- Exp. 1-3
| Water is so omnipresent that we sometimes take it for granted. If we wanted to make a list of many sources where we could find or get a sample of water, where could we find it? Think of five sources of water. |
- Wait for a minute.
| Pick a neighbor and alternately tell each other of one source of water at a time. While we make a list of sources of water, I am going to distill water from two sources that you may have listed. |
- Put list of sources of water on the overhead.
| Water is necessary to our existence; it forms the greatest part of all natural and artificial fluids. It is present in all life forms both animal and vegetable. No matter what the source of water (river water, sea water, well water, rain water, or a colored solution); the pure water from each is exactly the same. |
- Show the distilled water from the two sources - river water and a colored solution and discuss their properties of being colorless and tasteless. Weigh a given volume of water and compare its density to some other liquids.
- Exp. 4
- Display a sample of ice.
| What physical properties do we observe? |
- Solicit answers from the students.
| Thawing ice requires much energy. Here we have a beaker of ice and a beaker of ice-water. If I pour 20 mL of hot water into each, what do you think we will observe about the temperature? Will they both have the same temperature change? |
- Exp. 6-7
- Heat of Fusion vs Specific Heat. Pour equal volume of hot water (20 mL) over beaker of ice and a beaker of ice-water (approximately 100 g in each). Measure the temperature changes in each beaker.
| How much more energy is needed to melt and raise the temperature of the ice? |
- Continue to add hot water in 20 mL increments to ice.
|More energy is required to thaw a sample of ice than to heat the same mass of water to 80°C. Why does it require more energy to melt one gram of ice than to warm one gram of water one degree? |
- Exp. 8
- Expansion of water. Fill a cast iron bomb (or whole eggshell) with water. Place in an ice-salt bath. Use a protective shield or cover around bath. Continue on with lecture while water freezes.)
|Why does ice expand when it freezes? What is happening geometrically? Why is ice less dense than water? What are the ecological consequences of this? Every winter we observe the freezing of water, which occurs at 32°F or 0°KC. |
- Exp. 9-13
- Evaporation of Water and Properties of Steam. Fill a large flask with water and boil over a Bunsen burner.
| What is this ``fluid'' that we see issuing from the flask? |
- Hold a cold watch glass near the mouth of flask to condense vapor. Hold a glass tube over mouth of flask so that steam is directed upwards. You may need to heat the tube.
| Now we see that ``hot'' steam, water vapor, is a colorless, dry ``fluid.'' If we touch the steam, it feels hot. What is producing that heat? Note the condensation occurring in the bottom of the glass tube. When water vapor is sent through this type of pipe/vessel, it produces a great amount of heat upon condensation. This is the principle behind heating pipes used in radiators. At what temperature is this condensation/evaporation taking place? Remember what happened to the egg when we turned water to ice. What will the volume of steam be like, compared to the volume of the same mass of water? |
- Exp. 14
- Inflate the Balloon. Place a balloon over the neck of the flask and fill with hot steam.
| Water vapor is very ``bulky.'' Since water expands as it vaporizes, the density of water vapor is much less than that of liquid water. One gallon of water makes 1325 gallons of steam. |
- Can do calculation: 1 in3 water --> almost 1 ft3 steam.
|Now we know water vapor takes up space - quite a bit compared to the amount required by the water. If we fill this can with steam, what will happen if we suddenly condense the steam? |
- Exp. 16
- Collapsing the can. Fill an empty soda can with about 20 mL of water. Using tongs, heat the can over a Bunsen burner until steam is readily generated and the can is filled with vapor. Quickly invert the can into a container containing ice water.
|Why did the can implode?|
| We will now discuss two aspects of chemical reactions:
- release and/or absorption of energy during a reaction
- reversibility of reactions in terms of chemicals and energy
| Before we begin let's review the terms endothermic, exothermic, hydrate, and anhydrous. |
- Attempt to elicit definitions from the students, using references to past labs or demonstrations such as hot/cold packs.
