Properties of Matter: Investigation 2 –
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Remind students that by observing a sample of matter and measuring its chemical and physical properties, we gradually acquire enough information to characterize it and distinguish it from other kinds of matter. This is the first step in the development of chemical science, in which interest is focused on specific types of matter.
Explain to students that chemists may develop a synthetic fiber that can stop a speeding bullet or figure out how to make hair-styling gel work better.
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Tell students that during the presentation they will
- review the concepts of matter, elements, molecules and compounds,
- learn about density as a property of matter, and
- learn about the concept of chemical change.
Note: Students will perform chemical reactions on the six unknowns that they have in Lab for this Investigation.
Note: This slide has animation.
- Tell students that this slide reviews the relationship of the terms introduced in Investigation 1.
- Review the following with students:
- Matter: Remember that everything with mass and volume is matter.
- Elements: All elements are matter. There are 118 different elements currently known.
- Atoms: Elements are composed of Atoms. Atoms are the smallest unit into which an element may be broken down to that still retains the element’s characteristics.
- Molecules: The next click takes us from atoms to molecules. Atoms may interact with each other to form molecules.
- Compounds: If there are more than one type of atom in a molecule (that is, atoms of two or more different elements) we can refer to the molecule as a compound. Note: Remember a compound is still a molecule, its just a special kind of molecule because it contains more than one type of atom.
- Subatomic Particles: This is just another reminder to students that atoms are not the smallest particles and that atoms themselves are composed of even small bits of matter. Notice that all of the terms on the slide all fall under the category of matter.
Note: This is the same slide we used in Investigation 1. It shows one element, oxygen.
- Review this slide emphasizing that oxygen atoms may combine to form molecules and compounds. Also review that the oxygen atom is made up of smaller “subatomic” particles.
- Tell students that, just like the oxygen slide in Investigation 1, this slide uses the element sulfur as an example to build a molecule from an atom and to accentuate the difference between a molecule and a compound.
Note: The concept of subatomic particles is once again presented in this slide.
- Explain to students that
- every atom contains a “nucleus” containing the same number of the subatomic particles protons and neutrons in most cases, and
- an atom’s nucleus is surrounded by a cloud of electrons that are present in the same number as protons as well.
Note: The number of protons gives us the atomic number on the Periodic Table of the Elements – there are 16 in the case of sulfur.
Note: The number of protons plus neutrons gives us the approximate “Atomic Mass” of the element as shown below its symbol on the Periodic Table.
- Tell students that
- the molecule sulfur is a yellow solid that they will work within many LabLearner labs in the future, and
- sulfuric acid (H2SO4) is a liquid that they will also become familiar with in later labs.
- Remind students that they determined the mass and volume of their six unknown samples.
- Explain that they will use their mass and volume data to calculate density using the formula of D = m/v
- Tell students that the units for density are g/cm3 (grams per cubic centimeter)
- Share the example calculations with students.
Note: The example on the left gives a density of more than 1 g/cm3 and the one on the right gives a density of more than 1 g/cm3. The density of water is 1 g/cm3. Therefore, an object with a density greater than 1 g/cm3 may be expected to sink in water whereas an object with a density less than 1 g/cm3 may be expected to float.
Note: This may be a bit confusing to students since other factors can enter into determining whether an object will sink or float. For example, battleships are made of steel, which is much denser than water. However, the battleship floats because of the shape of its hull that captures a large volume of air, which is much less dense than water. These concepts will be discussed later in LabLearner.
Note: A bit more about cubic centimeters (cm3): Recall that volume is three-dimensional. If we measure a cubic centimeter block, we would find that its length is 1 cm, its height is 1 cm and its width is 1 cm. We would then multiply these dimensions together (1 cm X 1 cm X 1 cm) and get 1 cm3. Also note that:
- In medicine, a cubic centimeter is sometimes abbreviated as cc.
- More importantly for us at this point is that a cubic centimeter of volume is the same as a milliliter (ml) of volume. Thus, when one measures 20 ml of a liquid in a graduated cylinder, you also have a volume of 20 cm3.
- Liquids volumes are nearly always reported as ml or liters.
- Solid volumes are nearly always reported as cubic centimeters (cm3) or cubic meters (m3).
- The volume of gases is often reported as either cubic meters or liters, etc.
- Explain to students that this slide shows how mass and volume (volume displacement method) are measured in the lab. Remind students that they should be familiar with these techniques.
- Share the example calculation with students.
- Discuss potential sources of error in measuring mass and volume in the lab (listed below).
- Air current in the lab causes the balance to be unsteady and moving.
- Balance not sitting flat and evenly on the bench.
- Forgetting to subtract the weight of the weighing dish, centrifuge tube, or other container used to hold the sample.
- Operator error (i.e. student misread the balance, mathematical errors)
- Misreading ruler if determining volume by dimensions.
- Using volume displacement method:
- Trapped bubbles in sample
- Sample doesn’t completely sink
- Operator error (i.e. misreading calibrations on the graduated cylinder, mathematical errors)
- Explain to students that this slide reviews physical and chemical properties and introduces the concept of a chemical reaction.
- Discuss the concept of a chemical reaction emphasizing the concept of elements, atoms and molecules when discussing chemical reactions.
- Note: We want to be sure that in the excitement of the lab, students do not loose sight of the fact that chemical reactions we observe are simply macroscopic indications that atoms and molecules are rearranging themselves!
- temperature change,
- gas formation, and
- color change.
Note: There are only a few examples of evidence that a chemical reaction has occurred and may be observed in Investigation 2. Other evidence of a chemical reaction include (there are others):
Discuss the three forms of evidence of chemical reactions included on this slide:
- Formation of a solid when two liquids are mixed (state change, precipitate)
- Light given off
- Sound is produced
- Change in odor
- Change in taste (we don’t use this in the lab!)
- Change in pH
- Change in viscosity