Chem 127, Final Exam December 10, 2003

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1 I. (55 points) This part of the final corresponds to Exam I. It covers the material in Chapters 1, 2 and 3. A. (10 points) Answer the following questions by writing your answers on the blanks provided. Only these answers will be graded. 1. Potassium sulfate has a solubility of 15 g/100 g of water at 40 C. A homogeneous solution is prepared by adding 39.0 g of potassium sulfate to 200 g of water at 40 C. Is the solution unsaturated, saturated or supersaturated? 2. How many protons are there in Zr4+? 3. How many electrons are there in Zr4+? 4. How many neutrons are there in Zr4+? 5. Classify potassium as a metal or a nonmetal. 6. Classify selenium as a metal or a nonmetal. 7. Write the formula for hydrogen peroxide 8. Write the name of the following compound:hno 3 (aq) 9. Write the formula for iron(iii) carbonate 10. Write the name of the following molecule: NF 3 B. (12 points) Answer the questions below, using LT (for is less than ), GT (for is greater than ), EQ (for is equal to ), or MI (for more information required ) in the blanks provided. 1. The number of gold atoms in g of gold is (1) x An element has two isotopes A and B. If the abundance of isotope A is 50%, the abundance of isotope B must be (2) that of isotope A. 3. In the reaction of combustion of glucose, glucose (C 6 H 12 O 6 ) reacts with oxygen to produce only carbon dioxide and water. In the balanced equation for this reaction (using the smallest whole numbers as stoichiometric coefficients), the sum of the stoichiometric coefficients on the product side is (3) g of nitrogen gas (4) 2 moles of nitrogen atoms. 1

2 C. (9 points) Turquoise has the following chemical formula: CuAl 6 (PO 4 ) 4 (OH) 8 4H 2 O The molar mass of turquoise is: g / mol. 1. What is the mass percent of oxygen in turquoise? 2. How many molecules of turquoise are in 2.25 grams? 3. How many atoms of phosphorus are in 2.25 grams of turquoise? D. (12 points) The reaction involved in the combustion of acetylene is: 2C 2 H 2 (g) + 5 O 2 (g) 4CO 2 (g) + 2 H 2 O (g) 1. How many moles of CO 2 (g) can be obtained from 6.50 mol of acetylene (assuming 100% yield and an excess of oxygen) 2. How many moles of CO 2 (g) can be obtained from 5.50 mol of oxygen (assuming 100% yield and an excess of acetylene) THIS PROBLEM IS CONTINUED ON THE FOLLOWING PAGE. 2

3 THIS PROBLEM CONTINUES FROM PAGE If 6.50 moles of acetylene are made to react with 5.50 moles of oxygen, what is the theoretical yield (in grams) of CO 2 (g) (MM = g/mol)? 4. If 68.5 L of CO 2 (g) (d = 1.85 g / L) is produced, what is the percent yield of the reaction? E. (9 points) Ibuprofen is made of carbon, hydrogen and oxygen. A sample of ibuprofen weighing g is burned in oxygen. At the end of the experiment, it is determined that g of water and g of carbon are obtained. 1. How many grams of hydrogen are present in the sample? 2. How many grams of oxygen are present in the sample? 3. How many moles of each element are there? = mol C = mol H = mol O F. (3 points) A compound made up of atoms A, B, and C is determined to contain 0.20 mol A, 0.40 mol B amd 0.50 mol C. What is the simplest formula of the compound? 3

4 II. (70 points) This part of the final corresponds to Exam II. It covers the material in Chapters 4 and 5. A. (10 points) ml of a M solution of Mg(OH) 2 is mixed with ml of a M solution of Ca(OH) How many moles of OH are present in the final mixture? 2. Assuming the final volume of the mixture to be ml, what is the molarity of Mg 2+ ions in the final mixture? B. (5 points) Hydrochloric acid (100.0 ml of M ) is added to ml of M Ba(OH) 2 solution. Assuming volumes to be additive, what is the molarity of OH in the final solution? C. (8 points) The density of a noble (group 18) gas is 1.63 g/l at 25 C and 1.00 atm? 1. What is the molar mass of the inert gas? 2. Write the symbol of the gas. 4

