Due: Asst. #19 Ch. 3 Problems: C2c, C6, D4, D5, D2ab, D6. In class: Notes for Asst. #20

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1 Chemistry Assignment Sheet Ch. 3 Stoichiometry In class: Notes for Asst. #18 Due: Asst. #18 Ch. 3 Problems: C2ab, C4, C5, D1. In class: Notes for Asst. #19 Due: Asst. #19 Ch. 3 Problems: C2c, C6, D4, D5, D2ab, D6. In class: Notes for Asst. #20 Due: Asst. #20 Ch. 3 Problems: D7, D9, H2abc. In class: Notes for Asst. #21 Due: Asst. #21 Ch. 3 Problems: H2d, {Balance only: E2, E3a, E4ac, E5c}. In class: Notes for Asst. #22 Due: Asst. #22 Ch. 3 Problems: E3bc, E4bde, E5abd, E6. In class: Notes for Asst. #23 Due: Asst. #23 Ch. 3 Problems: E7, E8, F1ab, F2ab. In class: Notes for Asst. #24 Due: Asst. #24 Ch. 3 Problems: G1a, G4a, G2b, G6. In class: discuss Hydrate lab In class: Hydrate Lab Due: Hydrate Lab Report & Review Asst. #25 Ch. 3 Problems: C3, D2cd, D8, E1, E5abd, E6, G5, H2a. In class: Sample Problems for Test Due: Review Asst. #26 Ch. 3 Problems: C2a, D3, E2bc, E3ab, E4cd, E5c, G1a. In class: Sample Problems for Test Due: Study Sheet (or Flash Cards) & 10 or more Practice Problems In class: Test Chapter 3 **Standards are due the day after the test!

2 Chemistry Ch. 3 Stoichiometry A. Atomic Masses and the Mass Spectrometer A1) Assume that element Uus is synthesized and that it has the following stable isotopes: 284 Uus (283.4 amu) 34.60% 285 Uus (284.7 amu) 21.20% 288 Uus (287.8 amu) 44.20% What is the value of the average atomic mass for Uus that would be listed on the periodic table? A2) An element is a mixture of two isotopes. One isotope of the element has an atomic mass of amu and has a relative abundance of 75.53%. The other isotope has an atomic mass of amu. Calculate the average atomic mass and identify the element. A3) An element consists of 1.40% of an isotope with mass amu, 24.10% of an isotope with mass amu, 22.10% of an isotope with mass amu, and 52.40% of an isotope with mass amu. Calculate the average atomic mass and identify the element. A4) The element europium exists in nature in two isotopes. 151 Eu has a mass of amu and 153 Eu has a mass of amu. The average atomic mass of europium is amu. Calculate the relative abundance of the two europium isotopes. A5) The element rhenium (Re) has two naturally occurring isotopes, 185 Re and 187 Re, with an average atomic mass of amu. Rhenium is 62.60% 187 Re and the atomic mass of 187 Re is amu. Calculate the mass of 185 Re. B. Moles and Molar Masses B1) How many Fe atoms and how many moles of Fe atoms are in 500. g of iron? B2) Diamond is a natural form of pure carbon. How many atoms of carbon are in a 1.00 carat diamond (1.00 carat = g)? B3) Calculate the molar mass of the following substances. a) NH 3 b) N 2 H 4 c) (NH 4 ) 2 Cr 2 O 7 B4) Calculate the molar mass of the following substances. a) P 4 O 6 b) Ca 3 (PO 4 ) 2 c) Na 2 HPO 4 B5) How many moles are present in 1.00 g of each of the compounds in Question B3? B6) How many grams are present in 5.00 mol of each compound in Question B3? B7) How many molecules are present in 1.00 g of each compound in Question B3? B8) Ascorbic acid, or vitamin C (C 6 H 8 O 6 ), is an essential vitamin, that cannot be stored by the body and must be present in the diet. A typical tablet contains 500. mg of vitamin C. How many moles and molecules of vitamin C does this 500. mg tablet contain? B9) Aspirin (acetylsalicylic acid, C 9 H 8 O 4 ) is one of the most commonly used pain relievers. A typical tablet contains 500. mg of aspirin. How many moles and molecules are in a 500. mg tablet of aspirin? B10) How many moles are represented by each of the following? a) 100. molecules of H 2 O b) g H 2 O c) 150 