Houston Community College System Chemistry 1405 SAMPLE EXAM # 3 1 HOUSTON COMMUNITY COLLEGE CHEM 1405 Name: _____________________ Exam # 3 (Chap. 8-12) Score: PART I – Multiple choice: (3 points each) 1) How many moles of chlorine gas react with 1 mol of hydrogen gas according to the following balanced chemical equation? H2(g) + Cl2(g) → 2 HCl(g) A) 1 mol 2) B) 2 mol C) 3 mol D) 4 mol In the following reaction, if 4 moles of sulfur is used how many moles of oxygen is required? S A) 1 mole + B) 2 moles O2 → SO3 C) 3 moles D) 4 moles E) 6 moles 3) What is the statement of the following balanced reaction if 10 g of N2 and 10g of H2 were used? N2 + 4) H2 → NH3 A) Hydrogen is limiting reactant B) Hydrogen is excess reagent C) Nitrogen is limiting reactant D) Nitrogen is excess reagent E) B and C In the following reaction, theoretically, 1 mole of Cu and 1 mole S was produced. Calculate the mass of Copper and Sulfur to be used. Cu + S → CuS A) 63.55g Cu and 32.07g S B) 30g Cu and 20g H D) 42.60g Cu and 7.40 g S E) 25g Cu and 25g S C) 35.0g Cu and 15g H 5) What is the % yield if 45.6g of CuS was produced in the above reaction? A) 87.9% 6) B) 47.7% C) 91.2% D) 95.6% E) None of them If the air pressure in this room is 785 mmHg, what is the pressure in inchHg (760 mmHg = 29.9 inchHg)? A) 30.2 inchHg B) 30.88 inchHg C) 24.9 inchHg 2 D) 36. 2 inchHg E) None of them 7) Calculate the amount of 2.7 L Neon under STP conditions A) 0.12 moles B) 1.6 moles C) 1.9 moles D) 2.3 moles E) None of them 8) According to ideal gas equation what is the volume of 1mole gas under STP conditions? A) 18.8 L B) 22.4 L C) 27.3 L D) 30.8 L E) 44.01 L 9) Which of the following changes decreases the pressure of a gas? A) increasing the volume C) decreasing the number of gas molecules B) decreasing the temperature D) all of the above 10) Which of the following states that the pressure and volume are inversely proportional for a gas at constant temperature? A) Boyle's law B) Charles' law C) Dalton's law D) Gay-Lussac's law 11) Assuming STP conditions, how many moles of water vapor react to produce 3L of hydrogen gas? C(s) + H2O(g) CO(g) + H2(g) A) 0.134 moles B) 2.2 moles C) 3.1 moles D) 0.44 moles 12) In an experiment, 1.201 g of charcoal reacts with 6.414 g of powdered sulfur. What is the mass of product? C(s) + 2 S(s) CS2(g) A) 4.408 g B) 5.213 g C) 7.615 g D) 8.816 g E) None of them 13) If the following reaction requires 3.4 atm preassure and 67 oC temperature were applied, Calculate the volume of oxygen when 20g of FeO was used. FeO A) 4.3 L + O2 B) 4.5 L Fe2O3 C) 2.3 L D) 9.6L E) 2. 0 L 14) Which of the following states that the temperature and volume are directly proportional for a gas at constant pressure? A) Boyle's law B) Charles' law C) Dalton's law D) Gay-Lussac's law 15) If an aluminum scuba tank contains compressed air at 2750 psi, what is the pressure expressed in inches of mercury? A) 92.0 inHg B) 187 inHg C) 5594 inHg 3 4 D) 8.22 × 10 inHg 16) Identify the molecular solids among MgCl2, Fe, SiO2, and He A) SiO2 B) MgCl2 C) He D) Fe 17) A 1L Neon gas at constant pressure is cooled from 50 oC to 25 oC. What is the final volume? A) 0.5 L B) 0.7 L C) 0.9 L D) 1.2 L E) 1.5 L 18) In which of the following the atoms are held together by ionic bonds? A) AlCl3 B) Mg3N2 C) Cu2S D) all of the above 19) How many bonding electrons are present in CO2 molecule? A) 2 B) 4 C) 6 D) 8 E) 10 20) What is the molecular geometry of SO2 A) Linear C) Trigonal planar B) Bent D) Trigonal pyramidal E) Tetrahedron PART II – Show All Your Work: (8 points each) 1) Calculate the mass of NH3 and limiting reactant in the reaction of 2. 5 mole of Hydrogen and 2 5 mole of Nitrogen in the following reaction. N2 + H2 → NH3 2) Match the following 1. H2 A. Dipole-Dipole 2. H3C NH B. London forces H3C 3. H-Cl C. Hydrogen bonding 4 3) What is the volume of oxygen gas at STP from the decomposition of 10.8 g of mercuric oxide ( molar mass of HgO: 216.59 g/mol)? __HgO(s) → __Hg(l) + __O2(g) 4) Write the Lewis dot structure of NH3 and indicate molecular geometry 5) Hydrogen has an electronegativity value of 2.1. Given the electronegativity of N, O, and P (3.0, 3.5, and 2.1, respectively), predict which of the following has nonpolar bonds. NH3, H2O, PH3 5 BONUS QUESTION – Show All Your Work: (10 points) Draw the Lewis structure for the following molecules and indicate the number of bonding electrons, nonbonding electrons and the shape of each one. SiO2, CH4 6 7