Assignment 7

1. Alkaline Earth Metal of the Week

Calcium is the chemical element with the symbol Ca and the atomic number 20. It has an atomic mass of 40.078. Calcium is a soft grey alkaline earth metal and is the fifth most abundant element by mass in the Earth’s crust.

Calcium is essential for living organism, particularly in cell physiology, where movement of the calcium ion Ca2+ into and out of the cytoplasm functions is a signal for many cellular processes. As a major material used in mineralization of bones and shells, calcium is the most abundant metal by mass in many animals.

Calcium is the fifth most abundant element by mass in the human body, where it is a common cellular ionic messenger with many functions, and serves also as a structural element in bone.

Chemically calcium is reactive and soft for a metal (though harder than lead, it can be cut with a knife with difficulty). It is a silvery metallic element that must be extracted by electrolysis from a fused salt like calcium chloride.
Calcium salts are colorless from any contribution of the calcium, and ionic solutions of calcium (Ca2+) are colorless as well. Many calcium salts are not soluble in water. When in solution, the calcium ion to the human taste varies remarkably, being reported as mildly salty, sour, "mineral like" or even "soothing." It is apparent that many animals can taste, or develop a taste, for calcium, and use this sense to detect the mineral in salt licks or other sources. In human nutrition, soluble calcium salts may be added to tart juices without much effect to the average palate.

Calcium is not naturally found in its elemental state. Calcium occurs most commonly in sedimentary rocks or in the minerals calcite, dolomite and gypsum. It also occurs in igneous and metamorphic rocks chiefly in the silicate minerals.
Calcium, combined with phosphate to form hydoxylapatite is the mineral portion of human and animal bones and teeth. Foods such as milk and cheese, are a well-known source of calcium. However, some individuals are allergic to dairy products and even more people, particularly those of non Indo-European descent, are lactose-intolerant, leaving them unable to consume non-fermented dairy products in quantities larger than about half a liter per serving. Others, such as vegans, avoid dairy products for ethical and health reasons. Fortunately, many good sources of calcium exist. These include seaweeds such as kelp, wakame and hijiki; nuts and seeds (like almonds and sesame); blackstrap molasses; beans; oranges; figs; quinoa; amaranth; collard greens; okra; rutabaga; broccoli; dandelion leaves; kale; and fortified products such as orange juice and soy milk. An overlooked source of calcium is eggshell, which can be ground into a powder and mixed into food or a glass of water. Cultivated vegetables generally have less calcium than wild plants.

2. Avogadro’s Hypothesis

This was an interesting web site. I thought Avogadro’s Principle was a theory, not a hypothesis. Am I to assume from this web site that his principle is tentative? (meaning it has not yet been well tested?) Is it being modified when results are not as expected? Since it is not yet a theory, I guess it has the possibility of being wrong. How many times does a hypothesis need to be successfully tested before it is considered a theory?

3. What is the mole? - Review of link

I did not find this link to be particularly helpful. The long-winded narrative style lost me by the second paragraph. I think more graphic examples would help facilitate my understanding.