molecules (exactly) of O 2 B11) Determine the mass in grams of the following: a) 3.00 X10 20 molecules of N 2 b) 3.00 X10-3 mol N 2 B12) Aspartame, C 14 H 18 N 2 O 5, is an artificial sweetener that is 160 times sweeter than sucrose (table sugar) when dissolved in water. a) Calculate the molar mass of aspartame. b) How many moles are present in 10.0 g of c) How many grams are in 1.56 mol of d) How many molecules are in 5.0 mg e) How many atoms of nitrogen are in 1.2 g f) How many grams are in 1.0 X10 9 molecules of g) How many grams are in 1.00 molecule of

3 Chemistry Ch. 3 Stoichiometry B13) Humulone, C 21 H 30 O 5, is one of the flavor components that gives the hops in beer a bitter taste. a) What is the molar mass of humulone? b) How many molecules are in 275 mg of humulone? c) What is the mass of mols of humulone? d) How many atoms of hydrogen are in 1.00 pg of humulone? e) What is the mass of 1.00 X10 9 molecules of humulone? f) What is the mass of 1.0 molecule of humulone? C. Percent Composition C1) Photocells use a semiconducting material that produces an electric current or a change in resistance on exposure to light. Cd compounds are commonly used in photocells. Calculate the mass percent of Cd in CdS, CdSe and CdTe. C2) Calculate the percent composition by mass in the following starting materials for synthetic polymers (plastics). a) C 3 H 4 O 2 (acrylic acid, from which acrylic plastics are made) b) C 4 H 6 O 2 (methyl acrylate, from which Plexiglas is made) c) C 3 H 3 N (acrylonitrile, from which Orlon is made) C3) In 1987 the first substance to act as a superconductor above 77 K (the temperature of liquid nitrogen) was discovered. Calculate the percent composition of this superconductor, YBa 2 Cu 3 O 7. C4) Calculate the mass percent of carbon for each of the following substances and then arrange the substances in order of increasing mass percent of carbon. Caffeine, C 8 H 10 N 4 O 2 Sucrose, C 12 H 22 O 11 Ethanol, C 2 H 5 OH C5) Vitamin B 12, cyanocobalamin, is essential for human nutrition. Since vitamin B 12 is in animal tissue, but not in higher plants, vegetarians may become deficient in vitamin B 12. Cyanocobalamin contains 4.34% cobalt by mass. Calculate the molar mass of cyanocobalamin, if there is one cobalt atom in each molecule of cyanocobalamin. C6) Fungal laccase, a blue protein found in wood-rotting fungi is 0.390% Cu by mass. If a fungal laccase molecule contains 4 copper atom, what is the molar mass of fungal laccase? D. Empirical and Molecular Formulas D1) Give the empirical formula for each of the following compounds. a) vitamin C, C 6 H 8 O 6 b) benzene, C 6 H 6 c) acetylene, C 2 H 2 d) phosphorus pentoxide, P 4 O 10 e) glucose, C 6 H 12 O 6 f) acetic acid, HC 2 H 3 O 2 D2) Determine the molecular formulas to which the following empirical formulas and molar masses pertain. a) SNH ( g/mol) b) NPCl 2 ( g/mol) c) CoC 4 O 4 ( g/mol) d) SN ( g/mol) D3) One of the most commonly used white pigments in paint is a compound of titanium and oxygen that contains 59.9% Ti by mass. Determine the empirical formula of this compound. D4) The compound adrenalin contains 56.79% C, 6.56% H, 28.37% O and 8.28% N by mass. What is the empirical formula for adrenaline? D5) A sample of urea contains g N, g H, g C and g O. What is the empirical formula of urea? D6) A compound that contains only nitrogen and oxygen is 30.4% N by mass. The molar mass of the compound is 92 g/mol. What is the empirical formula of the compound? What is the molecular formula of the compound? D7) A compound containing only sulfur and nitrogen is 69.6% S by mass. The molar mass is 184 g/mol. What are the empirical and molecular formulas of the compound?

