Module+1+Chapter+2+Pages+24-31

C. The **__pH__** scale is used by scientists to represent the nature of a solution relative to the amount of hydrogen ions in solution. The scale extends from a numerical value of 0 to **__4__**.
1. Solutions with a value of "0" are very __**acidic**__, meaning there is a high concentration of hydrogen ions in solution.

2. Solutions with a value of "14" are very **__basic__** (alkaline), meaning there is a very low concentration of hydrogen ions in solution.

3. Pure water has a value of **__"7"__**, which indicates it is a neutral solution, or in other words one with the same amount of H+1 and OH-1 ions.

4. The pH scale is a type of metric scale. This means that for every change in the pH, there is a ten-fold change in the concentration of hydrogen ions. On the metric scale, to change from one unit of measurement to another it is necessary to move the decimal point either to the right or to the left. Each time the decimal point is moved it is equal to multiplying or dividing by 10. If the decimal moves 3 places to the right it is equal to multiplying the value by 10 X 10 X 10 or the final answer is 1,000 times larger. The following are several examples:

A solution with a pH = 2 is 10 times more acidic than a solution of pH = 3. A solution with a pH = 5 is 100 times less acidic than a solution of pH = 3. A solution with a pH = 10 is 100 times more basic than a solution of pH = 8. A solution with a pH = 6 is 1,000 times less basic than a solution of pH = 9.

D. **__Salts__** are substances that when dissolved in water release ions other than the hydrogen ion (H+1) or hydroxide ion (OH-1). Examples include sodium chloride or table salt (NaCl) and calcium phosphate [ Ca3(P04)2 ] found in bones. Most salts serve key functions in cells. The ions released into solution int he body are also called "electrolytes", in that they allow the solution to be able to conduct an electric current.

E. **__Buffers__** are substances that resist a change in pH when an acid or base is added to the solution. They are generally formed by mixing a weak acid or base is added to the solution. They are generally formed by mixing a weak acid and weak base. If a strong acid is added to the mixture, the weak base bonds to the hydrogen ions to neutralize the acid; if a strong base is added to the mixture, the weak acid releases hydrogen ions to neutralize the base. In either case, the pH does not change significantly.

Buffers can only work for so long, then the pH will shift rapidly.

12. Give the approximate pH of each of the following solutions then identify each as an acid (A) [pH of 1-6], base (B) [pH of 8-14) or essentially neutral (N) [pH of 6-8].

1. Tomato Juice **__Acidic 4.__** 2. Human Blood **__Basic 8.__** 3. Vinegar **__Acidic 2.__** 4. Pure Water **__Neutral 7.__** 5. Coffee **__Acidic 5.__** 6. Ammonia **__Basic 11.__** 7. Seawater **__Basic 8.__** 8. Typical Rainwater **__Acidic 5.__** 9. Oven/Drain Cleaner **__Basic 14.__** 10. Antacid Pills (tums) **__Basic 9__** 11. Urine **__Acidic 5__** 12. Gastric Juice **__Acidic 1.__**

13. Complete the following matching

1. **__N__** acid stomach 2. **__K__** acids 3. __**F**__ pH scale 4. **__J__** chemical burns 5. **__H__** H+ 6. **__D__** bases 7. **__I__** examples of basic solutions 8. **__A__** coma 9. **__B__** Respiratory Acidosis 10. **__C__** OH- 11. **__M__** tetany 12. **__L__** examples of acid solutions 13. **__E__** alkolosis 14. **__G__** buffer system

14. a) If a sulfur atom has six electrons in its outer shell of electrons, how many covalent bonds is it likely to form with outer atoms? Why?
 * Two because it needs a total of 8 electrons in the outer shell to be stable.**

b) If a hydrogen atom has one electron in its outer shell of electrons, how many covalent bonds is it likely to form with other atoms? Why?
 * One because with a hydrogen atom it must have two in its outer shell to be stable.**

c) What do you think the chemical formula for hydrogen sulfide would be?
 * H1S1.**

15. In your own words, explain the main difference between a polar covalent bond and a nonpolar covalent bond.
 * Polar covalent bonds: does not share electrons equally; more negatively charged. Hydrophyllic. There is a difference in charge of atoms.**


 * Nonpolar Covalent Bonds: share electrons equally. Hydrophobic. No difference in charge of atoms.**

16. If a water molecule is neutral (has no net charge), then why does it attract molecules and repel nonpolar ones?
 * Because polar covalent bonds are hydrophyllic.**

17. Explain why sweating helps cool the body when it is overheated?
 * Through evaporative cooling. As the sweat if evaporated, energy is absorbed from the skin.**

//Sample test questions for chapter 2 and lab #6:// 1. A substance that cannot be broken down into simpler substances by ordinary chemical means is known as a(n) a. molecule b. ion c. element e. isotope
 * d. compound**

2. A sulfur atom has 6 electrons in its outer energy shell. As a result, it tends to form _ covalent bonds with other atoms. b. 3 c. 4 d. 6 e. 8
 * a. 2**

3. A phosphorus atom has an atomic mass (mass number) of 31 and an atomic number of 15. How many PROTONS are there in a neutral phosphorus atom? b. 16 c. 31 d. 46 e. none of the above
 * a. 15**

4. A __is a substance particle that carries a__  charge a. proton.....negative c. neutron.....negative d. proton......neutral e. electron.....neutral
 * b. electron.....negative**

5. Isotopes of an element differ in their number of: a. electrons b. bonds formed by atom d. neutrons e. nuclei
 * c. protons**

6. When hydrogen atoms lose one electron to become an ion, their net electrical charge is b. -1 c. remains neutral d. impossible to know from just this information provided
 * a. +1**

7. A solution at pH of 4 contains the concentration of hydrogen ions as the same amount of a solution with a pH of 2. b. 2 times less c. 30 times more d. 20 times less e. 100 times less
 * a. 2 times more**

8. This property of water makes it possible for columns of liquid water to rise from roots to leaves insidenarrow pipelines of vascular tissues inside a plant b. temperature c. water sickness d. surface tension e. none of the above
 * a. cohesion**

9. Bonds that form when atoms transfer one or more electrons are called __ bonds a. ionic b. polar covalent c. hydrogen
 * d. non-polar covalent**