Chemistry Homework #11

Oil and water

cooking oil

Water

Pg 83-84 # 20-27, 33, 35

20. Using Figure 1.44 on page 70, decide which is more acidic:

a.     A soft drink or a tomato: Soft drink

b.     Black coffee or pure water: Black coffee

c.      Milk of magnesia or household ammonia: Milk of magnesia

21. How many times more acidic is a solution at pH 2.0 than a solution at pH 4.0?

a.     pH 4.0 is 20 times more acidic than pH 4.0.

22. List three negative effects of inappropriate pH levels on aquatic organisms.

a.     HIGH ACIDITY: fish-egg development is impaired, thus hampering the ability of fish to reproduce.

b.     ACIDIC: increased concentration of metal ions in natural waters by leaching metal ions from surrounding soil.

c.      BASIC CONTAMINATION: alkaline solutions are able to dissolve organic materials, including skin and scales.

23. Distinguish between polar and nonpolar molecules.

a.     POLAR: Water molecules are polar. Water is a common example of a polar solvent. Such charge separation (and resulting molecular polarity) is found in many molecules whose atoms have sufficiently different electronegativities. Polar molecules tend to dissolve readily in polar solvents, such as water.

b.     NONPOLAR: Nonpolar molecules (such as those of oil and gasoline) do not dissolve well in polar solvents (such as water or ethanol). Also, they readily dissolve nonpolar molecules.

24. Would you select ethanol, water, or lamp oil to dissolve a nonpolar molecular substance? Explain.

a.     I would select lamp oil to dissolve a nonpolar molecular substance because nonpolar substances dissolve in nonpolar solvents and different types of oil are nonpolar solvents.

25. Why does table salt (NaCl) dissolve in water but not in cooking oil?

a.     Table salt dissolves in water but not in cooking oil because table salt is a polar substance, similar to water, which helps to dissolve the substance while in oil, the polarity of the salt would not dissolve in the nonpolarity of oil.

26. Explain the phrase “like dissolves like”.

a.     This phrase means the pattern of solubility. The pattern of solubility is that polar substances dissolve in polar solvents, and nonpolar substances dissolve in nonpolar solvents.

27. Explain why you cannot satisfactorily clean greasy dishes with just plain water.

a.     You cannot satisfactorily clean greasy dishes with just plain water because a nonpolar solvent cannot dissolve a polar substance.

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.

                                               i.     Materials likely to be found in those cleaners are nonpolar substances.

b.     Why using these cleaners is more effective than washing with water.

                                               i.     Using those cleaners is more effective than washing with water due to the polar nature of water.

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.

a.     I would expect the Hydrogen atom to have a partial positive charge because Hydrogen as an ion has a positive charge, and never negative, similar to how Fluorine always has a negative ion charge.