Download AP Chem – Unit 1 Part 2 AP Chemistry 2016-‐2017 Unit 1

AP Chem – Unit 1 Part 2 AP Chemistry 2016-­‐2017 Unit 1: Measurement, Matter, and Stoichiometry (Ch. 1-­‐3) After completion of unit 1 I will be able to… • Identify an element or determine its purity using mass percent calculations. • Use mole relationships to convert between moles, mass and particles. • Balance chemical reactions and use mole ratios to predict amounts needed or produced in a chemical reaction. • Identify different properties of solids and liquids based on both differences in structure at both a particle and macro level. • Identify and name ionic compounds. • Identify and name molecular compounds. • Calculate a reactions percent yield taking into account limiting and excess reactants. • Determine the empirical formula of a substance from lab data. • Classify a reaction as a chemical, physical or ambiguous change. • Identify the difference between a chemical and physical change based on inter and intra molecular forces. *Note the above list is not an exhaustive list. Ch. 3 Stoichiometry Warm-­‐up: Balance the following equations. (a.) (NH4)2Cr2O7(s) à Cr2O3(s) + N2(g) + H2O(g) (b.) NH3(g) + O2(g) à NO(g) + H2O(g) [A: 1,1,1,4] [A: 4,5,4,6] The Mole Mole Example Problem 1: Americium is an element that does not occur naturally. It can be made in very small amounts in a device known as a particle accelerator. Compute the mass in grams of a sample of americium containing six atoms. [2.42 x 10-­‐21 g] AP Chem – Unit 1 Part 2 Example Problem 2: A silicon chip used in an integrated circuit of a microcomputer has a mass of 5.68 mg. How many silicon atoms are present in the chip? [1.22 x 1020 atoms] Molar Mass (Formula Weight) Example Problem 3: Juglone, a dye known for centuries, is produced from the husks of black walnuts. It is also a natural herbicide that kills off competitive plants around the black walnut tree but does not affect grass and other noncompetitive plants. The formula for juglone is C10H6O3. (a.) Calculate the molar mass of juglone. [174.1g/mol] (b.) A sample of 1.56 x 10-­‐2 g of pure juglone was extracted from black walnut husks. How many moles of juglone does this sample represent? [8.96 x 10-­‐5 mol] Example Problem 4: Calcium carbonate, also called calcite, is the principle mineral found in limestone, marble, chalk, pearls, and the shells of marine animals such as clams. (a) Calculate the molar mass of calcium carbonate. [100.09 g/mol] (b) A certain sample of calcium carbonate contains 4.86 moles. What is the mass in grams of this sample? What is the mass of the CO32-­‐ ions present? [486 g CaCO3; 292 g CO32-­‐] Example Problem 5: A silicon chip used in an integrated circuit of a microcomputer has a mass of 5.68 mg. How many silicon atoms are present in the chip? [1.22 x 1020 atoms] Example Problem 6: Isopentyl acetate is the compound responsible for the scent of bananas. The formula for isopentyl acetate is C7H14O2. Interestingly, bees release about 1 µg of this compound when they sting. The resulting scent attracts other bees to join the attack. How many molecules of isopentyl acetate are released in a typical bee sting? How many atoms of carbon are present? [5 x 1015 molecules; 4 x 1016 carbon atoms] AP Chem – Unit 1 Part 2 Percent Composition of Compounds Example Problem 7: Calculate the mass percent of ethanol, C2H5OH. [52.14% C; 13.13% H; 34.73% O] Example Problem 8: Carvone is a substance that occurs in two forms having different arrangements of the atoms but the same molecular formula (C10H14O) and mass. One type of carvone gives caraway seeds their characteristic smell, and the other type is responsible for the smell of spearmint oil. Compute the mass percent of each element in carvone. [79.94% C; 9.41% H; 10.65% O] Example Problem 9: Penicillin, the first of a now large number of antibiotics, was discovered accidentally by the Scottish bacteriologist Alexander Fleming