14 MC pts problem pts. = 24 pts. total possible

Size: px

Start display at page:

Download "14 MC pts problem pts. = 24 pts. total possible"

Beryl Sheena Ray
5 years ago
Views:

1 CHE 211 Answers in BOLD RED EXAM 1, 2014 KEY On this mastery- based exam, you must score at least 70% to complete the exam. If your score is less than 70% you will have to do a retake of one or two chapters material (normally those on which you did worst). Any new points beyond what you score this time on those chapters will then be added to your score up to a maximum of 75%. Multiple Choice (2% each) and Problems (10% each, partial credit possible) grouped by chapter Please select the BEST answer to each multiple choice question and mark it clearly on the answer sheet. Problems should be answered in the space immediately after each. SHOW ALL WORK! Thank you. CHAPTER 1 (BASICS) 14 MC pts problem pts. = 24 pts. total possible 1. Which of the following molecular scenes depicts a mixture of three substances, 2 of which are compounds? D 2. What physical state would be the best match for all four of the molecular scene drawings above? A. liquid B. gas C. solid D. aqueous 3. The energy of chemical bonds is from the relative position of atoms in relation to others; this is thus a form of A. kinetic energy B. potential energy 4. How many milliliters (ml) are there in a liter (L)? A. 1,000,000 B. 100 C. 1,000 D. 10, A liquid substance in a sealed container disappears when heated and returns upon cooling. This is probably a A. physical change B. chemical change C. neither has occurred D. both have occurred 6. A piece of iron ore with a volume of 733 ml has a mass of 3775 g. What is its density in g/ml? A (sig fig) B C D The temperature of a lab is stated to be 303 Kelvin. What would that be in F? (see data sheet for conversions) A. 79 B. 92 C. 84 D. 86 Answer as requested. If calculations are required, then please show those also. Two students are competing for a summer lab job. The lab supervisor tests their competence by having them weigh the same object on ten different balances, all supposedly accurate to ±0.001 g. Bob comes up with an average weight of g with a standard deviation of g, while Gloria gets g on average, with a standard deviation of g. The actual object weight was g according to the supervisor. Using the terms precision and accuracy, compare the quality of the work each person did (i.e., which was most precise and which was most accurate [could be the same person] and what do you mean by each of those terms?). Precision is how consistent a set of measurements is; based upon this, Gloria has more precision (is more precise) because her standard deviations are smaller, indicating her measurements were closer Accuracy is a measure of how close a set of measurements is to the true value; on that basis, Bob is more accurate, since his average value is closer to the true value of the weight, even thought his standard deviation is worse. This could occur is Bob had poor technique, while Gloria may have had some systematic error in her measurements.

2 CHE 211 Exam 1 Key Page 2 CHAPTER 2 (MATTER) 14 MC pts problem pts. = 24 pts. total possible 1. Which statement is correct? A. a pure substance can be an element or a compound B. impure substances must be homogeneous mixtures C. molecules must contain 2 or more elements D. only heterogeneous substances are true mixtures 2. J.J. Thomson was able to discover some of the properties of the electron, but he could only determine its A. mass/charge ratio B. mass C. charge D. magnetic field 3. Thomson created the plum pudding atomic model. Who disproved that model by his experiments? A. Millikan B. Einstein C. Rutherford D. Geiger 4. Two atoms are isotopes of one another. This means their count is the same but not their count. A. electron ; proton B. neutron ; electron C. proton ; neutron D. proton ; electron 5. Which of these is a metalloid? A. Se B. Ba C. C D. Ar 6. Which chemical species is covalently bonded but is itself an ion? A. cations B. anions C. monoatomic ions D. polyatomic ions 7. What is the proper name (not a common name) for Se 2Br 4? A. diselenium tetrabromide B. selenium (II) bromide C. selenium (II) bromide (IV) D. selenic bromide John Dalton s Atomic Theory had four postulates. State them, then explain the current scientific viewpoint on each (Is it still considered true? Why or why not? What is the current atomic theory s new statement? Dalton s Postulate Still considered true? Why? New Statement (now) All matter consists of atoms, which are indivisible and unchanging In part; we now know atoms are divisible All stable matter consists of atoms; they maybe divided but are then not stable. Atoms cannot be converted to other elements atoms No. Elements may undergo nuclear transmutations. Atoms can be converted to those of other elements by nuclear reactions All atoms of one element have a unique mass and set of properties No; all atoms of one element have the same proton count Every element s atoms have a unique proton count; their neutron count and thus mass may vary Atoms of elements combine to form compounds Yes Unchanged Extra credit (5 points maximum) for each of the following, fill in the empty boxes as listed Formula Ionic or covalent? Proper chemical name KNO 3 Ionic Potassium nitrate IF 5 Covalent Iodine pentafluoride CF 4 Covalent Carbon tetrafluoride CoSO 4 Ionic Cobalt (II) sulfate P 2Se 5 Covalent Diphosphorus pentaselenide

