9.) A chloride of rhenium contains 63.6% rhenium. What is the formula of this compound? (ReCl 3 )

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1 Homework Stoichiometry 1.) An oxide of iron has the formula Fe 3 O 4. What mass percent of iron does it contain? (72.360%) 2.) Hydrocortisone valerate is an ingredient in hydrocortisone cream, prescribed for skin problems. Its molecular formula is C 26 H 38 O 6. What is the percent by mass of carbon in hydrocortisone valerate? (69.928%) 3.) How many grams of potassium are in 28.9 g of K 2 CrO 7? (9.33 g) 4.) A substance contains 35.0 g nitrogen, 5.05 g hydrogen, and 60.0 g of oxygen. How many grams of hydrogen are there in a 141 g sample of this substance? (7.12 g) 5.) A substance, A 2 B, has the composition by mass of 60% A and 40% B. What is the composition of AB 2 by mass? (27% A, 73% B) 6.) Each molecule of ampicillin contains 16 atoms of carbon (plus other atoms). The mass percent of carbon in ampicillin is 55.00%. What is the molar mass of ampicillin? (349.4 g/mol) 7.) A compound is composed of element X and hydrogen. Analysis shows the compound to be 80% X by mass, with three times as many hydrogen atoms as X atoms per molecule. Which element is element X? (Carbon) 8.) A mixture of KCl and KNO 3 is 44.20% potassium by mass. What is the percentage of KCl in the mixture, by mass? (40.1%) 9.) A chloride of rhenium contains 63.6% rhenium. What is the formula of this compound? (ReCl 3 ) 10.) Adipic acid contains 49.32% C, 43.84% O, and 6.85% H by mass. What is the empirical formula? (C 3 H 5 O 2 ) 11.) A 1.90 g sample of an oxide of bromine is converted to g of AgBr. Calculate the empirical formula of the oxide. (BrO 2 ) 12.) The empirical formula of styrene is CH; its molar mass is g/mol. What is the molecular formula of styrene? (C 8 H 8 ) 13.) A compound composed of sulfur and fluorine is found to contain 25.24% by mass of sulfur. If the molar mass of the compound is g/mol, what is its molecular formula? (S 2 F 10 )

2 14.) The empirical formula of a group of compounds is CHCl. Lindane, a powerful insecticide, is a member of this group. The molar mass of lindane is g/mol. How many atoms of carbon does a molecule of lindane contain? (6) 15.) Vitamin C contains the elements C, H, and O. It is known to contain 40.9% C and 4.58% H by mass. The molar mass of vitamin C has been found to be about 180 g/mol. What is the molecular formula for vitamin C? (C 6 H 8 O 6 ) 16.) A g sample of a compound known to contain only carbon, hydrogen, and oxygen was burned in oxygen to yield g of CO 2 and g of H 2 O. What is the empirical formula of the compound? (C 3 H 3 O 2 ) 17.) You take an aspirin tablet (a compound consisting solely of carbon, hydrogen, and oxygen) with a mass of 1.00 g, burn it in air, and collect 2.20 g of carbon dioxide and g water. The molar mass of aspirin is between 170 and 190 g/mol. What is the molecular formula of aspirin? (C 9 H 8 O 4 ) 18.) What is the coefficient for water when the following equation is balanced? (6) As(OH) 3 (s) + H 2 SO 4 (aq) As 2 (SO 4 ) 3 (aq) + H 2 O(l) 19.) What is the coefficient for oxygen when the following equation is balanced? (7) NH 3 (g) + O 2 (g) NO 2 (g) + H 2 O(g) 20.) Determine the coefficient for O 2 when the following equation is balanced in standard form (smallest whole numbers). (19) C 6 H 14 (g) + O 2 (g) CO 2 (g) + H 2 O(g) 21.) What is the sum of the coefficients of the following equation when it is balanced using smallest whole numbers? (9) NaNH 2 + NaNO 3 NaN 3 +NaOH + NH 3 22.) Give (in order) the correct coefficients to balance the following reaction: (1, 2, 1, 6) H 2 SnCl 6 + H 2 S SnS 2 + HCl 23.) When the following equation is balanced with the smallest set of integers, what is the sum of the coefficients? (61) C 8 H 18 + O 2 CO 2 + H 2 O 24.) When the following equation is balanced, what is the sum of the coefficients? (9) Al 2 (SO 4 ) 3 + Ca(OH) 2 Al(OH) 3 + CaSO 4