in 1928, but he was never able to isolate it as a pure compound. This and similar antibiotics have saved millions of lives that might have been lost to infections. Penicillin F has the formula C14H20N2SO4. Compute the mass percent of each element. [53.82% C; 6.466% H; 8.969% N; 10.27% S; 20.49% O] Empirical and Molecular Formulas AP Chem – Unit 1 Part 2 Empirical Formula Molecular Formula Hydrates Anhydrous Example Problem 10: Determine the empirical and molecular formulas for a compound that is given the following analysis (in mass percents): 71.65% Cl; 24.27% C; 4.07% H. The molar mass is known to be 98.96 g/mol. [empirical formula = CH2Cl; molecular formula = C2H4Cl2] Example Problem 11: The compound para-­‐aminobenzoic acid (you may have seen it listed as PABA on your bottle of sunscreen) is composed of carbon (61.31%), hydrogen (5.14%), nitrogen (10.21%), and oxygen (23.33%). Find the empirical formula of PABA. [C7H7NO2] Example Problem 12: A white powder is analyzed and found to contain 43.64% phosphorus and 56.36% oxygen by mass. What is the compound’s empirical formula? The compound has a molar mass of 283.88 g/mol. What is the molecular formula? [Empirical formula = P2O5; molecular formula P4O10] AP Chem – Unit 1 Part 2 Example Problem 13: Caffeine contains 49.48% C, 5.15% H, 28.87% N, and 16.49% O. Determine the compound’s empirical formula. The compound has a molar mass of 194.2 g/mol. What is the molecular formula of caffeine? [empirical formula = C4H5N2O; molecular formula = C8H10N4O2] Combustion Analysis -­‐ POGIL Example Problem 14: A compound is composed of carbon, nitrogen, and hydrogen. When 0.1156 g of this compound is reacted with oxygen (burned, combusted), 0.1638 g of carbon dioxide and 0.1676 g of water are collected. What is the empirical formula of this compound? [CH5N] Example Problem 15: Capriotic acid, which is responsible for the foul odor of dirty socks, is composed of C, H, and O atoms. Combustion of a 0.225 g sample of this compound produces 0.512 g CO2 and 0.209 g H2O. (a.) What is the empirical formula of capriotic acid? [C3H6O] (b.) Capriotic acid has a molar mass of 116 g/mol. What is its molecular formula? [C6H12O2] AP Chem – Unit 1 Part 2 Example Problem 16: A compound contains only carbon, hydrogen, oxygen, and nitrogen. Combustion of 0.157 g of the compound produced 0.213 g of CO2, and 0.0310 g of H2O. In another experiment, 0.103 g of the compound produced 0.0230 g of NH3. What is the empirical formula of the compound? [C7H5N3O6] Example Problem 17: (Hydrates) Washing soda is a hydrate. Its formula can be written as Na2CO3·∙xH2O. When a 2.558-­‐g sample of washing soda is heated at 25°C, all the water of hydration is lost, leaving 0.948 g of Na2CO3. What is the value of x? [10; Na2CO3·∙10H2O] Stoichiometric Calculations Stoichiometry Example Problem 18: (A template for solving stoichiometry problems!!) (a) What mass of oxygen will react with 96.1 grams of propane? [349 g oxygen] (b) How many liters of carbon dioxide gas at STP (1 atm, 273K) would be formed? [146 L CO2] (c) How many water molecules are produced? [5.24 x 1024 molecules of water] AP Chem – Unit 1 Part 2 Example Problem 19: Solid lithium hydroxide is used in space vehicles to remove exhaled carbon dioxide from the living environment by forming solid lithium carbonate and liquid water. What mass of gaseous carbon dioxide can be absorbed by 1.00 kg of lithium hydroxide? [919 g CO2] Example Problem 20: Baking soda (sodium bicarbonate) is often used as an antacid. It neutralizes excess hydrochloric acid secreted by the stomach. Milk of magnesia, which is an aqueous suspension of magnesium hydroxide, is also used as an antacid to neutralize the hydrochloric acid secreted by the stomach. Which is the more effective antacid per gram, sodium bicarbonate or magnesium hydroxide? [Mg(OH)2] Calculations Involving a Limiting Reactant Example Problem 21: The Haber process (the AP