Chem. 1A Midterm 1 Version B October 14, 2016

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1 Chem. 1A Midterm 1 Version B October 14, 2016 First initial of last name Name: Print Neatly. You will lose 1 point if I cannot read your name or perm number. Perm Number: All work must be shown on the exam for partial credit. Points will be taken off for incorrect or missing units. Calculators are allowed. Cell phones may not be used as calculators. On fundamental and challenge problems you must show your work in order to receive credit for the problem. If your cell phone goes off during the exam you will have your exam removed from you. Fundamentals (of 36 possible) Problem 1 (of 16 possible) Problem 2 (of 18 possible) Multiple Choice (of 30 possible) Midterm Total (of 100 possible) 1

Fundamental Questions Each of these fundamental chemistry questions is worth 6 points. You must show work to get credit. Little to no partial credit will be awarded.

2 Fundamental Questions Each of these fundamental chemistry questions is worth 6 points. You must show work to get credit. Little to no partial credit will be awarded. Make sure to include the correct units on your answers. 1) 6 pts In a sample of 200 chlorine atoms, it is found that 151 are 35 Cl ( amu), and 49 are another isotope. What is the other naturally occurring isotope of chlorine? atomic mass = (frac 35Cl )(m 35Cl ) + (frac?cl )(m?cl ) amu = ( ) ( amu) + ( ) (m? Cl ) m?cl = amu Therefore, the other isotope is 37 Cl. 2) 6 pts On the following periodic table indicate the location of the metals, nonmetals, metalloids. Also label which group is the noble gases, alkaline earth metals, alkali metals, halides, and transition metals. 3) 6 pts Fill in the following table Symbol 37 Cl - 23 Na + 81 Br U 6+ # of Protons # of neutrons # of electrons Mass number

3 4) 6 pts What is the mass percentage of Cl in NaCl? mass % Cl = m Cl 100% m total Assume 1 e NaCl Calculate m tot Calculate m Cl 1 NaCl ( 1 NaCl ( Calculate mass % Cl mass % Cl = g NaCl 1 NaCl ) = g NaCl 1 Cl g Cl ) ( NaCl 1 Cl ) = g Cl g 100% = % Cl g 5) 6 pts What are the names of the following compounds: NiNO 3 AgBr H 2SO 3(aq) N 2O 5 (NH 4) 2CO 3 SF 6 nickel(i) nitrate silver bromide sulfurous acid dinitrogen pentoxide ammonium carbonate sulfur hexafluoride 6a) 2 pts How many es in atoms? atoms ( 6b) 2 pts How many es of copper in 3.20 g? 3.20 g Cu ( 1 Cu g Cu atoms ) = Cu 6c) 2 pts How many es of O in 3.4 of CuSO 4? 4 O 3.4 CuSO 4 ( ) = 14 O 1 CuSO 4 ) =

4 Challenge Problems Each of the following short answer questions are worth the noted points. Partial credit will be given. You must show your work to get credit. Make sure to include proper units on your answer. 1) 16 pts Gaseous butane (CH 3(CH 2) 2CH 3) reacts with gaseous oxygen gas (O 2) to produce gaseous carbon dioxide (CO 2) and gaseous water (H 2O). If 2.16 g of water is produced from the reaction of 2.91 g of butane and 14.7 g of oxygen gas, calculate the percent yield of water. Be sure your answer has the correct number of significant digits in it. Determine Equation 2CH 3(CH 2) 2CH 3(g) + 13O 2(g) 8CO 2(g) +10H 2O(g) Caluclate n O g O 2 ( 1 O 2 ) = g O 2 Caluclate n CH3 (CH 2 ) 2 CH g CH 3 (CH 2 ) 2 CH 3 ( 1 CH 3 (CH 2 ) 2CH 3 ) = g CH 3 (CH 2 ) 2 CH 3 Determine the n CH3 (CH 2 ) 2 CH 3 needed to fully react of O O 2 ( 2 CH 3 (CH 2 ) 2CH 3 ) = CH 13 O 3 (CH 2 ) 2 CH 3 2 Since we only have of CH 3(CH 2) 2CH 3, CH 3(CH 2) 2CH 3 is the limiting reagent Calucalte n H2 O CH 3(CH 2) 2CH 3 (LR) O 2 CO 2 H 2O Initial () Change -2x = x = x = x =0.251 Final x=0 x= Calculate m H2 O H 2 O ( g H 2O 1 H 2 O 2O Determine percent Yield 2.16g 100% = 47.8% 4.52 g 4

5 2) 18 pts Terephthalic acid is an important chemical used in the manufacture of polyesters and plasticizers. It contains only C, H, and O. Combustion of mg terephthalic acid produces mg CO 2 and 6.45 mg H 2O. If of terephthalic acid has a mass of 41.5 g, determine the ecular formula of terphthalic acid. C xh yo z + O 2 CO 2 + H 2O (Combustion Reaction) All of the carbon in the compound goes into forming CO 2. Therefore, the es of CO 2 will equal the es of C in the compound. Determine n C mg CO 2 ( 1 g 1000 mg ) ( 1 CO 2 1 C ) ( ) = C g CO 2 1 CO 2 All of the hydrogen in the compound goes into forming H 2O. Therefore, the es of H 2O will equal two times the e of H in the compound mg H 2 O ( 1 g ) ( 1 H 2O 2 H ) ( ) = mg g H 2 O 1 H 2 O 10 4 H To find the mass of O, find the mass of C and H and subtract them from the overall weight of the compound. Calculate m C m C = g C C ( ) = g C 1 C Calculate m H m H = g H H ( ) = H 10 4 g H Calculate m O m O = m Cx H y O z m C m H m Cx H y O z = mg ( 1 g 1000 mg ) = g m O = g g g = g Calculate n O 1 O g ( ) = g O 10 4 O Divide through by smallest e amount ( ) Carbon Hydrogen Oxygen = = = Multiple through by 2 to get whole numbers Empirical Formula C 4H 3O 2 M C4 H 3 O 2 = g Find ecular formula M = m n = g 166 g g = 166 g = 2.00 Multiply empirical formula by 2: C 8H 6O 4 5

6 Multiple Choice Questions On the ParScore form you need to fill in your answers, perm number, test version, and name. Failure to do any of these things will result in the loss of 1 point. Your perm number is placed and bubbled in under the ID number. Do not skip boxes or put in a hyphen; unused boxes should be left blank. Bubble in your test version (B) under the test form. Note: Your ParScore form will not be returned to you, therefore, for your records, you may want to mark your answers on this sheet. Each multiple choice question is worth 5 points. 1. An element's most stable ion forms an ionic compound with chlorine having the formula XCl 2. If the mass number of the ion is 24 and it has 10 electrons, what is the element and how many neutrons does it have? a. Ne, 16 neutrons b. O, 16 neutrons c. Mg, 12 neutrons d. Ne, 14 neutrons e. None of the above 2. A reaction of 3L of X 4 gas and 4L of Y gas yields 4L of product. There is no excess X 4 or Y gas after the reaction goes to completion. All of the gas volumes are at the same temperature and pressure. What is the formula of the gaseous product? a. X 2Y 2 b. X 3Y c. X 4Y d. X 5Y e. None of the above 3. The average mass of a boron atom is If you were able to isolate a single boron atom, what is the chance that you would randomly get an atom with mass 10.81? a % b. about 11% c. 0% d. greater than 50% e. 0.81% 4. According to the law of definite proportions, a. the total mass after a chemical change is the same as before the change. b. the ratio of the masses of the elements in a compound is always the same. c. if the same two elements form two different compounds, they do so in the same ratio. d. it is not possible for the same two elements to form more than one compound. e. none of the above accurately explain the law of definite proportions. 6

7 5. Which of the following represents a pair of isotopes? a. O 2, O 3 b S, 32 16S 2 c. 15 7N, 15 8O d. 18 8O, 19 9F e. None of the above 6. Which one of the following statements about atomic structure is false? a. The number of protons and the number of neutrons are always the same in the neutral atom. b. Almost all of the mass of the atom is concentrated in the nucleus. c. The electrons occupy a very large volume compared to the nucleus. d. The protons and neutrons in the nucleus are very tightly packed. e. All of the above statements are true. 7

Chem. 1A Midterm 1 Version A October 14, 2016

Chem. 1A Midterm 1 Version A October 14, 2016 First initial of last name Name: Print Neatly. You will lose 1 point if I cannot read your name or perm number. Perm Number: All work must be shown on the