HON 225 October 1, 2014 Please print Quiz #3: 50 pts 1. (11 pts) Balance the following chemical equations: a. P4 + 10 Cl2 = 4 PCl5 b. C4H8O2 + 5 O2 = 4 CO2 + 4 H2O c. 2 H2S + 3 O2 = 2 SO2 + 2 H2O 2. (1 pt each) Answer the following true or false questions. Please print clearly. a. F The solubility of a solid solute will typically increase as temperature decreases. b. F A salt solution which contains less than the maximum amount of dissolved solute that it is capable of holding is said to be saturated. c. T Atoms, ions, and molecules may all occupy lattice positions in a crystalline solid. d. F A crystalline solid contains aggregates of large numbers of randomly-arranged small crystals. e. F A stable octet consists of 8 horses singing in a barn. f. F The halogens and noble (inert) gases are the most metallic elements on the periodic table. 3. (1 pt each) Predict the stable, neutral binary compounds formed from the following. In other words, what is the ratio between these elements in a neutral compound? a. Li and F LiF b. Mg and O MgO c. H and S H2S4. (3 pts each) Using the appropriate number of electron "shells", draw the electronic structure of the following atoms. Indicate the number of valence electrons in each. a. Be (atomic number = 4) 2 valence electrons b. S (atomic number = 16) 6 valence electrons 5. (2 pts each) Give one example each of a gaseous solution and a solid solution. Gaseous solution: Air Solid solution: Metal alloy such as bronze or brass BeS6. (5 pts) State an example of human-caused water pollution. Describe how the pollutant affects life forms in or near the water. Hg: metabolized by bacteria in water to make a soluble form of Hg, which gets into fish. People eat fish and develop Hg poisoning (neurological problems, known as “Mad Hatter’s Disease”). Fertilizer: runoff containing fertilizer enters pond or lake, feeds algae, which bloom. Algae growth consumes oxygen in water, killing fish. Bacteria which consume fish utilize S instead of O (since no O in water), producing foul-smelling H2S products. Heat: water is warmed by power plants and returned to the river, where the higher temperature results in lower oxygen solubility, killing fish and leading also to algae blooms which utilize S instead of O (since no O in water), producing foul-smelling H2S products. 7. (4 pts) Why is water such a good solvent for salts (i.e., how does water dissolve the ions that comprise salt)? A sketch showing how water dissolves salts might help. Water has a charge separation within the molecule, allowing it to surround and dissolve ions in solution. Each positive ion, for example, attracts the negative end of surrounding water molecules which form a shell around it, keeping it dissolved. 8. (2 pts each) Match the solid with its definition. a. 2 Crystalline solid 1. Has no microscopic structure b. 3 Polycrystalline solid 2. Has regular, repeating structural units c. 1 Amorphous solid 3. Has many microscopic crystals 9. (5 pts) Glass and quartz are similar in chemical composition, containing mainly Si and O in a 1:2 ratio. Glass is an amorphous solid while quartz is a crystalline solid. Describe the differences you would expect in their microscopic structures and melting temperature ranges. Quartz is crystalline and forms slowly, so its structure is an organized lattice or 3-D array of alternating Si and O atoms. The Si and O have time to find the energetically most favorable position as the crystal grows. The melting temperature is a broad range, since bonds are of different lengths. Glass is a super or instantly-cooled liquid. All the disorder between Si and O atoms that would be found in a liquid are preserved because the glass solidifies instantaneously from the liquid phase – there is no microscopic structure, just preserved disorder. The melting temperature range is very narrow, since all of the bonds are the same