3 CHE 211 Exam 1 Key Page 3 CHAPTER 3 (STOICHIOMETRY) 16 MC pts problem pts. = 26 pts. total possible 1. What is the molar mass of niacin, C 6H 5NO 2? A. 142 g B. 123 g C g D. 114 g 2. Niacin (see above question) has a density of g/cm 3. What volume should 3 moles of it have? A. 289 cm 3 B. 175 cm 3 C. 205 cm 3 D cm 3 3. If we have moles of niacin, how many ATOMS would we have all together? A x B x C x D x Two different substances have the same molecular formula. That means that they also have the same: A. structures B. properties C. bonds between atoms D. empirical formula 5. When a mole of the fuel undecane, C 11H 24, is fully combusted to CO 2 and H 2O, it requires moles of O 2. A. 23 B. 17 C. 20 D Wood alcohol is the older name for methanol, CH 3OH, which used to be made by heating wood in a closed chamber. It is now made by two reactions: C(s) + H 2O(l) à CO(g) + H 2(g) and CO(g) + 2 H 2(g) à CH 3OH(l). What, then, is the equation for the combined reactions used to produce methanol commercially? A. C(s) + H 2O(l) + H 2(g) à CH 3OH(l) B. 2 C(s) + 4 H 2(g) + O 2(g) à 2 CH 3OH(l) C. C(s) + H 2O(l) + H 2(g)à CO(g) + CH 3OH(l) D. CO(g) + H 2(g) + H 2O(l) à CH 3OH(l) + ½ O 2(g) 7. Formaldehyde is made by doing 2 CH 3OH(g) + O 2(g) à 2 CH 2O(g) + 2 H 2O(g) at 300 C. If you start with 64 g of CH 3OH and 64 g of O 2, how many grams of formaldehyde (CH 2O) should be produced, at most? A g B. 30. g C. 60. g D g 8. If you run the reaction described in question 7 and get 52 g of formaldehyde, what was the percent yield? A. 87% B. 43% C. 170% D. 41% SHOW WORK, either directly by doing the calculations below, or as setups for calculator use. An alcohol (an organic compound which contains only C, H, and O) is burned and its combustion products analyzed. This combustion analysis showed that the alcohol was 65.71%C and 12.41% H by weight (the remainder being O). What is the empirical formula of this alcohol? 100% - (65.71% %) = 21.88% O by weight So, 100 g of the alcohol = g C g H g O. Need to find the molar ratios: g C / ( g C/mol) = 5.47 mol C 5.47/1.37 = g H/ (1.008 g/mol) = 12.3 mol H 12.3/1.37 = g O/ ( g/mol) = 1.37 mol O 1.37/1.37 = 1 This, the empirical formula = C 4H 9O If the estimated molecular weight of this alcohol is about 150 g/mole, what would its molecular formula be? Molar mass of C 4H 9O = = /73 2, so molecular formula is twice the empirical (it will always be a whole number multiple) Thus, molecular formula is C 8H 18O 2

4 CHE 211 Exam 1 Key Page 4 CHAPTER 4 (REACTION TYPES) 16 MC pts problem pts. = 26 pts. total possible 1. The compound sodium phosphate (Na 3PO 4) is dissolved to make a 1.0 M solution. What is the concentration of all the ions in total in this solution? A. 1.0 M B. 4.0 M C. 2.0 M D M ml of 2.33 M NaNO 3 is measured out carefully by a student. How many moles of NaNO 3 did he pour out? A B C D Which of these ionic substances is most likely to NOT be water soluble? A. KNO 3 B. LiCl C. (NH 4) 2SO 4 D. Ca 3(PO 4) 2 4. Strong acids are generally: A. covalent substances that ionize 100% in water B. ionic substances that are very soluble in water C. covalent substances that ionize 1% in water D. ionic substances that contain very stable oxyanions 5. Ba(OH) 2 and HClO 3 react: Ba(OH) HClO 3 à Ba(ClO 3) H 2O. If ml of unknown concentration Ba(OH) 2 is titrated with M HClO 3, ml of the acid is needed. What is the Ba(OH) 2 molarity? A B C. 0. D In the unbalanced reaction S 2O I 2 + H 2O à I + SO H +, gets oxidized and gets reduced. A. S ; I B. O ; S C. H ; O D. I ; H 7. When the redox equation in question 6 gets balanced, what are the respective coefficients of S 2O 3 2, I 2, & H 2O? A. 2 ; 6 ; 7 B. 2 ; 5 ; 8 C. 1 ; 4 ; 5 D. 1 ; 3 ; 4 8. What is the oxidation number of the S in thiosulfate ion, S 2O 3 2? A. +4 B. +2 C. +3 D. +6 Balance the following two reactions and then write a NET IONIC EQUATION for each of them, with all states. Sr(NO 3) 2(aq) + Na 2SO 4(aq) à SrSO 4(s) + NaNO 3(aq) Balancing is simple in this case: Sr(NO 3) 2(aq) + Na 2SO 4(aq) à SrSO 4(s) + 2 NaNO 3(aq) Sr 2+ (aq) + 2 NO 3 (aq) + 2 Na + (aq) + SO 4 2 (aq) à SrSO 4(s) +2 NO 3 (aq) + 2 Na + (aq) Which will simplify to a net ionic equation of: Sr 2+ (aq) + SO 4 2 (aq) à SrSO 4(s) HNO 3(aq) + Fe(s) à Fe(NO 3) 3(aq) + H 2O(l) + NO(g) This is a redox reaction: Fe à Fe e and N e à N 2+ Electrons already balance so the Fe and NO should both be 1; other species must be balanced to acknowledge those facts: 4 HNO 3(aq) + Fe(s) à Fe(NO 3) 3(aq) + 2 H 2O(l) + NO(g) The net ionic equation will ignore the unchanged nitrate ions: [can use H + or H 3O + ] 4 H + [or 3 H 3O + ] + NO 3 (aq) + Fe (s) à Fe 3+ (aq) + NO(g) + 2 H 2O(l) [or 3 H 2O]

5 CHE 211 Exam 1 Key Page 5

1. My answers for this Chemistry 102 exam should be graded with the answer sheet associated with: a) Form A b) Form B c) Form C d) Form D e) Form E

Hour Exam I Page 1 1. My answers for this Chemistry 102 exam should be graded with the answer sheet associated with: a) Form A b) Form B c) Form C d) Form D e) Form E 2. Consider the measurements 9.74