Assignment:
Part 1
Choose the BEST answer to each of the following.
1. Someone argues that he or she doesn't drink tap water because it contains thousands of molecules of some impurity in each glass. How would you respond in defense of the water's purity, if it indeed does contain thousands of molecules of some impurity per glass?
(a) Impurities aren't necessarily bad; in fact, they may be good for you.
(b) The water contains water molecules, and each water molecule is pure.
(c) There's no defense. If the water contains impurities, it should not be drunk.
(d) Compared to the billions and billions of water molecules, a thousand molecules of something else is practically nothing.
2. What is the difference between a compound and a mixture?
(a) Both consist of atoms of different elements.
(b) Their atoms are bonded together in different ways.
(c) The components of a mixture are not chemically bonded together.
(d) One is a solid and the other is a liquid.
3. The air in your house is an example of a
(a) homogeneous mixture because it is mixed very well.
(b) heterogeneous mixture because of the dust particles it contains.
(c) homogeneous mixture because it is all at the same temperature.
(d) heterogeneous mixture because it consists of different types of molecules.
4. Half-frozen fruit punch is always sweeter than the same fruit punch completely melted because
(a) the sugar sinks to the bottom.
(b) only the water freezes while the sugar remains in solution.
(c) the half-frozen fruit punch is warmer.
(d) sugar molecules solidify as crystals.
5. Why is sodium chloride, NaCl, insoluble in gasoline? Consider the electrical attractions.
(a) Because this molecule is so small, there is not much opportunity for the gasoline to interact with it through any electrical attractions.
(b) Because gasoline is a very polar molecule, the salt can form only dipole-induced dipole bonds, which are very weak, giving it a low solubility in gasoline.
(c) Because gasoline is so strongly attracted to itself, the salt, NaCl, is excluded.
(d) Salt is composed of ions that are too attracted to themselves. Gasoline is nonpolar, so salt and gasoline will not interact very well.
6. Fish don't live very long in water that has just been boiled and brought back to room temperature. Why?
(a) There is now a higher concentration of dissolved CO2 in the water.
(b) The nutrients in the water have been destroyed.
(c) Since some of the water evaporated while boiling, the salts in the water are now more concentrated. This has a negative effect on the fish.
(d) The boiling process removes the air that was dissolved in the water. Upon cooling, the water does not have its usual air content-hence, the fish drown.
7. How many moles of sugar (sucrose) are there in 5 L of sugar water that has a concentration of 0.5 M?
(a) 5.5 moles
(b) 5.0 moles
(c) 2.5 moles
(d) 1.5 moles
8. What is an advantage of using chlorine gas to disinfect drinking water supplies?
(a) It provides residual protection against pathogens.
(b) It gives the water a fresh taste.
(c) Residual chlorine in water helps to whiten teeth.
(d) Excess chlorine is absorbed in our bodies as a mineral supplement.
(e) All of the above.
9. Why do red blood cells, which contain an aqueous solution of dissolved ions and minerals, burst when placed in fresh water?
(a) The dissolved ions provide a pressure that eventually bursts open the cell.
(b) More water molecules enter the cell than leave the cell.
(c) The fresh water acts to dissolve the blood cell wall.
(d) All of the above.
10. A stagnant pond smells worse than a babbling brook because
(a) odors are not transported downstream.
(b) of the type of aquatic life it attracts.
(c) it lacks sufficient dissolved oxygen.
(d) All of the above.
Part 2
Choose the BEST answer to each of the following.
1. What coefficients balance this equation? ____P4(s) + ____H2(g)h____PH3(g)
(a) 4, 2, 3
(b) 1, 6, 4
(c) 1, 4, 4
(d) 2, 10, 8
2. What is the formula mass of sulfur dioxide, SO2?
(a) about 16 amu
(b) about 32 amu
(c) about 60 amu
(d) about 64 amu
3. Which has the greatest number of atoms?
(a) 28 g of nitrogen, N2
(b) 32 g of oxygen, O2
(c) 16 g of methane, CH4
(d) 38 g of fluorine, F2
4. How many molecules of aspirin (formula mass = 180 amu) are there in a 0.250-g sample?
(a) 6.02 * 1023
(b) 8.38 * 1020
(c) 1.51 * 1023
(d) More information is needed.
5. The yeast in bread dough feeds on sugar to produce carbon dioxide. Why does the dough rise faster in a warmer area?
(a) There is a greater number of effective collisions among reacting molecules.
(b) Atmospheric pressure decreases with increasing temperature.
(c) The yeast tends to "wake up" with warmer temperatures, which is why baker's yeast is best stored in the refrigerator.
(d) The rate of evaporation increases with increasing temperature.
6. What can you deduce about the activation energy of a reaction that takes billions of years to go to completion. How about a reaction that takes only fractions of a second?
(a) The activation energy of both these reactions must be very low.
(b) The activation energy of both these reactions must be very high.
(c) The slow reaction must have a high activation energy, while the fast reaction must have a low activation energy.
(d) The slow reaction must have a low activation energy, while the fast reaction must have a high activation energy.
7. What role do CFCs play in the catalytic destruction of ozone?
(a) Ozone is destroyed upon binding to a CFC molecule that has been energized by ultraviolet light.
(b) There is no strong scientific evidence that CFCs play a significant role in the catalytic destruction of ozone.
(c) CFC molecules activate chlorine atoms into their catalytic action.
(d) CFC molecules migrate to the upper stratosphere where they generate chlorine atoms upon being destroyed by ultraviolet light.
8. Is the synthesis of ozone, O3, from oxygen, O2, an example of an exothermic or endothermic reaction? Why?
(a) exothermic, because ultraviolet light is emitted during its formation
(b) endothermic, because ultraviolet light is emitted during its formation
(c) exothermic, because ultraviolet light is absorbed during its formation
(d) endothermic, because ultraviolet light is absorbed during its formation
9. How much energy, in kilojoules, is released or absorbed from the reaction of 1 mole of nitrogen, N2, with 3 moles of molecular hydrogen, H2, to form 2 moles of ammonia, NH3? Consult Table 17.1 for bond energies.
(a) +899 kJ/mol
(b) -993 kJ/mol
(c) +80 kJ/mol
(d) -80 kJ/mol
10. How is it possible to cause an endothermic reaction to proceed when the reaction causes energy to become less dispersed?
(a) The reaction should be placed in a vacuum.
(b) The reaction should be cooled down.
(c) The concentration of the reactants should be increased.
(d) The reaction should be heated.