Quiz 8

Quiz 8 Due: 11:59pm on Monday, December 10, 2012 Note: You will receive no credit for late submissions. To learn more, read your instructor's Grading Policy

Question 1 Part A Write Lewis structure for

(both

atoms are bonded to

).

Draw the molecule by placing atoms on the grid and connecting them with bonds. Include all lone pairs of electrons. Include all hydrogen atoms. ANSWER:

Correct

Part B Write the Lewis structure for

(One H per O).


Correct

Part C Write Lewis structure for

(contains a

bond).

Draw the molecule by placing atoms on the grid and connecting them with bonds. Include all lone pairs of electrons. ANSWER:

Correct

Part D Write Lewis structure for

.

IMPORTANT: Include all lone pairs of electrons and show any non-zero formal charges in the correct structure. ANSWER:

Correct

Part E Write Lewis structure for

(

is bonded to

).

IMPORTANT: Minimize your formal charges on this one!! ANSWER:

Correct

Part F Write Lewis structure for

.


Correct

Question 2 Bromine pentaiodide,

, is used for research purposes in scientific laboratories. Clearly one would like to know quite a bit about the chemical nature

of this compound. Therefore, to answer the questions in this problem, you will need to draw the Lewis structure of bromine pentaiodide.

Part A What is the electron-domain (charge-cloud) geometry of

?

Enter the electron-domain geometry of the molecule.

Hint 1. Determine the steric number The number of electron domains (also called charge clouds) around the central atom of a molecule is often called the steric number. What is the steric number of this molecule? Express your answer as an integer.

Hint 1. How to approach the problem The steric number is equal to the number of outer atoms plus the number of lone pairs on the central atom.

Hint 2. Determine the number of outer atoms How many outer atoms are bonded to the central atom in this molecule? Express your answer as an integer. ANSWER: 5

Hint 3. Determine the number of lone pairs How many lone pairs are on the central atom of this molecule? Express your answer as an integer. ANSWER:

1

ANSWER: 6

ANSWER: octahedral

Correct

Part B What is the molecular geometry of

?

Enter the molecular geometry of the molecule.

Hint 1. How to approach the problem The molecular geometry can be determined from the electronic geometry and the number of lone pairs on the central atom.

Hint 2. Determine the number of lone pairs How many lone pairs are on the central atom of this molecule? Express your answer as an integer. ANSWER: 1

ANSWER: square pyramid

Correct

Part C Ignoring lone-pair effects, what is the smallest bond angle in

?

Express your answer as an integer.

Hint 1. How to approach the problem Knowing the electronic geometry of the molecule will allow you to determine the bond angles. Recall that the repulsion between the electron regions causes them to exist as far apart from each other as possible.

ANSWER: 90

degrees

Correct

Part D Which choice best describes the polarity of

?

Hint 1. Determine the electronegativity Is there a difference in electronegativity between

and

?

ANSWER: Yes No

Hint 2. Determine the arrangement of the bonds Based on the molecular geometry of this molecule, are the bonds arranged symmetrically about the central atom (such that bond polarities would cancel)? ANSWER: Yes No

ANSWER: The molecule is polar and has polar bonds. The molecule is nonpolar and has polar bonds. The molecule is polar and has nonpolar bonds. The molecule is nonpolar and has nonpolar bonds.

Correct

Question 3 Part A Draw Lewis structures for ethane

, ethylene

, and acetylene

.

Draw the molecules by placing atoms on the grid and connecting them with bonds. Include all hydrogen atoms. ANSWER:

Correct

Part B What is the hybridization of the carbon atoms in ethane? ANSWER:

Correct

Part C What is the hybridization of the carbon atoms in ethylene? ANSWER:

Correct

Part D What is the hybridization of the carbon atoms in acetylene? ANSWER:

Correct

Part E How many

bonds are there in each molecule?

Expess your answers as integers. Enter your answers in the given order separated by commas. ANSWER: ethane, ethylene, acetylene 7,5,3

bonds

Correct

Part F How many

bonds are there in each molecule?

Expess your answers as integers. Enter your answers in the given order separated by commas. ANSWER: ethane, ethylene, acetylene 0,1,2

bonds

Correct

Question 4 Part A Indicate the hybridization of the central atom in ANSWER:

.

Correct

Part B Indicate the hybridization of the central atom in

.

ANSWER:

Correct

Part C Indicate the hybridization of the central atom in

.

ANSWER:

Correct

Part D Indicate the hybridization of the central atom in

.

ANSWER:

Correct

Question 5 Molecular orbital (MO) theory is based in quantum mechanics and treats the orbitals found in a molecule in a manner similar to atomic orbitals in an atom. It successfully accounts for or predicts certain chemical and physical properties more accurately than other bonding theories. The stability, bond length, bond order, and magnetism of a molecule can be predicted from its molecular orbital configuration. The electrons available in a molecular species are placed in molecular orbitals following the same rules used in electron configurations: the aufbau principle, Hund's rule, and the Pauli exclusion principle.

Part A

Arrange the following in order of decreasing stability. A blank molecular orbital diagram has been provided to help you. Rank the fluorine species from most to least stable. To rank items as equivalent, overlap them.

Hint 1. Factors determining stability Stability increases with bond order. This is because higher bond orders represent MO configurations with more bonding electrons and fewer antibonding electrons. Bonding electrons are lower in energy and tend to stabilize the species. After drawing a MO diagram, you can count the number of bonding and antibonding electrons and then use the following formula:

Hint 2. Determine the bond order of Based on the MO configuration, what is the bond order of

?

Express your answer numerically.

Hint 1. How to approach the problem First, fill the following diagram with valence electrons. As with atomic orbital diagrams, fill from low to high energy and put no more than two electrons in any given orbital.

Then, apply the following formula:

Hint 2. Determine the total number of valence electrons How many valence electrons are present in

?

Express your answer numerically as an integer.

Hint 1. How to determine the number of electrons

For a neutral species, add the number of valence electrons for each atom present. Anions have more electrons than neutral species whereas cations have fewer electrons. For example, has 12 valence electrons, has 14 valence electrons, and

has 10 valence electrons.

ANSWER: 13

Hint 3. Count the numbers of bonding and antibonding electrons Of the 13 valence electrons in

, how many are in bonding orbitals and how many are in antibonding orbitals?

ANSWER: 7 in bonding and 6 in antibonding orbitals 8 in bonding and 5 in antibonding orbitals 5 in bonding and 8 in antibonding orbitals 6 in bonding and 7 in antibonding orbitals

ANSWER: 1.5


?

Express the bond order numerically.




?


ANSWER: 14

Hint 3. Count the numbers of bonding and antibonding electrons Of the 14 valence electrons in



ANSWER: 1.0


?

Express the bond order numerically.




?

Express your answer numerically as an integer. ANSWER: 15

Hint 3. Count the numbers of bonding and antibonding electrons

Of the 15 valence electrons in



ANSWER: 0.5

ANSWER:

Correct

Part B Which of the following diatomic species are paramagnetic and which are diamagnetic? A blank molecular orbital diagram has been provided to help you. Drag the appropriate items to their respective bins.

Hint 1. How to approach the problem Diamagnetic substances are weakly repelled by a magnetic field because all electrons are paired. