Chemical Reactions and Equations

Transcription

1 Chemical Reactions and Equations 1991 B 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 CO 2 at standard conditions. What is the empirical formula of the hydrocarbon? 2000 B Answer the following questions about BeC 2 O 4 (s) and its hydrate. (a) Calculate the mass percent of carbon in the hydrated form of the solid that has the formula BeC 2 O 4 3H 2 O. (b) When heated to 220. C, BeC 2 O 4 3H 2 O(s) dehydrates completely as represented below. BeC 2 O 4 3H 2 O(s) BeC 2 O 4 (s) + 3 H 2 O(g) If 3.21 g of BeC 2 O 4 3H 2 O(s) is heated to 220. C calculate (i) the mass of BeC 2 O 4 (s) formed, and, (ii) the volume of the H 2 O(g) released, measured at STP B Answer the following questions about acetylsalicylic acid, the active ingredient in aspirin. (a) The amount of acetylsalicylic acid in a single aspirin tablet is 325 mg, yet the tablet has a mass of 2.00 g. Calculate the mass percent of acetylsalicylic acid in the tablet. (b) The elements contained in acetylsalicylic acid are hydrogen, carbon, and oxygen. The combustion of g of the pure compound yields g of water and 3.72 L of dry carbon dioxide, measured at STP. Determine the mass, in g, of each element in the g sample of the compound. Stoichiometry 1. Hydrogen gas was generated according to the equation: Zn(s) + 2HCl(aq) H 2 (g) + ZnCl 2 (aq) When grams of Zn metal reacted with excess HCl, 7.50 L H 2 (g) was collected at STP. The theoretical yield of H 2 (g) for this reaction is: (show work) The percentage yield for this reaction is: (show set-up) 2. A compound composed of carbon and hydrogen is analyzed by combustion. When a g sample of the compound is burned, g CO 2 and 7.72 g H 2 O are formed. What is the empirical formula of the compound? The molar mass of the compound is found to be about 30 g mol -1. The molecular formula for the compound is

2 Reaction Prediction Solutions of lead(ii) nitrate and sulfuric acid are mixed.. (i) Balanced equation: (ii) If the reaction mixture is filtered, what substance will end up in the filter? b) A strip of magnesium metal is placed in a solution of iron(ii) chloride. (i) Balanced equation: (ii) Which chemical is the oxidizing agent? Circle the ionic compounds that are Insoluble (i.e. circle the precipitates): MgF 2 CuSO 4 NH 4 Cl Fe(OH) 3 CsF AgCl CdS CuF 2 PbSO 4 Ba(OH) 2 Na 2 SO 4 NH 4 OH Sr(NO 3 ) 2 Hg 2 I 2 Na 2 CrO 4 BaCO 3 PbBr 2 CaC 2 O 4 HC 2 H 3 O 2 MgO Predict the products in these molecular equations. Indicate (s), (l), (g), or (aq): CuSO 3 + HF Ca(NO 3 ) 2 + (NH 4 ) 2 SO 4 HCl + Zn(C 2 H 3 O 2 ) 2

3 Thermochemistry 1. If 5430 J of energy is used to heat 1.25 L of room temperature water (23.0 C), what is the final temperature of the water? 2. A 100. gram sample of aluminum (specific heat = J g -1 C -1 ) in boiling water is added to an insulated cup containing 50.0 grams of water at 5.00 C. What will the final temperature of the mixture be? The specific heat of water is J g -1 C Iron ore can be converted to iron metal with CO gas. FeO (s) CO (g) Fe (s) CO (g) Calculate the standard enthalpy change for this reaction from these reactions of iron oxides with CO: (1) 3 Fe O (s) CO (g) 2 Fe O (s) CO (g) H - 47 kj (2) Fe O (s) 3 CO (g) 2 Fe (s) 3 CO (g) H -25 kj (3) Fe O (s) CO (g) 3 FeO (s) CO (g) H 19 kj chemical 5. CO 2 (g) 6. H 2 O(g) 7. C 8 H 18 (l) kj mol - 8. H f kj mol ??? kj mol Knowing that the H combusion of octane, C 8 H 18, is kj mol -1 calculate the H f of octane. Atom and Periodic Table 1. The successive ionization energies for one of the period three elements is listed below. Which element is referred to? E kj/mol E2 1,816 kj/mol E3 2,744 kj/mol E4 11,580 kj/mol E5 15,030 kj/mol a) Na b) Mg c) Al d) Si e) P 2. Which of the following sets of quantum numbers is possible for a 3d electron? a) n = 3, l = 3, m l = 2, m s = b) n = 2, l = 1, m l = +1, m s = 1 2 c) n = 3, l = 1, m l = 0, m s = 1 2 d) n = 3, l = 2, m l = 2, m s = e) n = 4, l = 1, m l = +1, m s = + 1 2

