original appearance. If a
chemical reaction occurred, give the reaction equation for it. (Caution: the magnesium ribbon reacts
violently! Do not look directly at it!)

Section Three

Put a small amount of sodium chloride (NaCl) in a pyrex test tube and hold it in the flame. Record your
observations. If a chemical reaction occurred, write the chemical equation that shows the reaction.
Repeat the above procedure for sugar (C12H22O11), and potassium chlorate (KClO3). Record your
observations in each case and write a reaction that shows any changes that occurred.

    1.    Compare the energy content of the magnesium ribbon with its residue.

    2.    Copper appears to have undergone a chemical change when heated. What accounts for this
          observation and how could you prove it?

    3.    Give an example (do not use the ones from the experiment) of each of the following:
              a) another substance that undergoes a physical change
              b) another substance that undergoes a chemical change

    4.    Does the solid that remains in the test tube after heating the potassium chlorate weigh less, more,
          or the same amount as it did before it was heated? Explain your answer.

Data Sheet

   Mass of crucible plus steel wool       =    ____________g

    - Mass of empty crucible     = _____________g

    Mass of steel wool                     = _____________g

    Mass of crucible plus steel wool after heating    =   ____________g

    - Mass of empty crucible              = _____________g

       Mass of steel wool after heating              = ______________g

Explain the change in appearance and the change in mass.

Data Table

                        Physical      Chemical
Substance               change        change           Reaction

Mg ribbon

Cu wire




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