Exam likes to ask questions about this…) is making ammonia for fertilizer production from the nitrogen in the air reacted with hydrogen gas. The hydrogen gas is obtained from the reaction of methane with water vapor. This process has saved millions from starvation. Suppose 25.0 kg of nitrogen reacts with 5.00 kg of hydrogen to form ammonia. What mass of ammonia can be produced? Which reactant is the limiting reactant? What is the mass of the reactant that is in excess? [23.1 kg ammonia; hydrogen is limiting reactant; 1.88 kg excess nitrogen] AP Chem – Unit 1 Part 2 Example Problem 22: Nitrogen gas can be prepared by passing gaseous ammonia over solid copper (II) oxide at high temperatures. The other products of the reaction are solid copper and water vapor. If a sample containing 18.1 g of ammonia is reacted with 90.4 g of copper (II) oxide, which is the limiting reactant? How many grams of nitrogen gas will be formed? How many grams of the excess reactant will be left over? [CuO is limiting; 10.6 g N2 formed; 5.2 g NH3 left over] Example Problem 23: Solutions of barium chloride and silver nitrate react to form solid silver chloride and a solution of barium nitrate. A solution containing 21.34 g of barium chloride is mixed with one containing 34.22 g of silver nitrate. How many grams of barium chloride, silver nitrate, silver chloride, and barium nitrate are present after the reaction is complete? [0.3748 g BaCl2; 0 g AgNO3; 28.86 g AgCl; 26.32 g Ba(NO3)2] AP Chem – Unit 1 Part 2 Percent Yield Theoretical Yield: Actual Yield: Percent Yield: Example Problem 24: Methanol (CH3OH), also called methyl alcohol, is the simplest alcohol. It is used as a fuel in race cars and is a potential replacement for gasoline. Methanol can be manufactured by combination of gaseous carbon monoxide and hydrogen. Suppose 68.5 kg CO(g) is reacted with 8.60 kg H2(g). Calculate the theoretical yield of methanol. If 3.57 x 104 g CH3OH is actually produced, what is the percent yield of methanol? [theoretical yield is 6.86 x 104 g; percent yield is 52.3%] End of the Chapter (after page 137) AP MC Review Questions (1-­‐17) – Solutions (PRACTICE THESE) 1. C, 2. B, 3. D, 4. C, 5. C, 6. A, 7. A, 8. B, 9. B, 10. C, 11. D, 12. D, 13. B, 14. A, 15. D, 16. D, 17. A AP CHEMISTRY UNIT 1 PART 2 REVIEW (Chapter 3) 1. Balance the following equations: a. CO(g) + O2(g) à CO2(g) b. N2O5(g) + H2O(l) à HNO3(aq) c. C5H10O2(l) + O2(g) à CO2(g) + H2O(g) d. Mg3N2(s) + H2SO4(aq) à MgSO4(aq) + (NH4)2SO4(aq) e. aluminum metal undergoes a combustion reaction with oxygen. f. copper (II) hydroxide decomposes into copper (II) oxide and water when heated. 2. Calculate the percentage by mass of oxygen in codeine, C18H21NO3. 3. Calculate the following quantities: a. mass, in grams, of 0.105 moles sucrose (C12H22O11) b. moles of zinc nitrate in 143.50 g of this substance c. number of molecules in 1.0 x 10-­‐6 mol CH3CH2OH. d. number of N atoms in 0.410 mol NH3. 4. The molecular formula of aspartame, the artificial sweetener marketed as NutraSweet® is C14H18N2O5. a. What is the molar mass of aspartame? b. How many moles of aspartame are present in 1.00 mg of aspartame? c. How many molecules are present in 1.00 mg of aspartame? d. How many hydrogen atoms are present in 1.00 mg of aspartame? AP Chem – Unit 1 Part 2 5. Determine the empirical and molecular formulas of ibuprofen, which contains 75.69% C, 8.80% H, and 15.51% O by mass. Ibuprofen has a molar mass of 206 g/mol. 6. Combustion analysis of toluene, a common organic solvent, gives 5.86 mg of CO2 and 1.37 mg of H2O. If the compound contains only carbon and hydrogen, what is its empirical formula? 