Chem 105/107 Exam #2 Fall 2012

Transcription

1 October 15 th, 2012 Name: CLID: Score: Chem 105/107 Exam #2 Fall 2012 There are 20 multiple choices that are worth 3 points each. There are 4 problems and one bonus problem. Try to answer the questions, which you know first, and then try to solve the problems, which you are not sure about. Here is the summary of the total 100 points plus 6 points bonus. Carefully read the questions. There is a periodic table in the last page. Please feel free to tear it off for your convenience. Good luck! Multiple choices (20 total) 3 points each, the total is 60 points Problems #1 8 points #2 8 points #3 14 points #4 10 points #5 (bonus) 6 points Total 100 points + 6 points You could use your calculator. No notes or books of any sort may be used during the exam. I have neither given nor received aid on the exam. Signature and date 1

2 I. Multiple Choices: (3 points each, the total is 60 points) 1. How many moles of O atoms are there in 1.5 moles of H 3 PO 4? a) 1.5 mol b) 3.0 mol c) 4.5 mol d) 6.0 mol 2. Mass spectrometer developed by the English physicist F. W. Aston can separate different atoms based on. ions are generated by the collision between gaseous sample and high energy electrons. a) charge to mass; Positive b) charge to mass; Negative c) mass to size; Positive d) mass to size; Negative 3.What is the average mass, in grams, of one atom of iron? a) x g b) x g c) x g d) g 4. The oxidation number of N in NaNO 3 is. a) -3 b) +3 c) +5 d) H 2 PO 4 - is and HPO 4 2- is in the following chemical reaction: H 2 PO H 2 O HPO H 3 O + a) an acid; a conjugate acid b) an acid; a conjugate base c) a base; a conjugate acid d) a base; a conjugate base 6. Select the compound in which sulfur has its lowest possible oxidation number. a) Na 2 SO 4 b) SO 2 c) SCl 2 d) H 2 SO 3 2

3 g of glucose (C 6 H 12 O 6 ) is dissolved in 10.0 L of water. The molarity (M) of the glucose solution is. Assume that the final volume of the glucose solution is 10.0 L. The molar mass of glucose (C 6 H 12 O 6 ) is 180 g/mol. a) M b) M c) 1.00 M d) 10.0 M 8. One nanogram (ng) does not seem like a very large number. How many magnesium atoms are there in 1.00 ng of magnesium? Molar mass of Mg is g/mol. a) 4.11 x atoms b) 1.46 x atoms c) 2.48 x atoms d) 6.02 x atoms 9. What volume of a 6.74 M CH 3 COOH stock solution would you use to prepare 30.8 ml of 1.25 M CH 3 COOH solution? a) 2.37 ml b) 2.84 ml c) 3.19 ml d) 5.71 ml 10. Which of the following compounds is an example of weak electrolyte? a) Glucose b) CH 3 COOH c) NaCl d) Ethanol 11. Identify the major ionic species present in an aqueous solution of Na 2 CO 3. a) Na +, CO 3 2- b) Na 2 +, CO 3 2- c) Na +, C -, O 3 d) Na 2 +, C +, O What mass of Na 2 SO 4 is needed to prepare 3.50 x 10 2 ml of a solution having a sodium ion concentration of M? The molar mass of Na 2 SO 4 is g/mol. a) 3.11 g b) 6.21 g c) 8.88 g d) 12.4 g 3

