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# Problems For Stoichiometry

## by Ariane Rosos, Educator at Philippine Science High School - Main Campus on Aug 27, 2009

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## Problems For StoichiometryDocument Transcript

• NAME_________________________________________SECTION:adelfa,champa,dahlia,jasmin,sampa Calculate the molar mass of the following compounds a. ZnCl2 b. Ca(CN)2 c. Cu(OH)2 d. Ba(NO3)2 e. K3PO4 f. Hg2S g. (NH4)2SO4 h. FeF3 i. Na2CrO4 j. Cr2(CO3)3 k. Al2O3 l. Cu(ClO4)2 m. NiCO3 n. SnBr2 o. Fe(OH)2 PART 1 - Stoichiometry I – Mole Calculations – Lecture Notes 1. How many moles are 2.80 x 1024 atoms of silicon? 2. How many atoms are 0.360 mol Ag? 3. How many molecules are 4.00 mol glucose, C6H12O6? 4. How many iron atoms are present in a sample of iron metal with 2.35 mol Fe? 5. How many atoms of gold are present in 5.07 x 10-3 mol Au? 6. How many moles of sulfur are present in a sample containing 7.65 x 1022 S atoms? What is the mass of this sample? 7. What is the mass of 2.35 x 1024 atoms Cu? 8. How many atoms are present n a 22.6 g sample of He gas? 9. Calculate the quantities indicated. a. the number of moles represented by 2.18 x 1026 Fe atoms b. the mass, in grams, of 7.71 mol Kr c. the mass, in mg, of a sample containing 6.15 x 1019 Au atoms 1
• d. the number of atoms in 112 cm3 of Fe (d= 7.86 g/cm3) 10. How many a) grams of H2S b)moles of H c) moles of S d) grams of H e) grams of S f) molecules of H2S d) atoms of H e) atoms of S are contained in 0.400 mol H2S? 11. How many grams of each constituent element are contained in one mole of a. CH4 b. Fe2O3 c. Ca3P2 12. Calcium dihydrogen phosphate, Ca(H2PO4)2 is an ingredient in baking powder. It is an ionic compound consisting of Ca2+ and H2PO4 ions a. How many of each ion is present in 1 mole of the compound? b. What is the mass of one mole of compound? 13. How many atoms of hydrogen are there in 6.08 g of ammonium sulfate (NH4)2SO4? 14. How many moles of Ba and of Cl are contained in 107.0 g of Ba(ClO3)2•H2O? How many molecules of water of hydration are in this same amount? 15. How many moles of Fe and S are contained in a. 1 mol of FeS2(pyrite) b. 1 kg of FeS2 16. The amino acid methionine is essential in human diets. It has the molecular formula C5H11NO2S. Determine a. it molecular mass 2
• b. the number of moles of H atom per mole methionine c. the number of grams of C per mole of methionine d. the number of C atoms in 9.07 mole methionine 17. Determine the mass, in grams, of a quantity of the amino acid lysine, C6H14N2O2, containing 1.15 mol N atoms. 18. The hemoglobin content of blood is about 15.5 g/100 mL blood. The molar mass of hemoglobin is about 64,500 g/mol, and there are four Fe atoms in a hemoglobin molecule. Approximately how many Fe atoms are present in the 6L of blood in a typical adult? 19. How many moles of F are in a 75.0 mL sample of halothane (C2HBrClF3) (d = 1.871 g/ml) PERCENT COMPOSITION 1. What is the mass percent composition of halothane, C2HBrClF3? ( molar mass = 197.38 g/mol) 2. Adenosine triphosphate (ATP) is the main energy storage molecule in cells. Its chemical formula is C10H11N5P3O13. What is its mass percent composition? 3. Caffeine is a bitter tasting compound that is present in coffee and tea and added to cola soft drinks. Its chemical formula is C8H10N4O2. What is the percent composition of the elements in caffeine? Empirical Formula and Molecular Formula 1. An unknown sample was analyzed and found to contain 3.60 g carbon, 0.61 g hydrogen and 38.07 g iodine. What is the empirical formula of the compound? If its molecular mass is 281.86 amu, what is the molecular formula of the compound? 3