5 D. (15 points) A ml sample of M silver nitrate is mixed with M chromium (III) chloride. 1. How many moles of silver ion are initially present? 2. What is the minimum volume of chromium (III) chloride required to completely precipitate silver chloride? 3. How many grams of silver chloride precipitate (MM = g/mol) are produced? E. (15 points) Consider the reaction in basic medium between solid aluminum and permanganate ions. The unbalanced equation for this redox reaction is Al (s) + MnO 4 (aq) MnO 2 (s) + Al(OH) 4 (aq) You will need to balance the equation on scratch paper to answer the following questions. Write your answer on the blank provided. 1. What is the element oxidized? 2. What species is the reducing agent? 3. What is the element reduced? 4. How many electrons are lost in the balanced oxidation half reaction? 5. What is the coefficient of water in the final balanced equation? 5

6 F. (7 points) The following two questions are NOT related. 1. If a gas effuses 1.73 times faster than Kr, the molar mass of the gas must be (greater than, less than, equal to) the molar mass of Kr. 2. The lid is tightly sealed on an empty soda bottle at 27 C and 748 mm Hg. If the bottle is heated to 100 C, what is the pressure (in atm ) of the gas inside the bottle? G. (10 points) A sample of solid KClO 3 was heated in a test tube and decomposed according to the following reaction: 2KClO 3 (s) 2KCl (s)+3o 2 (g) The oxygen produced was collected by displacement of water at 22 C and at a total pressure of 754 mm Hg. The volume of the gas collected was L and the vapor pressure of water at 22 C is 21 mm Hg. (Assume 100% yield.) 1. What is the partial pressure of O 2 (in mm Hg) in the gas collected? 2. How many moles of KClO 3 are there in the sample that was decomposed? 6

7 III. (70 points) This part of the final corresponds to Exam III. It covers the material in Chapters 6, 7 and 8. A. (6 points) The following 2 problems are NOT related. There will be no partial credit given for these questions. 1. The Balmer series spectral lines of the hydrogen atom involve electron transitions from n= 2. What is the energy difference (in J/photon) for a transition from n = 5 to n = 2? 2. What is the frequency associated with light having a wavelength of 486 nm? B. (15 points) Write your answers on the blanks provided. 1. The symbol of the element represented by the electron configuration 1s 2 2s 2 2p 6 3s 2 3p The symbol of the element in Period 3 whose 2 anion is isolectronic with Ar. 3. The symbol of the element that is a +2 transition metal in Period 4 and has 3d 10 electrons 4. How many unpaired electrons are there in Mn 2+? 5. Write the abbreviated electron configuration for Cd. C. (6 points) Draw a circle around the correct answer. 1. Which is larger? Ar or Kr 2. Which is smaller? Se or Se 2 3. Which is more electronegative? Cl or Br 7

8 D. (6 points) Indicate whether each of the following statements about PBr 3 and its Lewis structure (given below) is true (Y) or false (N). Br P Br Br 1. The Br P Br angle is The hybridization for P is sp 3. E. (12 points) The Lewis structures for XeF 4 and SO 3 are provided below. Answer the questions about the properties of the molecule on the blanks provided. 1. XeF 4 2. SO 3 a. Electron pair geometry (Answers of the form AX m E n are unacceptable) b. Molecular geometry c. Is it polar? (Yes or No) F F Xe F F a. Electron pair geometry (Answers of the form AX m E n are unacceptable) b. Number of π bonds O S O O c. Are resonance structures possible? (Yes or No) F. (6 points) Write the Lewis structure for the isocyanate ion (CNO ) where N is the central atom. Write your final Lewis structure in the rectangle provided. 8