4 13. The following chemical reaction is an example of and is the oxidizing agent. Cl 2 + 2KBr 2KCl + Br 2 a) halogen displacement reactions; Cl 2 b) halogen displacement reactions; KBr c) metal displacement reactions; Cl 2 d) metal displacement reactions; KBr 14. There are two stable isotopes of chlorine: 35 17Cl with an atomic mass of amu and Cl with an atomic mass of Given that the average atomic mass of a Cl atom is amu, which of the following statement is most likely true? a) Cl contains almost exclusively of 35 17Cl and with very little 37 17Cl. b) Cl contains more 35 17Cl than 37 17Cl. c) Cl contains roughly equal amounts of 35 17Cl and 37 17Cl. d) Cl contains almost exclusively of 37 17Cl and with very little 35 17Cl. 15. An organic thiol compound is 38.66% C, 9.73% H, and 51.61% S by mass. What is the empirical formula of this compound? a) C 2 H 6 S b) C 3 H 8 S c) C 4 H 10 S d) C 4 H 12 S 16. Which of the following statement about solubility is most likely correct? a) Solubility is the maximum amount of solute that will dissolve in a given quantity of solvent at a specific temperature. b) Solubility is the maximum amount of solute that will dissolve in the maximum quantity of solvent at a specific temperature. c) Solubility is the certain amount of solute that will dissolve in a given quantity of solvent at a specific temperature. d) Solubility is the certain amount of solute that will dissolve in the maximum quantity of solvent at a specific temperature. 17. How many moles of C are in g of ethanol C 2 H 5 OH? For convenience of calculation, the atomic mass of carbon is amu, the atomic mass of hydrogen is amu and the atomic mass of oxygen is amu. a) mol b) 1.76 mol c) 3.53 mol d) 7.05 mol 4

5 18. Which of the following statements is true about hydration? a) Hydration is a process in which an ion is surrounded by water molecules arranged in a specific manner. b) Hydration is a process in which ions can form ionic interactions between each other in an aqueous solution. c) Hydration is a process in which a water molecule is surrounded by ions arranged in a specific manner. d) Hydration is a process in which water molecules form hydrogen bonds with each other. 19. You are given a balanced reaction: 2H 2 + O 2 2H 2 O. How many moles of water could be made from 5.0 mol H 2 and 3.0 mol O 2 at the end of the reaction? a) 1.5 mol b) 3.0 mol c) 5.0 mol d) 8.0 mol 20. The oxidation number of N in N 2 H 4 is. a) -4 b) -2 c) +2 d) +4 III. Problem Solving 1. You are given the molecular equation of following chemical reaction: (total 8 points) 2AgNO 3 (aq) + Na 2 SO 4 (aq) Ag 2 SO 4 (s) + 2NaNO 3 (aq) (a) Write the ionic equation for this chemical reaction. (3 points) (b) Write the net ionic equation for this chemical reaction. (3 points) (c) What are the spectator ions in this chemical reaction? You are not required to explain it. (2 points) 5

6 2. Calculate the molarity (M) of an H 2 SO 4 solution if ml of it requires ml of M NaOH for neutralization. Show your calculations. (8 points) H 2 SO 4 + 2NaOH Na 2 SO 4 + 2H 2 O 3. (a) Balance the following chemical reaction: (2 points) MnO 2 + HCl MnCl 2 + Cl 2 + H 2 O (b) If 0.86 mole of MnO 2 and 48.2 g of HCl react, how many grams of Cl 2 will produced? Show your calculations. Remember to put correct significant figure and unit in your final answer. (8 points) molar mass of Cl 2 is g/mol molar mass of HCl is g/mol (c) Which one is the limiting reagent in this reaction? Justify your answer. (2 points) (d) Calculate the reaction yield if the actual yield of Cl 2 is 15.8 g. Show your calculation. (2 points) 6

7 4. For the complete oxidation and reduction (redox) reaction given here: (total 10 points) Zn (s) + CuSO 4 (aq) ZnSO 4 (aq) + Cu (s) (a) Write the half oxidation reaction. (3 points) (b) Write the half reduction reaction. (3 points) (c) Identify the oxidizing agent. Justify your answer. (2 points) (d) Identify the reducing agent. Justify your answer. (2 points) 5. Bonus questions (6 points) (5a) Balance the following chemical reaction: (3 points) Cu + HNO 3 NO + Cu(NO 3 ) 2 + H 2 O (5b) ml of a M Na 2 CO 3 solution is added to 46.0 ml of M NaCl. What is the concentration of sodium ion in the final solution? Assume that volume is additive. (3 points) a) M b) M c) M d) M 7

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