• 2. A compound was found to have the following percentage composition: Pb = 70.19%, Carbon = 8.14%, and Oxygen = 21.67 %. What is the empirical formula of the compound? 3. A white crystalline compound obtained from tonka bean was observed to have the odor of vanilla and has the following compositions: C = 73.97 % , H = 4.14%, O = 21.89%. What is the empirical formula of the compound? PART 2 - Stoichiometry I – Mole Calculations 1. What is the mass in grams of 1.00 mole of each of the following elements? a. Magnesium b. Fluorine c. Iron d. Cadmium 2. Given 100.00 g of each of the following elements find the number of moles. a. Calcium b. Potassium b. Nickel d. Tin d. Lead 3. Calculate the number of atoms in each of the above elements in 100.00 g of the element? 4. Find the formula mass of the following substances. a)KF b) MgCl2 c)CuSO4 4
• d) ZnCO3 e)(NH4)3PO4 e) C10H19PS2O6 (malathion) f) KAl(SO4)2 • 12 H2O (Alum) 5. Calculate the number of moles present in 100.00 grams of the compound given above. 6. What is the mass in grams of 3.61 x 1022 atoms of a) Xe b) N c)Au d)Sc e)K 7. Find the mass of 0.25 mole of the following substances. a) K2CrO4 b) CH4 c) SiH4 d) AlPO4 e) Ba(OH)2 8. How many moles are in 250 grams of a) PbSO4 b) Fe2O3 c) CH3CHO d) CH3CH2OH 5
• 9. Calculate the mass in grams of one molecule of a) Bromine, Br2 b)Hydrazine, N2H4 10. The gem emerald is a pure crystal of the mineral beryl, Be3Al2(SiO3)6. How many atoms of beryllium would be in 134.35 grams beryl? 11. Which among the following amounts contains the most number of atoms? a) 2.0 grams of potassium metal. b) 0.3 moles of hydrogen atoms c) 1.204 x 1021 atoms of sulfur d) 1.27 g of iodine 12. What is the mass of oxygen combined with 15.76 g of gold in a sample of gold oxide, Au2O? 13. The most important solid fertilizer used around the world is ammonium sulfate, (NH4)2SO4. In 20.0 grams of (NH4)2SO4, calculate the following: a. moles of (NH4)2SO4 b. moles of nitrogen atoms c. moles of sulfur atoms 6
• d. atoms of hydrogen atoms e. atoms of oxygen 14. Calculate the mass of oxygen combined with 2.874 grams of titanium in a sample of the mineral, rutile, TiO2. 15. Calculate the mass in grams of oxygen required to react with 5.00 x 10 20 molecules of P4 to produce phosphorus pentoxide, P4O10. 16. Calculate the percentage composition of each of the following: a. KCN b. CaF2 c. Ag3PO4 d. Na2HPO4 e. C6H2(CH3)(NO2)3 17. An unknown compound was found to have a mass ratio of 4.33 chromium to 2.0 oxygen. a. Determine the percentage composition of the compound. b. Calculate the mass in grams of oxygen that combines with 2.60 g of chromium to produce the compound. c. In 2.28 gram of the compound how many grams of chromium are there? How many grams of sulfur? d. Calculate the mass in grams of the compound produced when 15.0 grams chromium completely reacts with oxygen. 7
• 18. What is the empirical formula of the compound that contains 71.73% Sb and 28.27% O. 19. A 10.28 gram sample of an oxide of bismuth was found to contain 8.36 g of bismuth. What is the empirical formula of the compound? 20. Putrescine, the substance responsible for the odor of decaying fish, has the following percentage composition: Carbon = 54.50%, Hydrogen = 13.72% Nitrogen 31.78% It’s molecular mass is 88.15 amu. Determine it’s empirical and molecular formula. 21. A 0.0175 gram sample of the insecticide, DDT, was found to contain: 8.4 x 10 -4 g carbon, 4.53 x 10-4 g hydrogen and 8.88 x 10-3 g chlorine. a. What is the empirical formula of DDT? b. What is it’s molecular formula if it’s molar mass is 350? Stoichiometry II - Mole Calculations/ Limiting and Excess Reagent – Lecture Notes 1. Given the balanced equation N2(g) + 3H2(g) → 2NH3(g) How many moles of ammonia are produced when 0.60 mol of nitrogen reacts with hydrogen? 2. Given the equation: SiO2 + HF → SiF4 + H2O a. Calculate the number of moles HF that would completely react with 2.5 moles of SiO2. b. Calculate the number of moles SiF4 formed by completely reacting 2.5 moles SiO2 with HF. c. Calculate the mass of water formed by reacting 2.5 moles SiO2 with HF. 8