7. When 5.061 g of Epsom salt (MgSO4·∙xH2O) is heated to 250°C, all the water of hydration is lost, leaving 2.472 g of MgSO4. What is the value of x? 8. Hydrofluoric acid cannot be stored in glass bottles because compounds called silicates in the glass are attacked by the HF(aq). Sodium silicate, for example, reacts as follows: Na2SiO3(s) + 8 HF(aq) à H2SiF6(aq) + 2 NaF(aq) + 3 H2O(l) How many grams of Na2SiO3 can react with 0.800 g of HF? 9. Solutions of sodium carbonate and silver nitrate react to form solid silver carbonate and a solution of sodium nitrate. A solution containing 3.50 g of sodium carbonate is mixed with one containing 5.00 g of silver nitrate. How many grams of sodium carbonate, silver nitrate, silver carbonate, and sodium nitrate are present after the reaction is complete? 10. When benzene reacts with bromine, bromobenzene is obtained: C6H6 + Br2 à C6H5Br + HBr a. What is the theoretical yield of bromobenzene in this reaction when 30.0 g of benzene reacts with 65.0 g of bromine? b. If the actual yield of bromobenzene was 42.3 g, what was the percentage yield? Marathon Problem: From the information below, determine the mass of substance C that will be formed if 45.0 grams of substance A reacts with 23.0 grams of substance B. (Assume that the reaction between A and B goes to completion.) a. Substance A is a gray solid that consists of an alkaline earth metal and carbon (37.5% by mass). It reacts with substance B to produce substances C and D. Forty million trillion formula units of A have a mass of 4.26 milligrams. b. 47.9 grams of substance B contains 5.36 grams of hydrogen and 42.5 grams of oxygen. c. When 10.0 grams of C is burned in excess oxygen, 33.8 grams of carbon dioxide and 6.92 grams of water and produced. A mass spectrum of substance C shows a parent molecular ion with a mass-­‐to-­‐charge ratio of 26. d. Substance D is the hydroxide of the metal in substance A. Answers: 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. a. 2 CO(g) + O2(g) à 2 CO2(g) b. N2O5(g) + H2O(l) à 2 HNO3(aq) c. 2 C5H10O2(l) + 13 O2(g) à 10 CO2(g) + 10 H2O(g) d. Mg3N2(s) + 4 H2SO4(aq) à 3 MgSO4(aq) + (NH4)2SO4(aq) e. 4 Al(s) + 3 O2(g) à 2 Al2O3(s) f. Cu(OH)2(s) à CuO(s) + H2O(g) 16.1% 17
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a. 35.9 g b. 0.7576 mol c. 6.0 x 10 molecules d. 2.47 x 10 N atoms -­‐6
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a. 294.30 g/mol b. 3.40 x 10 mol c. 2.05 x 10 d. 3.68 x 10 H atoms empirical and molecular formulas are both C13H18O2. C7H8 MgSO4·∙7H2O 0.610 g 1.94 g Na2CO3; 0 g AgNO3; 4.06 g Ag2CO3; 2.50 g NaNO3 a. 60.3 g b. 70.10% AP Chem – Unit 1 Part 2 AP Exam Questions: 1. Water is added to 4.267 grams of UF6. The only products are 3.730 grams of a solid containing only uranium, oxygen and fluorine and 0.970 gram of a gas. The gas is 95.0% fluorine, and the remainder is hydrogen. (a) From these data, determine the empirical formula of the gas. (b) What fraction of the fluorine of the original compound is in the solid and what fraction in the gas after the reaction? (c) What is the formula of the solid product? (d) Write a balanced equation for the reaction between UF6 and H2O. Assume that the empirical formula of the gas is the true formula. 2. The molecular formula of a hydrocarbon is to be determined by analyzing its combustion products and investigating its colligative properties. (a) The hydrocarbon burns completely, producing 7.2 grams of water and 7.2 liters of CO2 at standard conditions. What is the empirical formula of the hydrocarbon? (b) Calculate the mass in grams of O2 required for the complete combustion of the sample of the hydrocarbon described in (a). (c) The hydrocarbon is found to have a molecular weight of 56.2 g/mol. What is the molecular formula of the hydrocarbon? AP Chem – Unit 1 Part 2 3. A 0.150 g sample of solid lead(II) nitrate is added to 125 mL of 0.100 M sodium iodide solution. Assume no change in volume of the solution. The chemical reaction that takes place is represented by the following equation. Pb(NO3)2(s) + 2 NaI(aq) → PbI2(s) + 2 NaNO3(aq) (a) List an appropriate observation that provides evidence of a chemical reaction between the two compounds. (b) Calculate