20) Using Figure 1.44 on page 70, decide which is more acidic:
a. a soft drink or a tomato
b. black coffee or pure water
c. milk of magnesia or household ammonia
a. a tomato.
b. pure water.
c. milk of magnesia.
21) How many times more acidic is a solution at pH 2.0 than a solution at pH 4.0.
Since there is a tenfold difference between each number on the pH scale, a solution at pH 4.0 is 100 times more acidic than a solution at pH 2.0.
22) List three negative effects of inappropriate pH levels on aquatic organisms.
Too low pH (high acidity):
1) fish egg development impaired, reproduction harmed.
2) increased concentrations of metal ions in natural waters by leaching metal ions from surrounding soil.
High pH (basic contamination):
3) dissolves organic materials, such as scales on fish.
23) Distinguish between polar and nonpolar molecules.
A polar molecule is a molecule with an uneven distribution of electrical charge; each molecule has a partial positive region at one end and a partial negative region at the other end. H2O (water) is a polar molecule, since there 8 oxygen electrons and only 2 hydrogen electrons. Since there are more electrons in oxygen, there is a greater negative charge at the oxygen end, and a partially positive charge at the hydrogen end of the molecule. A nonpolar molecule's distribution of electrical charge is equal throughout, meaning it is balanced at both ends of the molecule.
24) Would you select ethanol, water, or lamp oil to dissolve a nonpolar substance? Explain.
Ethanol and water are both polar substances, so, to dissolve a nonpolar substance, I would select the nonpolar substance, lamp oil; polar substances dissolve in polar solvents and nonpolar substances dissolve in nonpolar solvents-- "like dissolves like."
25) Why does table salt (NaCl) dissolve in water but not cooking oil?
Since water is an extremely attractive polar molecule, the positive and negative charges of Na (cation) Cl (anion) are "pulled" by the charges of the water molecules. Cooking oil on the other hand, is nonpolar; therefore, cooking oil does not have the same effect on NaCl as water does, and NaCl does not dissolve in it.
26) Explain the phrase "like dissolves like."
As I stated in #24, polar substances dissolve in polar solvents and nonpolar substances dissolve in nonpolar solvents. This relationship between solvents that dissolve solutes with similar electrical charges is described as "like dissolves like."
27) Explain why you cannot satisfactorily clean greasy dishes with just plain water.
Since water is composed of polar molecules and grease, or oil, is composed of nonpolar molecules, water would not be able to dissolve the grease on the dishes. In order to dissolve the grease, the dishes would need to be washed with a solution composed of nonpolar molecules. "Like dissolves like!"
33) Many mechanics prefer to use waterless hand cleaners to clean their greasy hands. Explain
a. what kind of materials are likely to be found in these cleaners.
b. why using these cleaners is more effective than washing with water.
a. Nonpolar materials are likely to be found in these cleaners.
b. Using these cleaners would be more effective than washing with water because since water molecules are polar, they would not dissolve the grease off of the mechanics' hands. Instead, the water would sort of roll off of their hands without them being cleaned.
35) Fluorine has the highest electronegativity of any element. Fluorine and hydrogen form a polar bond. Which atom in HF would you expect to have a partial positive charge? Explain.
Since fluorine (F) has the highest electronegativity of any element, meaning the most electrons, it would make up the negative end of the polar bond, HF. Since hydrogen (H) has less negative charges, or less electrons, than fluorine, it would have the partial positive charge of the polar bond.
Riverwood Fish Kill!
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