Chapter 3 Sample Problems 1. Write the correct nuclear symbol for: (a)The isotope of sodium with mass 23 (b)The nuclide of vanadium that contains 28 neutrons (c)An α particle (d)The isotope of chlorine with mass 37 (e)The nuclide of magnesium that has an equal number of protons and neutrons. 2. By x-ray diffraction, it is possible to determine the geometric pattern in which atoms are arranged in a crystal and the distances between atoms. In a crystal of silver, four atoms effectively occupy the volume of a cube 0.409 nm on an edge. Taking the density of silver to be 10.5 g/cm3, calculate the number of atoms in one mole of silver. 3. If one were to cover the area of the 48 contiguous states with a mole of M&M’s, how thick would the layer be? Assume the area being covered is entirely flat. Helpful information and/or materials (maybe): 88 M&M’s fill a 100.0 ml cylinder 5280 ft = 1 mile area of 48 states = 3.02 x 106 mi2 2.54 cm = 1 in. Avogadro’s No. = 6.022 x 10 23 1 ml = 1 cm3 4. Calculate the number of molecules present in: (a)0.150 mol acetylene, C2H2, a fuel used in welding. (b)A 500 mg tablet of vitamin C, C6H8O6 (c) An average snowflake containing 5.0 x 10 -5 g of water (d) A 100 mg tablet of paracetamol, C8H9O2N, an analgesic sold under the name Tylenol (e) A tablespoon of table sugar, C12H22O11, weighing 12.6 g 5. Calculate the percent composition of: (a)morphine, C17H19NO3 (b) Lactic acid, HC3H5O3 (c) Cisplatin, PtCl2(NH3)2 6. A strip of electrolytically pure copper weighing 3.178 g is strongly heated in a stream of oxygen until it is all converted to a black oxide. The resultant black powder weighs 3.978 g. What is the percentage composition of this oxide? 7. The koala bear dines exclusively on eucalyptus leaves. Its digestive system detoxifies the eucalyptus oil, a poison to other animals. The chief constituent in eucalyptus oil is a substance called eucalyptol, which contains 77.87 % C, 11.76 % H, and the remainder O. (a)What is the empirical formula for this substance? (b)What is its molecular formula if the substance has a molecular mass of 154.2 amu? 8. A mixture containing potassium chlorate, potassium bicarbonate, potassium carbonate, and potassium chloride was heated, producing carbon dioxide, oxygen, and water vapor. The potassium chloride does not react under the conditions of the reaction. If 100.0 g of the mixture produces 1.80 g of water vapor, 13.20 g of carbon dioxide, and 4.00 g of oxygen, what was the composition of the mixture? 9. Aspirin, C9H8O4, is produced from salicylic acid, C7H6O3, and acetic anhydride, C4H6O3. C7H6O3 + C4H6O3 → C9H8O4 + HC2H3O2 (a)How much salicylic acid is required to produce 1.5 x 10 2 kg of aspirin, assuming that all of the salicylic acid is converted to aspirin? (b) How much salicylic acid would be required if only 80 % of the salicylic acid is converted to aspirin? (c) What is the theoretical yield of aspirin if 185 kg of salicylic acid is allowed to react with 125 kg of acetic anhydride? (d) If the situation described in part (c) produces 182 kg of aspirin, what is the percentage yield? 10. A 5.025 g sample of calcium is burned in air to produce a mixture of two ionic compounds, calcium oxide and calcium nitride. Water is added to this mixture. It reacts with calcium oxide to form 4.832 g of calcium hydroxide. How many grams of calcium oxide are formed? How many grams of calcium nitride? 11. A mixture of potassium chloride and potassium bromide weighing 3.595 g is heated with chlorine, which converts the mixture completely to potassium chloride. The total mass of potassium chloride after the reaction is 3.129 g. What percentage of the original mixture was potassium bromide? 1.A chemist is given an unknown element X. He finds that the element X has an atomic weight of 210.197 amu and consists of only two isotopes, 210X and 212X. If the masses of these isotopes are, respectively, 209.64 and 211.66 amu, what is the relative abundance of the two isotopes? 2. Chromium exists in four isotopic forms. The atomic masses and percent occurrences of these isotopes are listed in the following table: Isotopic mass (amu) Percent occurrence 50 4.31% 52 83.76% 53 9.55% 54 2.38% Calculate the average atomic mass of chromium. 3. A chemist reacts metal “B” with sulfur and obtains a compound of metal and sulfur. Assuming metal “B” weighed 2.435 (At.Wt. = 121.75 amu), and the compound weighs 3.397 g, what is the empirical formula of the compound? 