the number of moles of each reactant. (c) Identify the limiting reactant. Show calculations to support your identification. (d) Calculate the molar concentration of NO3–(aq) in the mixture after the reaction is complete. (e) Circle the diagram below that best represents the results after the mixture reacts as completely as possible. Explain the reasoning used in making your choice. AP Chem – Unit 1 Part 2 UNIT 2 HOME LEARNING PROBLEMS 1. Under appropriate experimental conditions, H2 and CO undergo a combination reaction to form CH3OH. The drawing below represents a sample of H2. Make a corresponding drawing of the CO needed to react completely with the H2. How did you arrive at the number of CO molecules in your drawing? 2. The following diagram represents the collection of elements formed by a decomposition reaction. (a) If the blue spheres represent N atoms and the red ones represent O atoms, what was the empirical formula of the original compound? (b) Could you draw a diagram representing the molecules of the compound that had been decomposed? Why or why not? 3. The following diagram represents the collection of CO2 and H2O molecules formed by complete combustion of a hydrocarbon. What is the empirical formula of the hydrocarbon? 4. Glycine, an amino acid used by organisms to make proteins, is represented by the molecular model below. AP Chem – Unit 1 Part 2 a. Write its molecular formula. b. Determine its molecular mass. c. Calculate the mass of 3 moles of glycine. d. Calculate the percent nitrogen by mass in glycine. 5. Nitrogen (N2) and hydrogen (H2) react to form ammonia (NH3). Consider the mixture of N2 and H2 shown in the accompanying diagram. The blue spheres represent N, and the white ones represent H. Draw a representation of the product mixture, assuming that the reaction goes to completion. How did you arrive at your representation? What is the limiting reactant in this case? 6. Balance the following equations: a. CO(g) + O2(g) à CO2(g) b. N2O5(g) + H2O(l) à HNO3(aq) c. CH4(g) + Cl2(g) à CCl4(l) + HCl(g) d. Al4C3(s) + H2O(l) à Al(OH)3(s) + CH4(g) AP Chem – Unit 1 Part 2 e. C5H10O2(l) + O2(g) à CO2(g) + H2O(g) f. Fe(OH)3(s) + H2SO4(aq) à Fe2(SO4)3(aq) + H2O(l) g. Mg3N2(s) + H2SO4(aq) à MgSO4(aq) + (NH4)2SO4(aq) h. Ca(OH)2(aq) + H3PO4(aq) à Ca3(PO4)2(s) + H2O(l) i. AgNO3(aq) + Na2SO4(aq) à Ag2SO4(s) + NaNO3(aq) j. CH3NH2(g) + O2(g) à CO2(g) + H2O(g) + N2(g) 7. Write balanced chemical equations to correspond to each of the following descriptions: a. When sulfur trioxide gas reacts with water, a solution of sulfuric acid forms. b. Boron sulfide, B2S3(s), reacts violently with water to form dissolved boric acid, H3BO3 and hydrogen sulfide gas. c. When an aqueous solution of lead (II) nitrate is mixed with an aqueous solution of sodium iodide, an aqueous solution of sodium nitrate and a yellow solid, lead iodide, are formed. d. When solid mercury (II) nitrate is heated, it decomposed to form solid mercury (II) oxide, gaseous nitrogen dioxide, and oxygen. e. Copper metal reacts with hot concentrated sulfuric acid solution to form aqueous copper (II) sulfate, sulfur dioxide gas, and water. f. Solid zinc metal reacts with sulfuric acid to form hydrogen gas and an aqueous solution of zinc sulfate. g. When liquid phosphorus trichloride is added to water, it reacts to form aqueous phosphorous acid, H3PO3(aq), and aqueous hydrochloric acid. h. When hydrogen sulfide gas is passed over solid hot iron (III) hydroxide, the resultant reaction produces solid iron (III) sulfide and gaseous water. AP Chem – Unit 1 Part 2 8. Balance the following equations, and indicate whether they are combination, decomposition, or combustion reactions: a. Al(s) + Cl2(g) à AlCl3(s) b. C2H4(g) + O2(g) à CO2(g) + H2O(g) c. Li(s) + N2(g) à Li3N(s) d. NH4NO3(s) à N2O(g) + H2O(g) e. K2O(s) + H2O(l) à KOH(aq) 9. Determine the formula weights of each of the following compounds: a. Nitric acid, HNO3 