Properties of water worksheet
Critical Reading: pH
When some substances dissolve in water they break up into ions. A compound that releases a hydrogen ion (a proton) when it dissolves in water is an acid. Bases are compounds that remove, or accept, hydrogen ions. A solution’s acidity, or its hydrogen ion concentration, is measured on the pH scale. An acid has a low pH (pH 0-7) and a high hydrogen ion concentration. A base has a high pH (pH 7-14) and a low hydrogen ion concentration. Organisms must maintain a stable pH. Even a small change in pH can disrupt many biological processes. Pure water has a neutral pH of 7.
1. What does an acid release when it is dissolved? ___________________________
2. What does a base release when it is dissolved? ____________________________
3. What does a base remove or accept? ______________________________
4. What is a solution’s acidity? ___________________________________
5. Describe what the pH of a substance is measuring.
12. Draw the pH scale using numbers and label acid, neutral, and base. (Using numbers 0-14)
13. What has more hydrogen ions, acids or bases? ____________________
14.A student mixes strawberry koolaid and water. A pH meter is used to measure pH of 5.4. What kind of solution is strawberry Koolaid? _____________________
15.In the koolaid mixture, what must there be more of, hydrogen ions or hydroxide ions? _______________
16. A student adds an alka-seltzer to the koolaid and stirs. The pH meter now reads 8.3. What was released by the alka-seltzer tablet to cause this change?
17. Label each of the images below as acidic, neutral, or basic.
[pic] [pic] [pic]
______________ ______________ _______________
18. Label each situation as an acid or a base.
Situation pH Acid or a Base?
|Water directly out of tap |pH =7.2 | |
|pH after exhaled air is blown through a straw into water for 5 min. |pH=5.1 | |
|pH after a snail has lived in water for three days |pH=5.8 | |
|pH with 2mL of bleach added to the water |pH=9.4 | |
|pH with instant coffee added to the water |pH=5.0 | |
|pH after an aquatic plant is grown in water for three days in bright sunlight |pH=7.7 | |
a. What effect does carbon dioxide have on tap water?
b. Which situation is the most basic? ___________________
c. Which situation is the most acidic? ____________________
Critical Reading: Buffers
A buffer is a mixture of molecules that release or bind H+ in order to maintain a relatively constant pH. Most buffers consist of a weak acid (which releases H+) and a weak base (which binds H+.) Note that the function of a buffer is NOT to keep a solution neutral (at pH 7); its function is to minimize the change in pH when base or acid is added to the solution. Buffers are extremely important to living organisms because most biochemical processes proceed normally only when the pH remains within a fairly narrow range. An excess of H+ or OH- can interfere with the structure and activity of many biomolecules, especially proteins. Therefore, buffers are commonly used in living organisms to help maintain a relatively stable pH. In humans, for example, buffers act to maintain blood pH between 7.35 and 7.45 even though acids and bases are continually being added to and removed from the blood as it travels through the body. If the pH goes above the normal range it is called alkalosis and if the pH goes below the normal range it is known as acidosis.
19. Describe a buffer.
20. Why are buffers important to the human body?
21. Look up acidosis and list some side effects.
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