4 Chemistry Ch. 3 Stoichiometry D8) Benzene contains only carbon and hydrogen and is 7.74% H by mass. The molar mass is 78.1 g/mol. Determine the empirical and molecular formulas of benzene. D9) Adipic acid is an organic compound composed of 49.31% C, 43.79% O and the rest hydrogen. If the molar mass of adipic acid is g/mol, what are the empirical and molecular formulas for adipic acid? D10) Many homes in rural America are heated by propane gas, a compound that only contains carbon and hydrogen. Complete combustion of a sample of propane produced g of carbon dioxide and g of water as the only products. Find the empirical formula of propane. D11) A compound contains only C, H, and N. Combustion of 35.0 mg of the compound produces 33.5 mg CO 2 and 41.1 mg H 2 O. What is the empirical formula of the compound? D12) Cumene is a compound containing only carbon and hydrogen that is used in the production of acetone and phenol in the chemical industry. Combustion of 47.6 mg cumene produces some CO 2 and 43.8 mg water. The molar mass of cumene is between 115 and 125 g/mol. Determine the empirical and molecular formulas. D13) A compound contains only carbon, hydrogen, and oxygen. Combustion of mg of the compound yields mg CO 2 and 4.37 mg H 2 O. The molar mass of the compound is g/mol. What are the empirical and molecular formulas of the compound? E. Balancing Chemical Equations E1) Write the balanced chemical equation that describes each of the following: a) Iron metal reacts with oxygen to form rust, iron III oxide. (Remember: all gases are diatomic, X 2, except noble gases which are alone, X) b) Calcium metal reacts with water to produce aqueous calcium hydroxide and hydrogen gas. c) Aqueous barium hydroxide reacts with aqueous sulfuric acid to produce solid barium sulfate and water. E2) Balance the following equations and state a) Cu (s) + AgNO 3(aq) Ag (s) + Cu(NO 3 ) 2(aq) b) Zn (s) + HCl (aq) ZnCl 2(aq) + H 2(g) c) Au 2 S 3(s) + H 2(g) Au (s) + H 2 S (g) E3) Balance the following equations and state a) Ca(OH) 2(aq) + H 3 PO 4(aq) H 2 O (l) + Ca 3 (PO 4 ) 2(aq) b) Al(OH) 3(s) + HCl (aq) AlCl 3(aq) + H 2 O (l) c) AgNO 3(aq) + H 2 SO 4(aq) Ag 2 SO 4(s) + HNO 3(aq) E4) Balance the following equations and state a) C 12 H 22 O 11(s) + O 2(g) CO 2(g) + H 2 O (g) b) C 6 H 6(l) + O 2(g) CO 2(g) + H 2 O (g) c) Fe (s) + O 2(g) Fe 2 O 3(s) d) C 4 H 10(g) + O 2(g) CO 2(g) + H 2 O (l) e) FeO (s) + O 2(g) Fe 2 O 3(s) E5) Balance the following equations and state a) Cr (s) + S 8(s) Cr 2 S 3(s) b) heat + NaHCO 3(s) Na 2 CO 3(s) + CO 2(g) + (The heat can be ignored.) H 2 O (g) c) heat +KClO 3(s) KCl (s) + O 2(g) d) Eu (s) + HF (g) EuF 3(s) + H 2(g) E6) Silicon is produced for the chemical and electronics industry by the following reactions. Balance the following equations: a) SiO 2(s) + C (s) Si (s) + CO (g) b) SiCl 4(s) + Mg (s) Si (s) + MgCl 2(s) c) Na 2 SiF 6(s) + Na (s) Si (s) + NaF (s) E7) Lead hydrogen arsenate, an inorganic insecticide used against the potato beetle, is a product in the following reaction. Balance this equation. Pb(NO 3 ) 2(aq) + H 3 AsO 4(aq) PbHAsO 4(s) + HNO 3(aq) E8) The electrolysis of concentrated brine solutions (salt water) is an important source of NaOH, H 2, and Cl 2 for the chemical industry. Balance this equation. electricity + NaCl (aq) + H 2 O (l) Cl 2(g) + H 2(g) + (The electricity can be ignored.) NaOH (aq)