b. KMNO4 c. Ca3(PO4)2 d. Quartz, SiO2 e. Chromium (III) sulfate f. Benzoic acid, HC7H5O2, a substance used as a food preservative g. Urea, (NH2)2CO, a compound used as a nitrogen fertilizer h. Isopentyl acetate, CH3CO2C5H11, responsible for the odor of bananas 10. Calculate the percentage by mass of oxygen in the following compounds: a. Morphine, C17H19NO3 b. Codeine, C18H21NO3 c. Vancomycin, C66H75Cl2N9O24 AP Chem – Unit 1 Part 2 11. Calculate the percentage by mass of the indicated element in the following compounds: a. Carbon in acetylene, C2H2, a gas used in welding b. Hydrogen in ascorbic acid, HC6H7O6, also known as vitamin C c. Platinum in PtCl2(NH3)2, a chemotherapy agent called cisplatin d. Carbon in capsaicin, C18H27NO3, the compound that gives the hot taste to chili peppers 12. Calculate the following quantities: a. Mass, in grams, of 0.105 moles sucrose (C12H22O11) b. Moles of Zn(NO3)2 in 143.50 g of this substance c. Number of molecules in 1.305x10-­‐2 mol C6H6 d. Number of O atoms in 4.88x10-­‐3 mol Al(NO3)3 13. What is the mass, in grams, 2.50x10-­‐3 mole of ammonium phosphate? AP Chem – Unit 1 Part 2 14. How man moles of chloride ions are in 0.2550 g of aluminum chloride? 15. What is the mass, in grams, of 7.70x1020 molecules of caffeine, C8H10N4O2? 16. What is the molar mass of cholesterol if 0.00105 mol weighs 0.406 g? 17. What is the mass, in grams, of 0.0714 mol of iron (III) sulfate? 18. How many moles of ammonium ions are in 8.776 g of ammonium carbonate? 19. What is the molar mass of diazepam (Valium) if 0.05570 mol weighs 15.86 g? AP Chem – Unit 1 Part 2 20. The molecular formula of allicin, the compound responsible for the characteristic smell of garlic, is C6H10OS2. a. What is the molar mass of allicin? b. How many moles of allicin are present in 5.00 mg of this substance? c. How many molecules of allicin are in 5.00 mg of this substance? d. How many S atoms are present in 5.00 mg of allicin? 21. At least 25 µg of tetrahydrocannabinol (THC), the active ingredient in marijuana, is required to produce intoxication. The molecular formula for THC is C21H30O2. How many moles of THC does this 25 µg represent? How many molecules? 22. Give the empirical formula of each of the following compounds in a sample contains: a. 0.0130 mol C, 0.0390 mol H, and 0.0065 mol O b. 11.66 g iron and 5.01 g oxygen c. 40.0% C, 6.7% H, and 53.3% O by mass 23. Determine the empirical formulas of the compounds with the following compositions by mass: a. 10.4% C, 27.8% S, and 61.7% Cl b. 21.7% C, 9.6% O, and 68.7% F c. 32.79% Na, 13.02% Al, and 54.19% F AP Chem – Unit 1 Part 2 24. What is the molecular formula for the compound with an empirical formula NH2Cl, and molar mass equal to 51.5 g/mol. 25. Determine the empirical and molecular formulas of each of the following substances: a. Styrene, a compound substance used to make Styrofoam cups and insulation, contains 92.3% C and 7.7% H by mass and has a molar mass of 104 g/mol. b. Ibuprofen, a headache remedy, contains 75.69% C, 8.80% H, and 15.51% O by mass, and has a molar mass of 206 g/mol. 26. The characteristic odor of pineapple is due to ethyl butyrate, a compound containing carbon, hydrogen, and oxygen. Combustion of 2.78 mg of ethyl butyrate produces 6.32 mg of CO2 and 2.58 mg of H2O. What is the empirical formula of the compound? 27. Menthol, the substance we can smell in mentholated cough drops, is composed of C, H, and O. A 0.1005-­‐g sample of menthol is combusted, producing 0.2829 g of CO2 and 0.119 g of H2O. What is the empirical formula for menthol? If menthol has a molar mass of 156 g/mol, what is its molecular formula? AP Chem – Unit 1 Part 2 28. Epsom salts, a strong laxative used in veterinary medicine, is a hydrate, which means that a certain number of water molecules are included in the solid structure. The formula for Epsom salts can be written as MgSO4·∙xH2O, where x indicates the number of moles of H2O per