9 G. (5 points) In a coffee cup calorimeter, 50.0 ml of 1.00 M NaOH and ml of 1.00 MHCl are mixed. Both solutions are at 25 C. After the reaction, the temperature of the resulting mixture is 31.7 C. Assume that the solution has a density of 1.00 g/ml and a specific heat of 4.18 J/g C. Assume also that there is no heat loss to the calorimeter or surroundings. What is the enthalpy change for the solution described? H. (14 points) Consider the following thermochemical equation. Fe 2 O 3 (s) + 2 Al (s) Al 2 O 3 (s) + 2 Fe (s) H = kj 1. Is the reaction exothermic? 2. What is H f for Fe (s)? 3. What is H f for Fe 2 O 3 (s) if H f for Al 2 O 3 is kj? 4. What is H when 1.00 g of Al 2 O 3 (MM = 102 g/mol) is formed from the reaction above? (Do not use the answer you get from #3.) 9

10 IV. (55 points) This part of the final covers the material in Chapter 9. A. (10 points) Draw a circle around the correct answer. 1. Which has a higher boiling point? H 2 O(l) or H 2 Se 2. Which has larger dispersion forces? CCl 4 or CH 4 3. Which has dipole forces? SO 2 or CO 2 4. Which has hydrogen bonding? C 2 H 5 OH or H 3 CCOCH 3 5. Which is network covalent? diamond or aluminum B. (5 points) A given substance has H vap = 9.7 kj/mol. What is the ratio of vapor pressures if the temperature goes from 20 Cto40 C? C. (5 points) Consider liquid cyclohexane. At 25.5 C, its vapor pressure is mm Hg. If 6.00 x 10 4 mol of liquid cyclohexane are added to an evacuated 50.0 ml flask at 25.5 C, what is the pressure (in mm Hg) in the flask? 10

11 D. (15 points) Element X is a body centered crystal that has 2 atoms/unit cell. Element X has an atomic mass of 41.3 g/mole. 1. What is the mass of a unit cell of element X? 2. What is the volume of a unit cell of Atom X if its density is 3.14 g/cm 3? 3. Suppose a body centered crystal with the same unit cell dimensions is made up of elements X and Y where atom Y is in the center. The atomic mass of Element Y is 82.6 g/mol. Element X has an atomic mass of 41.3 g/mol What is the density of the crystal? 11

12 E. (10 points) Given the following data for a certain substance, X, fill in the blanks below. H sublimation = kj/mol H vaporization = kj/mol 1. H for the reaction: X(l) X (g) 2. H for the reaction: X(s) X (g) 3. H for the reaction: X(l) X (s) F. (10 points) Consider the phase diagram for a substance Y below. 1. Is the liquid phase the denser phase? 2. What is the normal boiling point of Y? 3. What is its physical state at 30 C, 15 mm Hg? 4. Can Y exist as a gas at 15 C and 25 mm Hg? 5. If Y is kept at 20mm Hg and the temperature is increased from 20 Cto20 C, what phase change occurs? 12

13 BONUS (15 points) All or nothing. The bonus should be done only after you have completed the main part of this exam and checked your work for errors. The time allotted for this exam does not include time for the bonus. (SHOW ALL WORK! Lucky guesses will not be considered.) A flask with a volume of L contains 1.00 g of hydrogen and 6.40 g of oxygen. The mixture is ignited and the following reaction takes place (100% yield). 2H 2 (g) + O 2 (g) 2H 2 O The mixture is cooled to 27 C. The vapor pressure of water at 27 C is 26.7 mm Hg. What is the pressure in the flask (in mm Hg) at27 C and after reaction is complete? 13

Chem 127, Final Exam December 14, 2001

Chem 127, Final Exam December 14, 2001 I. (55 points) This part of the final corresponds to Exam I. It covers the material in Chapters 1, 2 and 3. A. (8 points) Fill in the empty boxes with the appropriate symbol, number, word or charge. Nuclear