Hello, dear friend, you can consult us at any time if you have any questions, add WeChat: daixieit

Chemistry 11A

Practice Final Exam

Fall 2022

Part I  (40 points)

1.  (12 points—3 points each)

a)  A substance that can’t be broken down into simpler substances is considered

A) a homogeneous mixture

B) a heterogeneous mixture

C) an electron

D) an element

E) a compound

b)  Which of the following is an example of an intensive property?

A) density    

B) volume     

C) mass

D) None of these are intensive properties.

E) All of these are intensive properties.

c)  An ⁵⁶Fe²⁺ particle contains

A) 28 protons, 28 neutrons and 26 electrons.

B) 54 protons, 56 neutrons and 52 electrons.

C) 26 protons, 26 neutrons and 26 electrons.

D) 58 protons, 58 neutrons and 56 electrons.

E) 26 protons, 30 neutrons and 24 electrons.

d)  Which one of the following pairs of substances illustrates the Law of Multiple Proportions?

A) O₃, O₂

B) D₂O, H₂O

C) SiO₂, Sb₂O₃

D) KCl, MgCl₂

E) PCl₃, PCl₅

2.  (8 points)  Aerogels consist of a solid framework with most of their volume occupied by air.  Silica (SiO₂) powder has a density of 2.2 g/cm³.  Silica can be expanded into an aerogel with a density of 0.015 g/cm³.  Calculate the volume of silica aerogel that can be made from 125 cm³ of silica powder.

3.   (10 points) Common brass is a copper and zinc alloy containing 37.0% zinc by mass and having a density of 8.48 g/cm³.  A fitting composed of common brass has a total volume of 112.5 cm³.  How many atoms (copper and zinc) does the fitting contain?

4.  (10 points) Linear measurements made with the following ruler are recorded to the nearest ten thousandth of a millimeter. Mark the scale on the ruler in units of micrometers and record the measurement of the line to the correct number of significant figures.  Use the space below to show your thought process and all your work.

Part II  (40  points)

5.  (12 points—3 points each)

a)  A covalent bond is best described as:

A)  the transfer of electrons

B)  the sharing of electrons between atoms

C)  a bond between a metal and a non-metal

D)  a bond between a metal and a polyatomic ion

E)  a bond between two polyatomic ions

b)  An oxidizing agent

A) loses electrons.

B) must contain oxygen.

C) increases its oxidation number.

D) becomes oxidized.

E) none of these

c) What is the stoichiometric coefficient for oxygen when the following equation is balanced using the chemical formula for ethanol and the lowest, integer coefficients?

_____ ethanol (l) + _____ O₂ (g)  →  _____ CO₂ (g) + _____ H₂O (l)

A) 3 B) 5 C) 7 D) 9 E) none of these

d)  The equation representing the reaction between nitrogen and hydrogen to produce ammonia is shown below.  If 10.0 g of nitrogen is reacted with 5.0 g of hydrogen, which one of the following statements is false?  

N₂ (g) + 3 H₂ (g)  →  2 NH₃ (g)

A) The theoretical yield of ammonia is 15 g.

B) Hydrogen is the excess reactant.

C) Nitrogen is the limiting reactant.

D) 2.8 g of hydrogen are left over.

E)  All of these are true statements.

6. (12 points)

a) (6) Give the formula for the following compounds:

(i)  potassium phosphate _______________

(ii)  perchloric acid ________________

(iii)  carbon disulfide _______________

b)  (6) Name the following:

(i)  HNO₃ ___________________________

(ii)  CH₃NH₂ ___________________________

(iii)  CuI ____________________________

7.  (10 points)

a)   (4) Write net ionic equations to represent the reactions between each of the following two species.  If no reaction occurs, write the formulae for the dissociated ions ® NR

(i)  H₂SO₄ and KOH

(ii)  Al(C₂H₃O₂)₃ and LiNO₃

b)  (6) In the following redox reaction…

5 As₂O₃ (s) + 4 MnO₄^- (aq) + 9 H₂O (l) + 12 H⁺ (aq) ® 10 H₃AsO₄ (aq) + 4 Mn²⁺ (aq)

(i)  …the element _________ is oxidized from ________ to _______.

