(MAM) Water Lesson

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H20- aka - Water }

bio19_wateronpenny.jpgTake a penny, dropper, and a cup of water.

How many drops of water do you think the side of the penny can hold? That is your hypothesis.

Then, start dropping water slowly one drop at a time. How many drops did you get? Were you surprised?

You will learn about why this happened as you progress through this lesson.

We Need Water!

All living things depend on water. Water covers 70% of the Earth and is the most abundant compound in living things. Read through the following notes to learn more about the special properties of water.

You'll Need a Drink With That Sandwich!
bio109_sandwich.png Let's pour a nice glass of water to drink while you eat that sandwich. Just make sure it's got the right pH balance first!

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Scientists have devised a scale to measure the concentration of hydrogen ions (H+) and hydroxide ions (OH-) that exist in solutions. The scale is called the pH scale. The pH scale ranges from 0 to 14.

  • Neutral solutions have equal amounts of H+and OH- Neutral solutions have a pH of 7.
  • Acids, or acidic solutions, have a greater amount of H+ and are assigned a number between 0 and 7 on the pH scale. The lower the number, the more acidic the solution.
  • Bases, or basic solutions, have a greater amount of OH-, (or less H+) and are assigned a number between 7 and 14 on the pH scale. The higher the number, the more basic the solution.
  • pH is measured on a logarithmic scale. This means that the difference of one pH unit (example: between 3 and 4) means that there is a tenfold difference in H+or OH-

Water is SO Basic!

Take a look at the picture on the right that shows the pH scale and common substances with each pH level.

All living organisms have a set range of pH levels that are optimal for their growth and development. Sudden changes in pH levels can harm organisms. The pH inside human cells must be kept close to neutral in the range of 6.5 to 7.5. If a chemical with a lower or higher pH enters the cell, it could disrupt chemical reactions and cells' homeostasis. Substances with a very low (strong acid) or very high (strong base) pH cause chemical burns. To combat this, cells contain weak acids and weak bases called buffers which work to neutralize substances inside cells that are too acidic or too basic.

Acid rain is is a concern for biologists because it can harm living things. It damages trees at higher elevations and can create an acidic environment for organisms in streams and lakes. It results when rain combines with waste chemicals in the atmosphere from cars or power plants (sulfur dioxides or nitrogen oxides). Acid rain has a pH of around 4.

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Water Challenge and Before You Go

Practice Time! Use the knowledge you learned from the lesson to complete the practice activities below.

Before You Go You Need To Know

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The following key points are from the explore section of the lesson. You must know the following information before moving to the next lesson. This is just a summary of the key points.
  1. Why is water polar?
    • It has an uneven distribution of positive and negative charges.
    • The hydrogen end has a slightly positive charge, while the oxygen has a slightly negative charge.
  2. What are some special properties of water?
    • Adhesion, cohesion, polarity, capillary action, the high heat of vaporization, surface tension
  3. What does the pH scale measure?
    • How much hydrogen and hydroxide ions are present in a substance.
    • If there are more hydrogen ions, then it’s an acid.
    • If there are more hydroxide ions, it is a base.
    • If there are equal amounts, it is neutral.

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