4.An impure sample of aluminum sulfate is analyzed by forming a precipitate of insoluble barium sulfate by reacting aluminum sulfate with an excess of barium chloride. After washing and drying, 2.000 g of barium sulfate was obtained. If the original sample weighed 1.000 g, what was the percent of aluminum sulfate in the sample? 5. A chemist decides to react 2 g of VO (vanadium oxide) with 5.75 g of iron (III) oxide to produce V2O5 and FeO. How many grams of V2O5 can be obtained? 6.A silicious rock contains the mineral zinc sulfide. To analyze for zinc, a sample of the rock is pulverized and treated with hydrochloric acid to dissolve the zinc sulfide (silicious matter is insoluble). Zinc is precipitated from solution by the addition of potassium ferrocyanide, K 4Fe(CN)6. After filtering, the precipitate is dried and weighed. The reactions which occur are: ZnS(s) + 2 HCl(aq) ZnCl2(aq) + H2S(g) 2 ZnCl2(aq) + K4Fe(CN)6(aq) Zn2Fe(CN)6(s) + 4 KCl(aq) If a 2 g sample of rock yields 0.969 g of Zn2Fe(CN)6, what is the percentage of zinc in the sample? 7. Some solid calcium oxide in a test tube picks up water vapor from the surroundings to change completely to calcium hydroxide. An observed total initial weight (calcium oxide + test tube) of 10.860 g goes eventually to 11.149 g. What is the weight of the test tube? 8.“Hard water” contains small amounts of the salts calcium bicarbonate and calcium sulfate. These react with soap before it has a chance to lather, which is responsible for its cleansing ability. Calcium bicarbonate is removed by boiling to form insoluble calcium carbonate. Calcium sulfate is removed by reaction with sodium carbonate (washing soda) according to the following equation: CaSO4(aq) + Na2CO3(aq) CaCO3(s) + Na2SO4(aq) If the rivers surrounding New York City have a calcium sulfate concentration of 1.8 x 10 -3 g/L, how much sodium carbonate is required to “soften” (remove calcium sulfate) the water consumed by the city in one day (6.8 x 109 liters)? 9.It has been found that the following sequence can be used to prepare sodium sulfate: S(s) + O2(g) SO2(g) 2 SO2(g) + O2(g) 2 SO3(g) SO3(g) + H2O(l) H2SO4(l) 2 NaOH(aq) + H2SO4(aq) Na2SO4(aq) + 2 H2O(l) If you perform this sequence of reactions, how many moles of sodium sulfate could possibly be produced if you start with 1 mole of sulfur? 10. A chemist reacts iron (III) sulfate with barium chloride and obtains barium sulfate and iron (III) chloride. He writes the following balanced equation to express this reaction: Fe2(SO4)3(aq) + 3 BaCl2(aq) 3 BaSO4(s) + 2 FeCl3(aq) a.How many grams of barium chloride should be used to react with 10 g of iron (III) sulfate? b. How many grams of iron (III) sulfate will be necessary to produce 100 g of barium sulfate? c. From a mixture of 50 g of iron (III) sulfate and 100 g of barium chloride, how many grams of iron (III) chloride can be produced? 11. An oxide of titanium is made up of titanium and oxygen atoms. It is determined that the oxide is 40.06% oxygen. What is the simplest formula for the oxide? 12. Consider hydrazine, N2H4. a. What is the molar mass in grams? b. What is the simplest formula? c. How many moles are there in 2.65 g of hydrazine? d. How many grams of hydrazine are there in 12.01 x 10 26 molecules of hydrazine? e. How many hydrogen atoms are there in 1.769 mol of hydrazine? f. How many grams of hydrogen can be obtained from 100.0 g of hydrazine? 13. For the reaction 3 Br2(l) + I2(s) 2 IBr3(s) how many grams of IBr3 can be obtained from 5.00 g of Br2? 14. Consider the following reaction: 2 BF3(aq) + 3 H2O(g) B2O3(s) + 6 HF(g) In an experiment, 7.2 mol of BF3 reacts with 8.9 mol of H2O. a. What is the theoretical yield of B2O3 (in moles)? b. How many moles of the excess reactant remain? c. If the reaction has a 73% yield, what is the actual yield of B 2O3 (in moles)? 15.Metal ion A+3 adheres to filter paper more strongly than does metal ion B +3. In a paper chromotography experiment separating the two ions, which of the following statements would be true? a. Metal ion A+3 would travel faster than B+3 and have the larger Rf value. b. Metal ion A+3 would travel slower than B+3 and have the smaller Rf value. c. Metal ion A+3 would travel slower than B+3 and have the larger Rf value. d. Metal ion A+3 would travel faster than B+3 and have the smaller Rf value. e. It is impossible to predict which ion will travel faster and have the larger R f value.