(ii)  …the element __________ is reduced from _______ to ______ .

(iii)  …the total number of moles of electrons transferred is ____________.

8.  (6 points) Rust stains can be removed by washing a surface with a dilute solution of oxalic acid (H₂C₂O₄):

___Fe₂O₃ (s) + ___H₂C₂O₄ (aq) ® ___[Fe(C₂O₄)₃]^3- (aq) + ___H⁺ (aq) + ___H₂O (l) 

a)  Balance the equation above and determine the mass of rust that can be removed by 0.500 L of a 0.14 M solution of oxalic acid. 

b)  Is this an oxidation-reduction reaction (circle one)?

Part III (40 points)

9.  (12 points—3 points each)

a)  Given the following equation,

2 H₂ (g) + O₂ (g)  ® 2 H₂O (l)   DH° = −571.6 kJ/mol,

which statement is incorrect?

A) DH° for the reverse reaction is +571.6 kJ mol^-1.

B) DH° for forming one mole of liquid water is −285.8 kJ mol^-1.

C) DH° for the reaction of half a mole of oxygen is −285.8 kJ mol^-1.

D) The standard heat of formation of liquid water is −571.6 kJ mol^-1.

E) The equation forming gaseous water would have a different DH°.

b)  A piece of iron (C_s = 0.449 J g^-1 °C^-1) and a piece of gold (C_s = 0.128 J g^-1 °C^-1) have identical masses.  If the iron has an initial temperature of 498 K and the gold has an initial temperature of 298 K, which of the following statements is true of the outcome when the two metals are placed in contact with one another?  Assume no heat is lost to the surroundings.

A) Since the two metals have the same mass, but the specific heat capacity of iron is much greater than that of gold, the final temperature of the two metals will be closer to 498 K than to 298 K.

B) Since the two metals have the same mass, the final temperature of the two metals will be 398 K, exactly halfway between the two initial temperatures.

C) Since the two metals have the same mass, but the specific heat capacity of gold is much smaller than that of iron, the final temperature of the two metals will be closer to 298 K than to 498 K.

D) Since the two metals have the same mass, the thermal energy contained in the iron and gold after reaching thermal equilibrium will be the same.

E) None of the above is true.

c)  The assumptions of the kinetic-molecular theory are most likely to be correct under what conditions?

A) high temperature-low pressure

B) high temperature-high pressure

C) low temperature-high pressure

D) low temperature-low pressure

E) They are always correct.

d)  Which of the following laws concerning gases is misstated?

A) In a mixture of gases, the total pressure of the gases equals the sum of the individual pressures of each gas.

B) At fixed temperature and pressure, the volume of a gas is inversely proportional to the number of moles of that gas.

C) At fixed pressure, the volume of a gas is directly proportional to its temperature in Kelvin.

D) At fixed temperature, the volume of a gas is inversely proportional to its pressure.

E) The average translational kinetic energy of the molecules of a gas is directly proportional to the temperature in Kelvin.

10.  (10 points)

a)  (5)  A mixture of 2.0 L of hydrogen and 2.0 L of oxygen at the same temperature and pressure react to form the theoretical yield of water vapor (at the same temperature and pressure). What is the expected final volume of water vapor, in L?

b)  (5) It took 49 sec for 1.0 L of helium to effuse through a pinhole. How long will it take for 1.0 L of methane to effuse under identical conditions?

11.  (10 points) At 25 °C and constant pressure, carbon monoxide gas combines with oxygen gas to give carbon dioxide gas with the evolution of 10.1 kJ per gram of carbon monoxide consumed. What is the value of DH for the production of one mole of carbon dioxide gas?

12.  (8 points) Use the data below to calculate the standard enthalpy of formation of ethane gas.  ALL work must be shown for credit!  [Hint:  Write your “target reaction” first!]