5 F. Reaction Stoichiometry F1) Over the years, the thermite reaction has been used for welding railroad rails, incendiary bombs, and to ignite solid fuel rockets. The reaction is Fe 2 O 3(s) + 2 Al (s) 2Fe (l) + Al 2 O 3(s) a) If 15.0 g iron is produced, what mass of iron III oxide must be used? b) If 15.0 g iron is produced, what mass of aluminum must be used? c) If 15.0 g iron is produced, what mass of aluminum oxide is produced? F2) The compound cisplatin, Pt(NH 3 ) 2 Cl 2, has been studied extensively as an antitumor agent. Cisplatin is synthesized as follows: K 2 PtCl 4(aq) + 2 NH 3(aq) Pt(NH 3 ) 2 Cl 2(s) + 2 KCl (aq) a) What mass of cisplatin, Pt(NH 3 ) 2 Cl 2, can be made from 100. g of K 2 PtCl 4? b) What mass of KCl can be made from 100. g of K 2 PtCl 4? G. Limiting Reagent and Percent Yield G1) When a mixture of silver metal and sulfur is heated, silver sulfide is formed: heat + 16 Ag (s) + S 8(s) 8 Ag 2 S (s) a) What mass of Ag 2 S is produced from a mixture of 2.0 g Ag and 2.0 g S 8? b) What mass of which reactant is left unreacted? G2) Mercury and bromine will react with each other to produce mercury II bromide: Hg (l) + Br 2(l) HgBr 2(s) a) What mass of HgBr 2 can be produced from the reaction of 10.0g Hg and 9.00 g Br 2? What mass of which reagent is left unreacted? b) What mass of HgBr 2 can be produced from the reaction of 5.00 ml Hg (density = 13.6 g/ml) and 5.00 ml Br 2 (density = 3.10 g/ml)? G3) Consider the following unbalanced equation: Ca 3 (PO 4 ) 2(s) + H 2 SO 4(aq) CaSO 4(s) + H 3 PO 4(aq) a) What mass of calcium sulfate can be produced from the reaction of 1.0 kg calcium phosphate with 1.0 kg concentrated sulfuric acid (98% H 2 SO 4 by mass)? b) In part a what mass of phosphoric acid would be produced? G4) Hydrogen cyanide is produced industrially from the reaction of gaseous ammonia, oxygen, and methane: 2 NH 3(g) + 3 O 2(g) + 2 CH 4(g) 2 HCN (g) + 6 H 2 O (g) a) If 5.00 X10 3 kg each of NH 3, O 2, and CH 4 are reacted, what mass of HCN will be produced, assuming 100% yield? b) In part a how much H 2 O will be produced, assuming 100% yield? G5) A student prepared aspirin in the laboratory experiment, reacting 1.50 g salicylic acid with 2.00g acetic anhydride. The experimental yield was 1.50 g aspirin. Calculate the theoretical yield of aspirin and the percent yield for this experiment. C 7 H 6 O 3 + C 4 H 6 O 3 C 9 H 8 O 4 + HC 2 H 3 O 2 salicylic acetic aspirin acetic acid anhydride acid G6) Aluminum burns in bromine, producing aluminum bromide: 2 Al (s) + 3 Br 2(l) 2 AlBr 3(s) In a certain experiment, 6.0 g Al was reacted with an excess of bromine to yield 50.3 g aluminum bromide (experimental yield). Calculate the theoretical and percent yields for this experiment. G7) Consider the following unbalanced reaction: P 4(s) + F 2(g) PF 3(g) How many grams of F 2 are needed to produce 120. g of PF 3, if the reaction has a 78.1% yield? H1) Terepthalic acid is an important chemical used in the manufacture of polyesters and plasticizers. It contains only C, H, and O. Combustion of mg terepthalic acid produces mg CO 2 and 6.45 mg H 2 O. The molar mass of terepthalic acid is 166 g/mol. Calculate the empirical and molecular formulas for terepthalic acid. H2) Find the formula of the following hydrates: a) g MgSO 3 and g H 2 O b) 95.3 g LiNO 3 and 74.7 g H 2 O c) 76.9 % CaSO 3 and 23.1 % H 2 O d) 89.2% BaBr 2 and 10.8% H 2 O

