Description of the Experience
Opis skúsenosti I teach water immediately after hydrogen, because it is hydrogen’s most extended composition. Students take water as something granted as well as something that you can not say anything really new about. They usually take it as a substance they use when necessary, to drink and wash themselves with. The girls sometimes recall cooking.
In one of the popular scientific publications that I read long time ago, I received information on the topic that interest students.
Water is the strangest compound of our planet. It exhibits a number of anomalies that permits life in the form we know. One water molecule is unable to exist alone. Only so called water molecule associations exist. Water violates the law of density dependence on temperature and has the highest density at about 4 degrees Celsius, causing that water bodies do not freeze all the way to the bottom. Then with the students we discuss the imaginary situation what would happen if all the water bodies freeze to the bottom. First they imagine that in the spring all the ice would melt and everything would start again. Only after a while they gradually begin to realize the amount of extinction of living organisms, i.e. plants and animals and as a result the inevitable changes of life on Earth, or even its possible termination and/or disruption of the food chain.
Another interesting fact is that ice as a solid state of water is less dense than water. Think of glaciers of which 9/10 is submerged under the water level and only one tenth is visible. After this fact starts a heated debate about the Titanic crash, which sank off thanks to a collision with an iceberg. All have seen the movie and according to the situation in the class we ended up discussing Leonardo di Caprio and the American film industry and art in general.
To the topic of water I devote two lessons, so we can wander off into its all possible areas. The water we get from ice has different characteristics than the one that was originally in the liquid phase. It is so partially because it still holds its crystalline structure.
My students come mostly from an environment where breeding hens is common, so I recommend them the following experiment: one group of chickens will get water derived from ice and the other one ordinary water. The animals of the first group will thrive better.
Mr. Celsius used water to create the temperature scale. He designated the boiling water point as 0 degrees and the freezing point as 100 degrees. The class soon begins to protest that I have made a mistake, but I did not. Only one of Celsius’s students turned the scale around into what it is today.
It is important to remind them the topic of solutions, because water is the most common solvent. We begin to analyze how to wash off oily stains. No one in the class knows it. Then we begin to discuss the history of washing starting washing with cold water in the streams to modern advertising for detergents and advertising at all.
It is of interest to them that a person, which weighs about 70 kg, has in himself about 40 kg of water. They make various comments on it... someone has in himself a beer...
Our chemistry textbook was made in 1985. Graphically it is ugly. It consists of only dry facts, students do not want and do not know how to learn from it. They have problems with element symbols and I do not even want to mention writing chemical formulas or solving chemical equations. In a similar way it is not relevant to explain to them why the water molecule acts as a dipole. They immediately see it as "this is a school form that is boring and poisoning".
They know what types of water treatment exist- drinking, service etc. However, it is interesting to discuss with them about the mineral waters. They have no idea where these waters come from and that these species should be varied in order to get into the body all the elements that are necessary.
I also teach them how to, in a few seconds, determine whether there is or there is not enough water in your body: catch the skin on your hands with two fingers. If it is elastic it means there is enough water in the body. If the skin does not return to its original position, the body does not have enough water.
My experience teaching this topic is positive. The class itself speaks about the future of water as a precious substance. They also have additional questions.
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