• d. Calculate the number of water molecules formed by reacting 2.5 moles SiO2 with HF. e. Calculate the mass of oxygen formed by reacting 2.5 moles SiO2 with HF. 3. Calculate the number of grams NH3 produced by the reaction of 5.40 grams of hydrogen with an excess nitrogen. 4. The overall reaction for the conversion of sugar(glucose) to acetic acid is: C6H12O6 + 2O2 → 2CH3COOH + 2CO2 + 2H2O A given volume of nipa sap contains 69.0 g of glucose. If all of this sugar is fermented , how many grams of acetic acid would be produced? 5. How many molecules of oxygen are produced when 29.2 g of water is decomposed forming hydrogen gas and oxygen gas? 6. 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) → H2SiF6(aq) + 2NaF(aq) + 3H2O(l) a. How many moles of HF are needed to react with 0.300 mol Na2SiO3? b. How many grams of NaF form when 0.500 mol of HF reacts with excess sodium silicate? c. How many grams sodium silicate can react with 0.800 g of HF? 7. Automotive air bags inflate when sodium azide, NaN3, rapidly decomposes to its component elements: 2 NaN3(s) → 2Na(s) + 3N2 (g) a. How many moles of N2 are produced by the decomposition of 2.50 mol NaN3? b. How many grams of NaN3 are required to form 6.00 g of nitrogen gas? 9
• 8. The complete combustion of octane, C8H18, a component of gasoline, proceeds as follows: 2C8H18(l) + 25 O2 (g) → 16 CO2(g) + 18 H2O(g) a. How many moles of O2 are needed to burn 0.750 mol of C8H18? b. How many grams of O2 are needed to burn 5.00 g of C8H18 ? 9. Detonation of nitroglycerin proceeds as follows: 4C3H5N3O9 (l) → 12 CO2(g) + 6N2(g) + O2(g) + 10H2O (g) a) If a sample containing 3.00 mL of nitroglycerin ( d = 1.592 g/ml) is detonated, how many total moles of gas are produced? b) How many grams of N2 are produced in the detonation? Limiting Reagents and Excess Reagents 1. Sodium chloride can be prepared by the reaction of sodium metal with chlorine gas. 2Na(s) + Cl2(g) → 2NaCl(s) a. If 6.70 mol Na reacts with 3.20 mol Cl2 what it the limiting reagent? b. How many moles of NaCl are produced? c. How much of the excess reagent remains unreacted? 2. Phosphorus trichloride, PCl3 is commercially important compound used in the manufacture of pesticides, gasolines, additives, and number of other products. It is made by the direct combination of phosphorus and chlorine. P4 + 6Cl2 → 4PCl3 What mass of PCl3 forms in the reaction of 125 g P4 with 323 g Cl2? 3. Sodium hydroxide reacts with carbon dioxide as follows; 2NaOH(s) + CO2 (g) → Na2CO3 (s) + H2O (l) a. Which reagent is a limiting reactant when 1.70 mol NaOH and 1.00 mol CO2 are allowed to react? b. How many moles of Na2CO3 can be produced? c. How many moles of the excess reactant remain after the completion of the reaction? 10
• 4. The fizz produced when Alka-Seltzer tablet is dissolved in water is due to the reaction between sodium bicarbonate (NaHCO3) and citric acid ( H3C6H5O7) : 3NaHCO3 (aq) + H3C6H5O7 (aq) → 3CO2(g) + 3H2O(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 excess reactant remained after the limiting reactant is completely consumed? 5. One of the steps in the commercial process for converting ammonia to nitric acid is conversion of NH3 to NO: 4NH3 (g) + 5O2 (g) → 4NO(g) + 6H2O(g) In a certain experiment, 2.25 g of NH3 reacts with 3.75 g of O2. a. Which is the limiting reactant b. How many grams of NO forms? c. How many grams of excess reactant remain after the limiting reactant is completely consumed? 6. Solutions of sodium carbonate and silver nitrate react to form solid silver carbonate and a solution of silver nitrate. A solution containing 6.50 g sodium carbonate is mixed with one containing 7.00 g silver nitrate. How many grams of sodium carbonate, silver nitrate, silver carbonate, and sodium nitrate are present after the reaction is complete 11
