Humboldt State University ® Department of Chemistry

Richard A. Paselk

	Science 331
Fall 2004	Lecture/Activity	Office: SA560a
Notes: 18 October		Phone: x 5719 Home: 822-1116
		e-mail: rap1

Matter

What is matter? Stuff. Has mass and occupies space.

Mass: The measure of quantity for matter. Mass is the property of matter resulting in its inertia and and attraction via gravity.

• Do not confuse mass and weight. Weight is the force acting on an object due to gravity. We often interchange these terms in conversation, but they are quite different - you have the same mass whether you are weightless in space on here on Earth (taking a shuttle flight is no substitute for a diet!). To confuse us further we call the determination of mass "weighing"!

Matter has both physical properties and chemical properties. These are properties which do not depend on the quantity of substance and therefore they can be used to identify a substance (sometimes referred to as intensive properties).

• Physical properties of substances can be observed without, in principle, changing their compositions. Physical properties include mass, color, density etc. Note that physical changes such as melting, cutting, etc. do not change composition, that is new substances are not created, old substances are not lost. At the microscopic level, the relationships of atoms to one another are unchanged.

States of Matter. Matter can exist in three states under earth-surface conditions:

• Solid: definite shape and volume (Crystals vs. super-cooled liquids or glasses)
• Liquid: definite volume, but no defined shape - will fit to container etc.
• Gas: no definite shape or volume - will fill whatever container they are in.
  • both liquids and gases are fluids.

A fourth state of matter commonly occurs under special conditions: a plasma. A plasma is an ionized fluid - can be contained by magnetic fields.

• Chemical properties of substances describe behaviors which lead to changes in composition. Chemical properties describe reactivity under various circumstances (does it burn in air, react with acids or bases, corrode in sea water etc.) Note that chemical changes result in different compositions - substances are transformed to new things. Inparticular, the relationships between atoms are changed.

States of Matter and Changes of State

Matter can exist in three states (phases) under earth-surface conditions:

• Solid: definite shape and volume (Crystals vs. super-cooled liquids or glasses)
• Liquid: definite volume, but no defined shape - will fit to container etc.
• Gas: no definite shape or volume - will fill whatever container they are in.

Liquid Nitrogen Demo-balloons, Pb bell, rubber tubing, scatter on floor, pour over hand etc.

Exercise-Changes of State in Water

A common form of matter exhibiting these states under lab conditions is water. Let's look at water starting in its solid state and observe its transitions. We'll use the following equipment:

• Heat source (bunsen burner)
• Beaker
• Thermometer
• Test tube
• Scale
• Ice

So let's all melt some ice and observe what happens:

• Set up your bunsen burner, ring stand and wire screen as demonstrated by instructor.
• Light your burner and adjust the flame using the needle valve and air adjustments on the burner . Make sure the gas cock is fully open.
• Do not adjust the burner further during the experiment. You may turn the burner off and on at teh cock, as long as you always turn it fully on or off. This way we have a continuous, constant heat supply.
• Time all of the heating steps below.
  1. Fill beaker with ice, measure temperature and weigh.
  2. Melt partially, measure temperature. record times and temperatures
  3. Continue measuring temperature as ice is heated and melts. record times and temperatures
  4. When ice completely melted, weigh again.
  5. Note temperature change as liquid water is heated. record times and temperatures
  6. Note temperature as water boils.
  7. Hold a test tube containing ice above boiling water, NOT in steam, and observe what happens. record times and temperatures
  8. Stop boiling, weigh again.

What can you say about what has happened? e.g.:

• Do you think mass was conserved? Why?
• Was the water changed? Explain.
• Is ice a true crystalline solid? Why or why not?
• Make a plot of energy or heat added (time) vs. temperature (a heating curve similar to figure 2.5 on p 67 of your text).

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© R A Paselk

Last modified 25 October 2004