Reaction	DH°rxn (kJ mol-1)
2 C2H6 (g) + 7 O2 (g) ® 4 CO2 (g) + 6 H2O (l)	−3119.6
C (s, graphite) + O2 (g) ® CO2 (g)	−393.5
H2 (g) + ½ O2 (g) ® H2O (l)	−285.8

Part IV (40 points)

13.  (12 points—3 points each)

a)  Which of the following visible colors of light transmits (or reflects) the longest wavelength?

A) blue     B) green     C) yellow     D) orange     E) violet

b) Choose the ground state electron configuration for Cr³⁺.

A) [Ar]4s¹3d²     B) [Ar] C) [Ar]4s²3d⁶ D) [Ar]3d³ E) [Ar]4s²3d¹

c)  For which of the following types of electromagnetic radiation would the photons have the highest frequency?

A) X-rays B) ultraviolet C) visible D) infrared E) microwaves

d) How many of the following species are diamagnetic?

Cs    Zr²⁺     Al³⁺    Hg²⁺

A) 0    B) 1      C) 2     D) 3     E) 4    

14.  (8 points) Some alarm systems use the photoelectric effect.  A beam of light strikes a piece of metal, ejecting electrons continuously and causing an electric current to flow.  When someone steps into the light beam, the current is interrupted and the alarm is triggered.  What is the maximum wavelength of light that can be used in such an alarm system if the photocell metal is sodium with a binding energy of 266 kJ mol^-1?

15. (12 points) Give the set of four quantum numbers that represent…

a)  …the last electron added (using the Aufbau principle) to the Zn atom.

b)  …the electron gained to form the bromine ion from the bromine atom.

c)  …the electron lost to form the Rb ion from the Rb atom.

16.  (8 points)  

a)  Write the reaction that represents the removal of the first core electron from P.

b)  Place the following in order of increasing radius:

Se As S Se^2-

      ______     <     _______    <   _______   <  _______

Part V (40 points)

17.  (12 points—3 points each)

a)  Which of the following elements can form compounds with an expanded octet?

A) N                B) Br                C) F        D) Be

E) None of these elements can form compounds with an expanded octet.

b)  Place the following in order of increasing dipole moment.

I.  BF₃ II.  BIF₂   III.  BClF₂

A) I  <  II  =  III B) II  <  III  <  I C) I  <  II  <  III D) II  <  I  <  III

E) I  <  III  <  II

c)  Give the molecular geometry and number of electron groups for BrF₃.

A) trigonal pyramidal, 4 electron groups

B) trigonal planar, 3 electron groups

C) T-shaped, 5 electron groups

D) trigonal planar, 5 electron groups

E) seesaw, 5 electron groups

d)  According to molecular orbital theory, how many of the following species are paramagnetic?

B₂ C₂ N₂^2- F₂²⁺

A) 4 B) 3 C) 2 D) 1 E) 0

18. (7 points) Draw three resonance structures for SO₂.  Determine which structure is likely to be the most important contributor to the resonance hybrid of sulfur dioxide and briefly explain your choice.

19.  (13 points)  Vitamin B₆ (pyridoxine) is an organic compound.  In humans, vitamin B₆ deficiency can cause apathy, irritability, and an increased susceptibility to infections.  Below is an incomplete Lewis structure for vitamin B₆.  Complete the Lewis structure, giving all atoms zero formal charge and answer the following questions:

a.  How many σ bonds exist in vitamin B₆? __________

b.  How many π bonds exist in vitamin B₆? __________

c.  Give the approximate angles for the bonds in the structure marked a – g:

d.  How many carbon atoms are sp² hybridized? _________

e.  How many of the following atoms are sp³ hybridized?

nitrogen_______ oxygen _______ carbon _______

20.  (8 points)  The ionization energy for a gaseous fluorine atom is 1681 kJ mol^-1, while a diatomic fluorine molecule has a lower ionization energy of 1515 kJ mol^-1.  Label the orbitals in the energy level diagram below and use molecular orbital theory to explain the difference in ionization energies between F and F₂.