| Endothermic reactions take in energy from the environment -- feel cold. Exothermic reactions release energy into the environment - feel hot. Hydrates are a group of chemicals that have absorbed water; they are often crystalline. When the water is removed from a hydrate the substance is now said to be anhydrous -AN = not and HYDROUS = water. |
|DEMONSTRATION OF HEAT OF HYDRATION:|
- Exp. 18
- Exothermic reaction of quicklime (CaO) and water. Before class-strongly heat hard six crucibles with 5g each of CaO to dryness -- cool & cover. CaO is hygroscopic. You must have the anhydrous form. In group work areas have crucibles with DRY CaO, water bottles, and paper towels.
|You will be working in your study groups for this observation. |
- Divide class into 6 groups - assign a work station - students assign roles.
|Have students feel the temperature of the crucible and white substance (CaO). Record consensus observation. To the crucible (cool CaO) students add about 1 mL of water - have the students feel the crucible and contents again (heat of hydration). Record consensus observation. Call attention of class or bring together as a whole. What did the crucible feel like at first? |
- Call on one student.
| How many of you had this observation (cool, room temperature)? Raise your hand. Did anyone have a different observation? |
- Discuss if necessary
|Now, what happened when you added the water? |
- Call on student.
| How many agree that the crucible got hotter? Raise your hand. Why do you think that was? |
- Let students brainstorm.
| Together, let us write out a word equation for what happened. |
- Relate to the heat generated by plaster hardening. On the board write out a word equation, eliciting the information from the students. Make sure you point out where the heat goes in the equation.
|QUICKLIME + WATER = HEAT + PLASTER |
|For this second observation continue with your study group, but changing roles of recorder, etc. You should witness the next reaction for both its endothermic and exothermic behavior. |
- At each work station students will find a small test tube with a pea size crystal of copper sulfate hydrate, beral pipet, beaker of water (or water bottle, a Bunsen burner, test tube holder, and a burner striker).
|Heat only the end of the test tube with the copper sulfate with the Bunsen burner. Record the observations of the test tube noting, what changed at both ends of the tube. |
- Students should see water vapor at the top and the copper sulfate has now lost color.
| Allow the test tube to cool until you can hold it in your hands. With the pipet, add a few drops of water to the anhydrous copper sulfate. Pass the test tube around and record the group's observations. As a group, write out a word equation for both observations as we did together for part one. |
- Call attention of entire class or bring together as a whole.
| Let's share our observations. |
- List on the board.
| Now what were the word equations you came up with? What was the purpose of the Bunsen burner? Where does it fit in to the equation? |
- Call on each group.
| Okay we have heard all the groups' ideas. Now we can write them on the board together. We need two equations, why? |
- Elicit responses from students- write out word equations for each step. Again point out position of heat - Bunsen burner's purpose was to ADD heat from environment, therefore endothermic reaction. Adding water gave off heat just as did calcium oxide, therefore it also was exothermic.
| Okay we have heard all the groups' ideas. Now we can write them on the board together. |
- Call on students to write equations on the board.
| If we label these word equations, which one is endothermic, which one is exothermic? Which equation is like the one with the calcium oxide? What does this tell us? Do we need two equations, why or why not? Give me a sentence with the term exothermic. Give me a sentence with the term endothermic. Now, write a word equation to explain your observations, treating heat as a reactant or product. |
- Show it is reversible and can be written as one reaction.
| I need a volunteer to put the equation on the board. |
- Copper sulfate with water + heat = copper sulfate + water.
|Now I would like to show you another two reactions in which you should observe the change in substance and heat. Let me open this jar of sodium. Yes, I expect you have seen the sodium before, but I still find it fascinating to see a metal being stored under oil and cut with a knife. |
- Teacher then opens the bottle, using forceps takes out a piece of sodium, places the sodium on a watch glass, and cuts a pea size bit of sodium with the knife, showing this procedure to the class.
