Monday, May 2, 2011

Welcome Back! (to chemistry)

Over the next two weeks we will be reviewing some of the chemistry we learned at the beginning of the year, as well as going into more depth on the structure of molecules. This information is NOT in your textbook, so you will have more class handouts use additional websites.

Today we talked about what elements make up the human body and their functions, as well as how these elements compare to the elements in the Earth's crust. We also learned about the properties of water.

Homework: Read each statement below and explain (in 2-3 sentences per statement) how the properties of water are related to the phenomena that are described. More than one property may be used to explain a given phenomena.

1. During the winter months, air temperatures in the northern United States can remain below zero deg. C for months; however the fish and other animals living in the lakes survive.

2. Many substances, for example salt, dissolve in water very quickly.

3. When you pour water into a 25 mL graduated cylinder, a meniscus forms at the top of the water column.

4. Sweating and the evaporation of sweat from the body surface help reduce a human's body temperature.

5. A bottle contains oil and water. You shake the bottle vigorously and put it on the table. Over time, the oil and water separate.

6. If you touch the edge of a paper towel with water, the water will move up into (or be absorbed by) the towel.

Here's a reminder of some of the properties of water:
Life as we know it could not exist without water. All the chemical reactions of life occur in aqueous solution. Water molecules are polar and are capable of forming hydrogen bonds with other polar or charged molecules. As a result, water has the following properties:

A. H2O molecules are cohesive; they form hydrogen bonds with each other.

B. H2O molecules are adhesive; they form hydrogen bonds with polar surfaces.

C. Water is a liquid at normal physiological (or body) temperatures.

D. Water has a high specific heat.

E. Water has a high heat of vaporization.

F. Water’s greatest density occurs at 4°C.

Here's a link about water & hydrogen bonds that you might find helpful.

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