Every time I open the faucet to wash dishes or drink some water, I have to remind myself of the fact that thousands of people, mostly women, all over the world, are right now searching for/storing water and fuel for their daily survival. I also think of California now using gray water (water used for washing/bathing) whenever possible to water gardens after going through a severe drought and forest fires. Water is such a precious commodity but we take it for granted when there seems to be plenty available. All trees, plants, animals need this liquid to survive but a tree like the weeping willow, would hardly grow without a constant flow of water.Today we will look at water, first as a chemist and then its significance in 19th century England.
A water molecule (a molecule is a combination of atoms) is made up of two atoms of hydrogen and one atom of oxygen and the chemical formula is written as H2O. The structure is planar (unlike methane, CH4 , which is 3-dimensional, a tetrahedron) and can be depicted with the H-O-H angle as 1050
and is shown as:
Also, the molecule is polar since the electronic cloud in each bond, moves a little closer to the oxygen atom and therefore the hydrogen atom is slightly positive(δ+) and the oxygen atom is slightly negative (δ-). This allows the different molecules of water to form a connection with each other like this:
This is called hydrogen bonding.
Water has some unique properties because of its polarity; it dissolves many solids and is used as the first test to detect chemicals in the laboratory: is the substance soluble or insoluble in water? Water is called the universal solvent and allows us to absorb many nutrients when we eat, because they dissolve in water readily. Substances that dissolve in water are called hydrophilic and those that repel water( like oil) are called hydrophobic.
Water exhibits cohesion, adhesion and surface tension as well because of its polarity. Cohesion means water sticks well to other water molecules and adhesion means that water sticks to other substances as well. Because of adhesion, water spreads out well on a glass plate. The high surface tension of water leads to more of cohesion versus adhesion causing water to act like the surface is a stretched transparent plastic sheet. Surface tension is why water beads up on a waxed car or on the surface of leaves/fruits (that have a waxy, oily surface) after a rainfall, or when you wash them.The meniscus of water is curved such that it has a concave shape, more on the sides of the container and less in the middle, away from the container. Adhesion and water’s high surface tension are responsible for the shape of the meniscus.
The hydrogen bonding leads to some unique properties as well. Water has a very high specific heat, which means it takes a long time to heat up. (I will talk again about specific heat later) But to me, the most interesting and useful application of water is in the way it freezes. All liquids, when they cool down sufficiently become solids and almost always the solids are denser than their liquid form, which means they will sink to the bottom of a container containing the liquid. Water, however, behaves differently. As you start cooling water, the density (ratio of mass over volume) increases, but at 40C it starts getting less dense. (Remember that water freezes to ice at 00C)This has a lot to do with the lattice-like structure due to hydrogen bonding that leads to a lot of open spaces between the water molecules.(When volume increases, density decreases.) So, when the weather gets cold and the local pond or river starts freezing, the ice forms a layer on the top, does not sink down and all aquatic life continues to live in cold weather,since the water body does not freeze solid; amazing!
In the middle of the 19th century, London was already a very congested city. The book, The Ghost Map, written by Steven Johnson, is a true account of the mysterious high number of deaths that was happening suddenly in a part of London. At that time, the prevalent notion was that because there were many people living together, there was ‘bad air’ that caused this epidemic. However, a physician Dr Snow, figured out where the deaths were taking place and did a detailed mapping of that area to find out that the abnormal high mortality rate was because of contaminated drinking water from the same source; a water pump. For the first time, a water-borne disease like cholera were correctly diagnosed. As you can see here, water the universal solvent, can also lead to terrible consequences.
Activities for Middle School Teachers: Work collaboratively with the math instructor on gathering statistical data (like the data collected by Dr. Snow in the book) .
You could also collaborate with the Social Studies instructor to read the book The Ghost Map to understand the importance of water in figuring out how the epidemic spread.
During the early winter season, take students on a field trip to view lakes, ponds that have a thin upper layer of ice. Ask students, “Why do ice cubes float and not sink in water?” Take students to the nearest water filtration area for them to understand how local water is purified.Students can learn how to measure the volume of water in a measuring cylinder by looking at the lower meniscus at eye level. In addition, students could improve their geography skills and locate big cities around the world close to a water source.
Nuggets of information: Stop drinking bottled water, you are wasting money and adding more plastic to the environment.The water is not any different from tap water, and is slightly treated. Contrary to popular belief, this bottled water does not come from some mysterious sparkling spring somewhere.
John Snow mentioned in The Ghost Map,is considered the Father of Epidemiology. This means the science of the patterns , causes and effects of diseases and health in a defined population.
References:
http://science.howstuffworks.com/environmental/earth/geophysics/h2o7.htm
The Ghost Map The Story of London’s Most Terrifying Epidemic — and How It Changed Science, Cities, and the Modern World
by Steven Johnson Riverhead Books, New York, 2006.
http://www.alternet.org/environment/bottled-water-americas-destructive-love-affair
Chobhi's Blog 
September 22, 2015 at 1:35 pm |
Oh, my, how much I learned from this!
September 22, 2015 at 4:07 pm |
Glad to know you enjoyed and learned from my blog Glenda!