| Now I will add the sodium to the water in this beaker. Note the order of events.- Write your observations. Write an equation. |
- Teacher lists the observations being careful to note changes in substance and heat. Sodium + water = hydrogen + heat + sodium oxide is acceptable. Hydrogen + oxygen = water + heat.
|Where did the heat come from that ignited the gas released? |
|Let me show you another reaction involving water and a metal. This time the metal is common iron in the form of iron wool. Let me show you the reaction. While I put the apparatus together, you will diagram the apparatus in your notebook. |
- The reduction of iron oxide with steam involves previously gathering a steel pipe and bending the glass tubing as diagrammed. Assemble as per lab write-up included.
| Watch me put the wad of iron into the steel tube; it is fully packed but loose enough for the steam to pass through. Write the equation of iron and steam as you predict. Where will you put the heat in the equation ? Note that I start heating the Erlenmeyer flask with the water. What is the composition of the gas that first bubbles in the water bath? After the flask has been heated for a few minutes, I start to heat the steel pipe. Notice the steam generated and the steam passing down the glass tube. The steam condenses in the tube. Why have the bubbles stopped? Notice that I put the test tube filled with water over the glass delivery tube; notice the bubbles are becoming more steady even though they are smaller. As you can see, the gas has pushed out the water and I have collected a test tube worth of gas. Let us test this gas with a burning splint.|
- lights dimmed
| Watch the open end of the test tube as I insert the splint. -- Did you note the flame and small pop? As you have seen before, that is the test for hydrogen. Did your reaction look like this: iron + steam + heat = iron oxide + hydrogen? Okay let's review what we learned about exo/endothermic chemical reactions. |
- Review concepts, eliciting answers from class; use a method of total class accountability. (I.e., everyone put your heads down and get comfortable, relax, no peeking. I am going to make three comments; you hold up your right hand if the comment is correct, hold up your left hand if the comment is incorrect.)
|For homework we are going to use today's new concepts in a useful and amusing way - or so I hope. I want you to write a 1/2 page story imagining you were either the water in the copper sulfate observation or the water in the steam observation. Tell me what it would be like to experience the activity from the view point of water. Be creative.|
|You have just seen water decomposed into hydrogen and oxygen. Now let's look at hydrogen more closely. First, we have to generate some. We could use the hot iron pipe again, but this time we will simplify the process. In this flask -- |
- hold up flask --
| we have a metal, zinc, and now I am going to add some acid to it.|
- Exp. 26
- Add hydrochloric acid and stopper flask with one-holed stopper and plastic tubing to a pneumatic trough with a flask of water inverted in it.
|What is happening now? Is it boiling? |
- Call on students and ask for their opinions and why.
| We all agree (after much convincing) that we are producing a gas and most likely hydrogen since that's what we started to talk about. |
- By this time two flasks should be filled with hydrogen gas. Cover one flask and hold it up.
| What are some properties of this gas? |
- Generate a list of the physical properties of hydrogen gas, including transparent, colorless, insoluble in water, less dense than water, not acidic or basic by testing with pH paper.
| We all agree that hydrogen is less dense than water, but what about air? Is hydrogen gas more or less dense than air? |
- Exp. 32
- Turn flask of hydrogen upside down and remove top. Take second flask and pour upwards into another flask.
| Now let's test to see where the hydrogen is. |
- Exp. 27
- Ignite one flask with Bunsen burner.
| Hydrogen is clearly flammable, explosively so. Notice also that we get some cloudiness in the flask; what is it? That's right, we made water. Now imagine that we mix hydrogen and pure oxygen and ignite it. But first cover your ears. |
- Exp. 34
- Pour out some hydrogen/oxygen soap bubbles and ignite.