mole of MgSO4. When 5.061 g of this hydrate is heated to 250 ⁰C, all the water of hydration is lost, leaving 2.472 g of MgSO4. What is the value of x? 29. Hydrofluoric acid, HF(aq), cannot be stored in glass bottles because compounds called silicates in the glass are attacked by the HF(aq). Sodium silicate (Na2SiO3), for example, reacts as follows: Na2SiO3 (s) + 8 HF (aq) à H2SiF6 (aq) + 2 NaF (aq) + 3 H2O (l) a. How many moles of HF are needed to react with 0.300 mol of Na2SiO3? b. How many grams of NaF form when 0.500 mol of HF reacts with excess Na2SiO3? c. How many grams of Na2SiO3 can react with 0.800 g of HF? 30. Several brands of antacids use Al(OH)3 to react with stomach acid, which contains primarily HCl: Al(OH)3 (s) + HCl (aq) à AlCl3 (aq) + H2O (l) a. Balance this equation. b. Calculate the number of grams of HCl that can react with 0.500 g of Al(OH)3. AP Chem – Unit 1 Part 2 c. Calculate the number of grams of AlCl3 and the number of grams of H2O formed when 0.500 g of Al(OH)3 reacts. d. Show that your calculation sin parts (b) and (c) are consistent with the law of conservation of mass. 31. Aluminum sulfide reacts with water to form aluminum hydroxide and hydrogen sulfide. a. Write the balanced chemical equation for this reaction. b. How many grams of aluminum hydroxide are obtained from 14.2 g of aluminum sulfide? 32. Calcium hydride reacts with water to form calcium hydroxide and hydrogen gas. a. Write a balanced chemical equation for the reaction. b. How many grams of calcium hydride are needed to form 8.500 g of hydrogen? 33. Sodium hydroxide reacts with carbon dioxide as follows: 2 NaOH (s) + CO2 (g) à Na2CO3 (s) + H2O (l) Which reagent is the limiting reactant when 1.85 mol NaOH and 1.00 mol CO2 are allowed to react? How many moles of Na2CO3 can be produced? How many moles of the excess reactant remain after the completion of the reaction? AP Chem – Unit 1 Part 2 34. The fizz produced when an Alka-­‐Seltzer tablet is dissolved in water is due to the reaction between sodium bicarbonate (NaHCO3) and citric acid (H3C6H5O7): 3 NaHCO3 (aq) + H3C6H5O7 (aq) à 3 CO2 (g) + 3 H2O (l) + Na3C6H5O7 (aq) In a certain experiment 1.00 g of sodium bicarbonate and 1.00 g of citric acid are allowed to react. a. Which is the limiting reactant? b. How many grams of carbon dioxide form? c. How many grams of the excess reactant remain after the limiting reactant is completely consumed? 35. Solutions of sodium carbonate and silver nitrate react to form solid silver carbonate and a solution of sodium nitrate. A solution containing 3.50 g of sodium carbonate is mixed with one containing 5.00 g of silver nitrate. How many grams of sodium carbonate, silver nitrate, silver carbonate, and sodium nitrate are present after the reaction is complete? AP Chem – Unit 1 Part 2 36. When benzene (C6H6) reacts with bromine (Br2), bromobenzene (C6H5Br) is obtained: C6H6 + Br2 à C6H5Br + HBr a. What is the theoretical yield of bromobenzene in this reaction when 30.0 g of benzene reacts with 65.0 g of bromine? b. If the actual yield of bromobenzene was 42.3 g, what was the percentage yield? 37. When hydrogen sulfide gas is bubbled into a solution of sodium hydroxide, the reaction forms sodium sulfide and water. How many grams of sodium sulfide are formed if 1.50 g of hydrogen sulfide is bubbled into a solution containing 2.00 g of sodium hydroxide, assuming that the sodium sulfide is made in 92.0% yield? 38. Consider a sample of calcium carbonate in the form of a cube measuring 2.005 in. on each edge. If the sample has a density of 2.71 g/cm3, how many oxygen atoms does it contain? 39. If an automobile travels 225 miles with a gas mileage of 20.5 mi/gal, how many kilograms of CO2 are produced? Assume that the gasoline is composed of octane, C8H18 (l), whose density is 0.69 g/mL, and that a combustion reaction has taken place. Repeat the calculation for a truck that has a gas mileage of 5 mi/gal.