• 7. Solutions of sulfuric acid and lead(II) acetate react to form solid lead(II) sulfate and a solution of acetic acid. If 7.50 g of sulfuric acid and 7.50 g of lead(II) acetate are mixed, calculate the number of grams of sulfuric acid, lead(II) acetate, lead(II) sulfate, and acetic acid present in the mixture after the reaction is complete. 8. Turpentine, a hydrocarbon commonly used as paint thinner, burst into flame when warmed and place in contact with chlorine. C10H16 + Cl2 → HCl + 10C a) How many moles of HCl are formed from 0.025 mole C10H16? b) How many moles of Cl2 are required to react with 3.6 g C10H16? c) Calculate the mass of C produced when the amount of C10H16 given above in (b) reacts with Cl2? d) Calculate the number of C atoms produced in (b). 9. Copper is obtained from copper ores by roasting and smelting. The process may be represented by the overall equation: 2CuFeS2 + 5O2 → 2Cu + 2FeO +4SO2 a) What mass of copper may be obtained from 100 kg of CuFeSs? b) How many moles of O2 would be required for the reaction? c) Calculate the number of molecules of SO2 that would be produced? 10. The ozone hole in the Antartic is growing. Chlorofluorocarbons (CFC) produced by humans and used as coolants in air conditioners and refrigerators have been pointed at as the culprits. One such CFC compound is dichlorodifuoromethane or Freon-12. A reaction involved in the production of Freon-12 is as follows: CCl4 + SbF3 → CCl2F2 + SbCl2 F a) Determine the mass in grams of CCl4 required to completely react with 25.75 g of SbF3. b) Calculate the mass in grams and the number of molecules of Freon-12 (CCl2F2) that would be produced from the reaction. 12
• 11. Aspirin, C9H8O4 is prepared from the reaction of salicylic acid (C7H6O3) and acetic anhydride (C4H6O3). The reaction is C7H6O3 + C4H6O3 → C9H8O4 + C2H4O2 If 40 grams of salicylic acid and 150 grams of acetic anhydride were allowed to react, a) What mass of aspirin would be produced? b) Which is the limiting reactant? c) Which is the reactant present in excess? d) What mass of the reactant in excess remains unreacted? Theoretical Yield, Actual Yield, and Percentage Yield 1. Wine is produced by the fermentation of fruit sugars to alcohol. The chemical reaction is C6H12O6 → 2CH3CH2OH + 2CO2 Five kilograms of banana pulp containing 625 grams of fructose was used in preparation of banana wine. What is the percentage yield if, at the end of fermentation 218 g of ethanol was produced? 2. Tuba is an alcoholic drink produced by the spontaneous fermentation of sap collected from coconut inflorescence. Yeasts convert sucrose and other sugars to alcohol. The conversion of sucrose to ethanol may be represented by the chemical equation: C12H22O11 + H2O → 4 CH3CH2OH + 4 CO2 Coconut sap contains 16.5 grams/100 mL C12H22O11. What volume of sap must a tuba gatherer collect to produce tuba containing 598 g of alcohol, CH3CH2OH, if the efficiency of the fermentation process is 66.7 percent? 3. A 15.6 gram sample of C6H6 is mixed with excess HNO3. We isolate 18.0 grams of C6H5NO2. What is the percent yield of C6H5NO2? C6H6 + HNO3 → C6H5NO2 + H2O Determination of Molecular Formula Using Combustion Analysis 13
• 1. A 0.1014 gram sample of purified glucose was burned in a C-H combustion train to produce 0.1468 gram of CO2 and 0.0609 gram of H2O. An elemental analysis showed that glucose contains only carbon, hydrogen and oxygen. Determine the masses of C, H and O in the sample. Determine the EF and MF. 2. Complicated chemical reactions occur at hot springs on the ocean floor. One compound obtained from such hot spring consists of Mg, Si, H, and O. From a 0.334 gram sample, the Mg is recovered as 0.115 g of MgO; H is recovered as 25.7 mg of H2O; and Si is recovered as 0.172 g of SiO2. What is the simplest formula of this compound? Sequential Reactions 1. Consider the two step process for the formation of tellurous acid described by the following equations: TeO2 + 2OH- → TeO33- + H2O TeO32- + 2H+ → H2TeO3 What mass of H2TeO3 would be formed from 62.1 g of TeO2, assuming 100% yield? 2. Consider the formation of cyanogens, C2N2, and its subsequent decomposition in water given by the equations 2Cu2+ + 6CN- → 2[Cu(CN)2]- + C2N2 C2N2 + H2O → HCN + HOCN How much cyanic acid, HCN, can be produced from 10.00 g of KCN, assuming 100% yield? 3. What mass of potassium chlorate would be required to supply the proper amount of oxygen needed to burn 35.0 g of methane, CH4? 2 KClO4 → 2KCl + 3O2 CH4 + 2O2 → CO2 + 2H2O --- inihanda ni Sir Paz para sa mga mababait nyang estudyante sa Pisay… 14