Before we end this unit on water, we should do one or two demonstrations for the students with water. Ending with an activity or two might motivate them to think more seriously about an experiment/demonstration for their project.
I have found that discussing the formula H2O and then the equation:
2H2O--->2H2+O2,
is an activity of great interest to the student. The electrolysis of water demonstration gives the student an opportunity to see visually what we have been discussing. This activity can also be expanded to show how to test for the gases hydrogen and oxygen. If your electrolysis apparatus has petcocks at the top of the tubes, you can collect the gases in a test tube for testing. You might want to explain to your students this is called a decomposition reaction.
Another investigation can be done to show what is meant by a reversible equation and how the displacement method is used to collect gases. You may want to tell the student this is called a synthesis reaction.
2H2 + O2--->2H2O
In this demonstration, you fill a coke bottle with water. You then displace 2/3 of the water with hydrogen gas and displace the remaining 1/3 with oxygen gas. You cork the bottle so the gases will not escape and wrap a towel over the end of the bottle. You remove the bottle from the water, in front of an open flame (DO NOT HAVE BOTTLE POINTING AT ANYONE) remove the cork. A loud explosion occurs. Although no visible amount of water is formed, it is entertaining to the student and they do learn how to use the displacement method for collecting gases and generally remember what is meant by a synthesis reaction.
I would suggest that the teacher perform this investigation for safety reasons. If you decide to do this demonstration, the procedure for generating the gases will be your decision.
We can then go on to discuss that water can be found as a gas, liquid and solid in the same place. Have students give examples of this phenomenon. If you would like to get some practice constructing data tables and graphing results, this can be accomplished by making a data table for changing water from the freezing point to the boiling point. Record the temperature at set time intervals. When the students graphs their results, they see that this is not in a straight line but has plateaus. You may briefly talk about the heat of fusion but I would not spend a great deal of time with this area.
Think Before You Drink
We are very fortunate in the United States that we have one of the safest water supplies in the world. In Connecticut, we get about 32% of our water from groundwater and 68% from surface reservoirs. We must remain vigilant in our protection of watershed areas. Profit sometimes causes unwise decisions to be made with water shed lands which may harm the water supply.
We are told to drink from 6-8 glasses of water each day but, as we drink our daily allotment of water, we must be aware of the potential dangers that may be present. We must be aware that some possible long-term effects may result from making our water safe to drink. We must also be careful about the amount of alcohol and caffeine consumed as they can deplete water from our bodies.
