Chemistry Name: ANSWER KEY Materials & Resources sections C and D reading guide Date: Period: Section C.1 (pp. 128-131) 1. Explain how the Law of Conservation of Matter applies to chemical reactions. Matter is neither created or destroyed. To apply this law to a chemical reaction, you must add coefficients to balance the reaction. This way, the number of atoms of each element are the same among the reactants and products. 2. When an equation is balanced it means that the number of atoms of each element are the same among the reactants and products. 3. Define formula unit: the smallest particle found in an ionic compound sample. 4. Define molecule: the smallest particle found in a covalent compound sample (or a diatomic molecule). 5. Complete Building Skills 6, ONLY questions 2 and 3. Question 1 is completed as an example for you in the book.
Section C.2 (pp. 131-135) 1. Complete Building Skills 7, questions 2 through 6. You don t have to draw the pictures, just write the balanced equations. 2. 2 CuO + 1 C 2 Cu + 1 CO 2 3. 4 NH 3 + 7 O 2 4 NO 2 + 6 H 2 O 4. 2 O 3 3 O 2 5. 1 Cu + 2 AgNO 3 1 Cu(NO 3 ) 2 + 2 Ag 6. 2 C 8 H 18 + 25 O 2 16 CO 2 + 18 H 2 O 2. List the seven diatomic molecules. H O N Cl Br I F. Section C.3 (pp. 135-137) 1. A mole of particles means how many particles? 6.02 x 10 23 particles.
2. Molar masses are found on the periodic table. What does one mole of carbon atoms weigh? 12.0 g. What does one mole of sodium atoms weigh? 23.0 g What does one mole of CaCl 2 weigh? 111.1 g 3. How many hydrogen atoms are in the formula (NH 4 ) 3 PO 4? 12. 4. Complete Building Skills 8. Write your answers below. 1. 14.0 g/mol 4. 342.0 g/mol 2. 28.0 g/mol 5. 183.6 g/mol 3. 58.5 g/mol 6. 344.5 g/mol 5. Complete the following mole conversions. Show the dimensional analysis work. Refer to class notes and mole cards to help you. a. 28.5 g Cu is how many moles? 28.5 g Cu x 1 mol Cu = 0.45 mol Cu 63.5 g Cu b. 1.08 x 10 24 molecules H 2 O is how many moles? 1.08 x 10 24 molecules H 2 O x 1 mol H 2 O 6.02 x 10 23 molecules H 2 O = 1.8 mol H 2O Section C.4 (pp. 140-142) 1. Define percent composition. The percent by mass of each element found in a chemical compound. Use molar masses to calculate.
2. Elements are found in minerals, and minerals are found in ores. For example, Cu is found in the mineral chalcocite (Cu 2 S), and chalcocite is only a small part of a larger rock called an ore. Let s say a 500 gram ore is found. This ore is 30% chalcocite. How many grams of Cu can be extracted from the ore? Show your math work. 500 g ore x 30% = 150 g chalcocite available % Cu in chalcocite = 127.0 g Cu = 80 % Cu 159 g Cu 2 S 150 g mineral x 80% Cu = 120 g Cu available in the ore. Section C.6 (pp. 145-147) 1. Define renewable resources. A resource that is renewed by natural processes in a reasonable amount of time. 2. Petroleum is a nonrenewable resource because it takes millions of years for natural processes to renew petroleum. This is not a reasonable amount of time. 3. Each person in the United States throws away about 2 kg (4 lb) of waste daily. This trash ends up in landfills and may or may not decompose. 4. The largest fraction of municipal waste in the US is paper. According to the bottom pie chart on p.147, yard waste and food waste contribute 10.4 and 13.6 percent respectively. 5. Speaking of yard waste and food waste, perhaps you know what composting is. If not, perform an internet search. Explain how setting up a compost pile at home can reduce the amount of waste humans deposit into landfills each day. Composting is when soil organisms and microorganisms decompose waste materials, producing humus. Humus contains many (or all) of the necessary nutrients for plant growth. Instead of throwing away kitchen food scraps and yard wastes, you can create a compost pile in your yard to produce free, natural fertilizer (humus) for your garden. Also, humus improves the structure of the soil something a synthetic fertilizer cannot do! A well-structured soil has lots of pore space trapped air in-between the dirt that makes the soil fluffy and easy for the plant to send roots through. Section D.1 (pp. 153-155) 1. Answer the question presented in ChemQuandry 2. The element being described is carbon. The reason the materials have different properties is due to the way the carbon atoms are bonded to each other in each sample. We would need to examine the internal structure the atom packing that is going on in each sample to explain the different properties observed.
2. Define allotropes: Allotropes are samples of a single element that have different physical structures, and therefore different chemical and physical properties. 3. Research two allotropes of oxygen. Give their names, formulas, and some physical properties. Oxygen gas, O 2, and ozone gas, O 3. Oxygen is a colorless gas, while Ozone is a pale blue gas at ambient conditions. Ground-level ozone is classified as an air pollutant. Section D.2 (pp. 156-158) 1. Pencil lead can be hard or soft, and each type of pencil lead has its advantages. What material is mixed with the graphite in the lead to make it harder? Clay 2. The underside of the space shuttle is covered with many small, ceramic tiles. What spaceflight problem do these tiles solve? These tiles absorb the tremendous amount of heat generated during re-entry. 3. Some of these tiles were damaged during the January 2003 launch of the spacecraft Columbia. How were they damaged, and what was the ultimate tragic result of their damage? A piece of foam insulation broke off of the shuttle and hit the tile, damaging it. When the space shuttle re-entered Earth s atmosphere, this damaged tile allowed tremendous heat buildup on the wing of the space shuttle, and the shuttle blew up. Section D.4 (pp. 160-162) 1. Define alloy: A solid combination of two or more metals. It is a solid homogeneous mixture. 2. Identify the primary metal in each alloy: a. yellow brass: copper b. steel: iron c. pewter: tin d. bronze (use an Internet source) copper e. what is the % of gold in an 18-carat gold ring? (use an Internet source) 75%
Complete Section C Summary Questions 3, 4, 7 through 9, 12, and 17 on the back of this page. 3. Using up and throwing away are inaccurate terms because atoms can never disappear during a chemical reaction. 4. a) 32.0 g/mol b) 48.0 g/mol c) 194.0 g/mol d) 58.3 g/mol e) 180.0 g/mol 7. a) Na = 2 S = 1 O = 4 K = 2 Cl = 1 reactants Na = 2 S = 1 O = 4 K = 2 Cl = 1 products b) The equation is NOT properly balanced. You cannot change the subscripts. c) 1 Na 2 SO 4 + 2 KCl 2 NaCl + K 2 SO 4 8. a) 87% Ag b) 53% Al c) 40% Ca 9. a) 68% b) 10% c) 3.4 g Pb in the ore 12. a) reusing b) recycling c) reusing 17. It is very costly to extract Al metal from ores a large amount of electricity is needed for the process. Aluminum in cans has already been extracted from the ore, and only needs to be melted and re-cast into a new shape. This requires much less energy.