4 3. What is wrong with the following ground state electron configurations? Molecular Geometry & Bonding 1. What molecular shape is pictured below? a) linear d) planar triangular b) tetrahedral e) trigonal bipyramid c) octahedral 2. Which of the following is the correct Lewis structure for SOCl2? (Consider formal charge) a) d) b) e) c) D (Required) Consider the molecules PF 3 and PF 5. (a) Draw the Lewis electron-dot structures for PF 3 and PF 5 and predict the molecular geometry of each. (b) Is the PF 3 molecule polar, or is it nonpolar? Explain. (c) On the basis of bonding principles, predict whether each of the following compounds exists. In each case, explain your prediction. (i) NF 5 (ii) AsF 5 4. What is the hybridization of the oxygen atoms in CH 3 OH and CO 2, respectively? a) sp 3, sp 3 d) sp 2, sp 2 b) sp 3, sp 2 e) sp 3, sp c) sp 2, sp 3

5 5. Consider the structural formula for the acetate ion, C2H3O2 or CH3COO. Indicate the hybridization used by each of the carbon and oxygen atoms. H O H C C O H Gases 1. A real gas would act most ideal at a) 1.0 atm and 273 K b) 10 atm and 546 K c) 10 atm and 273 K d) 0.5 atm and 546 K e) 0.5 atm and 273 K 2. At STP, it was found that 1.12 L of a gas had a mass of 2.78 g. Its molar mass is. 3. A given mass of a gas occupies 5.00 L at 65 C and 480 mmhg. What is the volume of the gas at 630 mmhg and 85 C? a) 5.00 x x b) 5.00 x x c) 5.00 x x d) 5.00 x x e) 5.00 x x Intermolecular Forces 1. Which one of the following is linked with the correct intermolecular force of attraction? a) NH 3... dipole-dipole b) AlH 3... London dispersion forces c) H 2... hydrogen bonding d) C 2 H 4... covalent bonding e) HCl... ionic 2. A typical phase diagram for a substance is given below. At what point on the diagram do solid and liquid exist at equilibrium? a) A b) B c) C d) D e) E

6 Solutions 1. The mol fraction of NH 4 Cl in a solution is What is its molality? (The molar mass of water is g/mol.) a) 1.78 m d) m b) 1.66 m e) m c) m 2. Which of the following would have a boiling point closes to that of 1 m NaCl? a) 1 m sucrose (C 12 H 22 O 11 ) b) pure H 2 O d) 0.5 m CH 3 OH c) 1 m MgCl 2 e) 1 m NH 4 NO 3 3. Which of the following solutions would have the lowest vapor pressure? a) 1 m glucose (C 6 H 12 O 6 ) b) 1 m MgCl 2 d) 1 m NaBr c) 1 m NaNO 3 e) pure H 2 O 4. What is the molar mass of a compound if 4.28 grams is dissolved in 25.0 grams of chloroform solvent to form a solution which has a boiling point elevation of 2.30 C. The boiling point constant of chloroform K b is 3.63 C/m. a) 34.5 g/mol d) 168 g/mol b) 67.5 g/mol e) 270 g/mol c) 135 g/mol Equilibrium 1. Which reaction characteristics are changing by the addition of a catalyst to a reaction to a reaction at constant temperature? 1. activation energy 2. equilibrium concentrations 3. reaction enthalpy (A) 1 only (B) 3 only (C) 1 and 2 only (D) 1, 2, and 3 2. Consider the reaction system, CoO(s) + H 2 (g) Co(s) + H 2 O(g). The equilibrium constant expression is. 3. Solid HgO, liquid Hg, and gaseous O2 are placed in a glass bulb and are allowed to reach equilibrium at a given temperature. 2HgO(s) 2Hg(l) + O2(g) H = kcal The mass of HgO in the bulb could be increased by a) adding more Hg. b) removing some O2. c) reducing the volume of the bulb. d) increasing the temperature. e) removing some Hg.