Chemistry 1A Fall 2010 Exam 1 Key Chapters 1-3 and part 4

Transcription

1 Chemistry 1A Fall 2010 Exam 1 Key Chapters 1-3 and part YOU MIGHT FIND THE FOLLOWING USEFUL; Electronegativities H 2.2 Li Be B C N O F Na Mg Al Si P S Cl K Ca Ga Ge As Se Br Rb Sr In Sn Sb Te I Xe Cs Ba Tl Pb Bi Po Substance Density in g/ml battery acid 1.29 benzene, C 6H blood (whole) 1.05 bromine, Br chocolate 1.75 copper, Cu 8.9 chromium(iii) oxide, Cr 2O gasoline gold, Au 19.0 Iron, Fe 7.87 magnesium, Mg 1.7 nitrobenzene, C 6H 5NO oleic acid sea water sodium chloride, NaCl 2.16 sulfuric acid (concentrated) 1.8 water at 20 C

2 Answer the following by writing the word, words, letter, letters or number in each blank that best completes each sentence. (1½ point each blank) 1. Substances that are capable of being extended or shaped by the blows of a hammer are malleable. 2. Allotropes are different forms of an element in the same physical state at the same temperature and pressure. 3. The elements in group 1 on the periodic table are called alkali metals.. Precision describes the closeness in value of a series of measurements of the same entity. Accuracy describes how closely a measured value approaches the true value of a property. 5. Organic chemistry is the branch of chemistry that involves the study of carbon-based compounds. 6. A(n) oxyanion is a polyatomic ions with the general formula HaXbOc d. (The a can be 0.) 7. A(n) dipole is a molecule that contains an asymmetrical distribution of positive and negative charges. 8. Isomers are compounds that have the same molecular formula but different molecular structures. 9. A(n) formula unit is a group represented by a substance s chemical formula, that is, a group containing the kinds and numbers of atoms or ions listed in the chemical formula. It is a general term that can be used in reference to elements, molecular compounds, or ionic compounds. 10. Selenium, Se, is a solid (solid, liquid, or gas) at room temperature and pressure. 11. The P-F bond is polar covalent (nonpolar covalent, polar covalent, or ionic). 12. In the N-H bond the nitrogen atom has a partial negative charge. 13. Draw a reasonable Lewis structure for CH 3COF. ( points) 2

3 1. Identify each of the following as a binary covalent compound, a binary ionic compound, a binary acid, an ionic compound with a polyatomic ion, an oxyacid, an alcohol, or a sugar. Write name for each. (8 points) Chemical Formula Type of Substance Name S 2F 10 binary covalent disulfur decafluoride Cu(H 2PO ) 2 ionic with polyatomic ion copper(ii) dihydrogen phosphate C 5H 12 binary covalent (hydrocarbon) pentane H 2SO 3 oxyacid sulfurous acid 15. Identify each of the following as a binary covalent compound, a binary ionic compound, a binary acid, an ionic compound with a polyatomic ion, an oxyacid, an alcohol, or a sugar. Write formula for each.) (8 points) Chemical Formula Type of Substance Formula hydrogen sulfide binary covalent H 2S glucose sugar C 6H 12O 6 cadmium nitrite ionic with polyatomic ion Cd(NO 2) 2 hydrofluoric acid binary acid HF(aq) 16. The name that corresponds to the following structure is 3-ethylheptane. (3 points) 17. When the solid amino acid methionine, C 5H 11NSO 2, reacts with oxygen gas, the products are carbon dioxide gas, liquid water, sulfur dioxide gas, and nitrogen gas. Write a complete, balanced equation for this reaction. (6 points) 2C 5H 11NSO 2(s) + 31/2O 2(g) 10CO 2(g) + 11H 2O(l) + 2SO 2(g) + N 2(g) or C 5H 11NSO 2(s) + 31O 2(g) 20CO 2(g) + 22H 2O(l) + SO 2(g) + 2N 2(g) 3

4 18. Complete the following table by (1) writing the name for the type of particle viewed as forming the basic structure of each of the following substances and (2) writing the name of the type of attraction holding these particles in the solid and liquid form, e.g. covalent bonds, dipole-dipole attractions, etc. (1 point each box) Substance Particles to Visualize Type of Attraction sulfur molecules London forces C 6H 13OH molecules hydrogen bonds and London forces krypton atoms London forces CrF 3 Cr 3+ cations and F anions ionic bonds chromium cations in a sea of electrons metallic bonds C 7H 16 molecules London forces hydrogen chloride molecules dipole-dipole attractions and London forces NH OH NH + cations and OH anions ionic bonds

5 For the following numerical problems, be sure to carefully show your work and round your answer using the appropriate guidelines. NOTE: Remember that there is part credit for each problem. Even if you cannot do all of a problem, be sure to set up as much of it as you can. 19. Chocolate contains theobromine, which is a smooth muscle stimulant that is similar to caffeine. How many pounds of chocolate that is 1.7% theobromine would you have to eat to consume mg of theobromine? (7 points) 100 mg chocolate 1 g 1 lb = 0.11 lb chocolate? lb chocolate = mg theobromine 1.7 mg theobromine 10 3 mg 53.6 g 20. Scandium metal, Sc, is made from scandium oxide, Sc 2O 3. What is the maximum mass, in kilograms, of scandium metal, Sc, that can be made from kilograms of Sc 2O 3? (7 points) 3 10 g 1 mol Sc 2O3 2 mol Sc.9559 g Sc 1 kg? kg Sc = kg Sc2O3 3 = 7.67 kg Sc 1 kg g Sc 2 O 3 1 mol Sc 2 O 3 1 mol Sc 10 g 21. Potassium permanganate, KMnO, a common oxidizing agent, is made from various ores that contain manganese(iv) oxide, MnO 2. The following equation shows the net reaction for one process that forms potassium permanganate. 2MnO 2 + 2KOH + O 2 2KMnO + H 2 a. What is the maximum mass, in kilograms, of KMnO that can be made from the reaction of g of MnO 2 with 585 g of KOH and excess oxygen gas? (7 points) 2 x g KMnO 1 kg? kg KMnO = g MnO2 3 = kg KMnO 2 x g MnO2 10 g g KMnO 1 kg? kg KMnO = 585 g KOH 3 = 1.65 kg KMnO g KOH 10 g b. Explain why the oxygen gas is in excess. ( points) Because air contains oxygen gas, the oxygen is less expensive than the other reactants. It s especially important that the manganese reactant is used most efficiently, so it is limiting. Oxygen is very safe, so we don t mind having some left over. Because the O 2 is a gas, it is easily separated from the solid product, KMnO. 5

6 Answer the following in short answer form. 22. Write a description of the element iodine as it is found at room temperatures and pressures. Your description should include mention of the particles that form its structure, whether it s a gas, liquid, or solid, how the particles are moving, how much space they occupy, and the strengths of attractions between the particles. Iodine is composed of diatomic molecules, I 2, with 53 protons and a +53 charge in each of the two nuclei surrounded by a 106 electron -charge cloud. Iodine is a solid at room temperature and pressure so the particles occupy about 70% of the volume of the solid. Although they are moving constantly, the attractions between particles are strong enough to keep each particle trapped in a cage. The particles are colliding with other particles many times per second, leading to continuous changes in direction and velocity. 23. Describe the London dispersion forces that can arise between iodine molecules. Your description should include mention of how the attractions form beginning with nonpolar iodine molecules. 6