6 Hydrated Crystals (15pts) Some crystals form with water trapped in the crystal s structure. In other crystals, just sitting in air is enough for the water molecules to become incorporated into the crystal s structure. These crystals are hydrates. By heating a hydrate, the water held within the crystal can be forced out of the crystal and into the air. By calculations, it is possible to find out the formula of the hydrate. Materials: CuSO 4?H 2 O, Crucible, Desiccator, Clay triangle support Procedure: 1) Wipe out a crucible with tissue until clean of debris. Don t worry about any stains! Do not get the crucible wet! 2) Heat the crucible for about 20 sec to drive out any moisture. 3) When the crucible can be held in the hand without burning, measure the mass. (The balance will not weigh accurately, if the object being massed is hot!) 4) Add about 0.50 g of CuSO 4?H 2 O to the crucible and then measure the mass of the crucible containing the CuSO 4?H 2 O. 5) Heat the crucible until the CuSO 4?H 2 O has all changed to a lighter color. The color of the CuSO 4?H 2 O should turn to a light blue. It will lighten first from the edges, then going in to the center. If the crucible is too hot, it may turn green or brownish in color. If the bottom of the crucible is glowing red, it is too hot. If it is getting too hot, turn down the fire. ** Do not breathe the fumes. The CuSO 4?H 2 O is toxic.** 6) When all of the CuSO 4?H 2 O is lighter in color (around 5 minutes But you have to watch it!), turn off the fire. Move the crucible to the desiccator with the crucible tongs. Have a lab partner open the lid for you. The desiccator provides a water free environment for the crucible to cool off in. Drierite is in the bottom of the desiccator to absorb water. (The Drierite is CaSO 4 plus an indicator, which changes color from blue to pink as it absorbs water.) 7) Keep it in the desiccator for about 10 minutes or until the crucible can be held in the hand without burning. Then measure the mass of the crucible containing the CuSO 4 without water. 8) Dump the CuSO 4 into the waste container and wipe out the crucible with a tissue. Put back the clay triangle support. Prelab Calculations: 1) Find the mass of the water that evaporated upon heating. Mass of crucible is g Mass of crucible and CuSO 4?H 2 O is g Mass of crucible and CuSO 4 after heating is g 2) Find the mass of the CuSO 4 (without water). 3) Find the mols of water evaporated. 4) Find the mols of CuSO 4. 5) Find the ratio of mols water to mols CuSO 4. 6) Write the formula for the hydrate CuSO 4?H 2 O. (Round off to a whole number.) Calculations: 1) Calculate the formula for CuSO 4?H 2 O. Use the same steps as the prelab. (5pts) 2) What will happen to the color of the light blue CuSO 4, if it sits out? Why did you let it cool down in the desiccator? (2pts) Conclusion: State the hydrate formula. Discuss errors and what was learned. (3pts)