3 25.) What are the correct coefficients to balance the following reaction, in order? (3, 5, 3, 5, 5) I 2 O 5 + H 2 S I 2 + SO 2 + H 2 O 26.) A 7.05 g sample of potassium chlorate was decomposed according to the following equation: 2KClO 3 2KCl + 3O 2 How many moles of oxygen are formed? ( mol) 27.) Sulfuric acid may be produced by the following process: 4FeS O 2 2Fe 2 O 3 +8SO 2 2SO 2 +O 2 2SO 3 SO 3 + H 2 O H 2 SO 4 How many moles of H 2 SO 4 will be produced from 5.62 moles of FeS 2? (11.2) 28.) Nitric oxide, NO, is made from the oxidation of NH 3, and the reaction is represented by the equation: 4NH 3 + 5O 2 4NO + 6H 2 O What mass of NO can be produced from 9.14 g of NH 3? (16.1 g NO) 29.) Nitric oxide, NO, is made from the oxidation of NH 3, and the reaction is represented by the equation: 4NH 3 + 5O 2 4NO + 6H 2 O What mass of O 2 would be required to react completely with 6.96 g of NH 3? (16.3 g O 2 ) 30.) The Claus reactions, shown below, are used to generate elemental sulfur from hydrogen sulfide. 2H 2 S + 3O 2 2SO 2 + 2H 2 O SO 2 + 2H 2 S 3S + 2H 2 O How much sulfur (in grams) is produced from 43.8 grams of O 2? (87.8 g) 31.) When g of ethylene (C 2 H 4 ) burns in oxygen to give carbon dioxide and water, how many grams of CO 2 are formed? (939.4 g) 32.) When rubidium metal is exposed to air, two atoms of rubidium, Rb, combine with one atom of oxygen. If 1.46 grams of rubidium is exposed to air, what will be the mass of the product in grams? (1.60 g)

4 33.) One commercial system removes SO 2 emissions from smoke at 95.0 C by the following set of balanced reactions: SO 2 + Cl 2 SO 2 Cl 2 SO 2 Cl 2 + 2H 2 O H 2 SO 4 + 2HCl H 2 SO 4 + Ca(OH) 2 CaSO 4 + 2H 2 O Assuming the process is 95.0% efficient, how many grams of CaSO 4 may be produced from 100. grams of SO 2? (202 g) 34.) Phosphoric acid can be prepared by reaction of sulfuric acid with phosphate rock according to the equation: Ca 3 (PO 4 ) 2 + 3H 2 SO 4 3CaSO 4 + 2H 3 PO 4 Suppose the reaction is carried out starting with 115 g of Ca 3 (PO 4 ) 2 and 84.4 g of H 2 SO 4. Which substance is the limiting reactant? (H 2 SO 4 ) 35.) Suppose the reaction Ca 3 (PO 4 ) 2 + 3H 2 SO 4 3CaSO 4 + 2H 3 PO 4 is carried out starting with 139 g of Ca 3 (PO 4 ) 2 and 71.5 g of H 2 SO 4. How much phosphoric acid will be produced? (47.6 g) 36.) SO 2 reacts with H 2 S as follows: 2H 2 S + SO 2 3S + 2H 2 O When 7.50 g of H 2 S reacts with g of SO 2, how much sulfur is formed? (10.6 g) 37.) How many grams of H 2 O will be formed when 32.0 g H 2 is mixed with 21.0 g of O 2 and allowed to react to form water? (23.6 g) 38.) A 15 g sample of lithium is reacted with 15 g of fluorine to form lithium fluoride. 2Li + F 2 2LiF After the reaction is complete, what will be present? (20. g of lithium fluoride and 9.5 g of lithium) 39.) For the reaction N 2 (g) + 2H 2 (g) N 2 H 4 (l), if the percent yield for this reaction is 82.5%, what is the actual mass of hydrazine (N 2 H 4 ) produced when g of nitrogen reacts with 3.55 g of hydrogen? (21.8 g N 2 H 4 ) 40.) Ammonia can be made by reaction of water with magnesium nitride as shown by the following unbalanced equation: Mg 3 N 2 (s) + H 2 O(l) Mg(OH) 2 (s) + NH 3 (g) If this process is 72% efficient, what mass of ammonia can be prepared from 18.5 kg magnesium nitride? (4.5 kg NH 3 ) 41.) Into a 2.67 liter container at 25 C are placed 1.23 moles of O 2 gas and 3.20 moles of solid C (graphite). If the carbon and oxygen react completely to form CO(g), what will be the final pressure in the container at 25 C? (22.5 atm)

5 42.) A mixture is prepared from 15.0 L of ammonia and 15.0 L chlorine measured at the same conditions; these compounds react according to the following equation: 2NH 3 (g) + 3 Cl 2 (g) N 2 (g) + 6HCl(g) When the reaction is completed, what is the volume of each gas (NH 3, Cl 2, N 2, and HCl, respectively)? Assume the final volumes are measured under identical conditions. (5.00 L, 0.00 L, 5.00 L, 30.0 L) 43.) The purity of a sample containing zinc and weighing g is determined by measuring the amount of hydrogen formed when the sample reacts with an excess of hydrochloric acid. The determination shows the sample to be 84.0% zinc. How many molecules of hydrogen (measured at STP) was obtained? ( molecules) 44.) One way to isolate metals from their ores is to react the metal oxide with carbon as shown in the following reaction: 2MO(s) + C(s) 2M(s) + CO 2 (g) If g of a metal oxide reacted with excess carbon and 4.27 L of CO 2 formed at 100ºC and 1.50 atm, what is the identity of the metal? (Cu)