|We have just studied one of the constituents of water, hydrogen. But water is a two-part system; the other part of water is oxygen. With a procedure called electrolysis, we can separate water into two distinct parts using electrical energy from this power source. This is a modern version of a Wollaston's apparatus. The water is colored with phenol red, an indicator which is red in basic conditions and yellow under acid conditions. As the electrolysis proceeds, note the relative amounts of products that are formed at each electrode. Make at least three observations about the system. |
- Exp. 17,37
- Give the students time to write down their observations. After a few minutes take time to solicit observations from the class. Important observations might include the following: 1. The products are both gaseous. 2. The relative volumes seem to be in a 2:1 ratio. 3. The gases are both clear and colorless.
| We already know how to test for several gases. Let's first do a splint test on each of the gases formed. Listen and watch the glowing splint carefully in each test. |
- Do a flaming/glowing splint test on each gas. Make sure that you clearly indicate from which side of the electrolytic device you draw your gaseous sample.
| Can you make a hypothesis about the identity of each of these gases? |
- Solicit answers from the class.
| Upon what physical evidence do you base your hypothesis of the identity of the gases produced? |
- The difference in the splint test for the two gases should yield hydrogen and oxygen identified as the two gases. Make sure that the correct label is associated with each electrode. The student should make an association of hydrogen with the gas of greater volume collected.
| Now that you've identified hydrogen and oxygen, what product do you think will form when hydrogen burns in air? |
- Exp. 39
- Condense the water vapor that is emitted from a burning jet of hydrogen with a cold surface, i.e. a mirror. Wipe your finger across the wet surface, as per a mirror in a bathroom.
| Since oxygen is present in air, burning hydrogen in air gives evidence of water formation in the form of condensed vapor. Studies can be made about these two gases that make up water. We have tabulated the results here on this table. What generalizations can you make about the system? |
- Allow time for the students to review and make statements about the xerox copies of the tables that are distributed. They should note that the relative ratio in the various tests consistently yields a volume ratio of 2:1. The volume ratio of 2:1 is not mirrored in the ratio of the relative weights which is 1:8. Little attempt is made at this time to make comprehensive statements about the reasoning for these ratios. It is sufficient that the students realize that these ratios exist.
|We can see that although there is a smaller volume of oxygen, this lesser volume has a greater mass than the hydrogen. We've seen previously that hydrogen is indeed so light that it pours upward. When water is decomposed, two volumes of hydrogen are produced for each volume of oxygen. |
| Now that we have separated water into its component parts, what do you think will happen when we spark a mixture containing 2 volumes of hydrogen to 1 volume of oxygen? What will the product of the reaction be? Look at the demonstration sheet in front of you and jot down a few responses to the questions listed. Remember the soap bubbles from the last part of the lecture? Let's watch this video. |
- Exp. 38
- The students should have a student-version of the lab sheet: The Synthesis of Water. Perform the demonstration as written.
| What have we seen? The product of the reaction is water. |
- The teacher has the option now of having the students do the lab report as a written or oral assignment. In this case we will chose the former.
|The loud sound we just heard is evidence of large amount of energy resulting from the recombination or the combustion of hydrogen and oxygen. Here's more evidence of the energy released during this combustion reaction. |
| Indeed, normal combustion also gives evidence that hydrogen is contained in common fuel sources as when combusted they too combine with oxygen from the air to yield water. |
- Exp. 41
- Place a cold glass surface near to the source of the flame. Observe the resultant condensation.
| Can you see that this cloudy film is indeed water? Just as we've seen before, water is a product of other types of combustion. |
- Refer the students to the page titled ``SUMMARY'' in the handouts for the lecture. Verbally go through the blanks on the sheet. Try to solicit answers from the students as much as possible. Encourage them to review notes they have taken during the lecture. Going through the summary sheet is sufficient closure to the lesson.
Pam Fujinaka, George Hussey, Jeffrey M. Green, Edgar Johnson, Michael J. Kelly, Cristina Kerekes, Louise Komp, Patty A. Kreikemeier, and Daniel Lane.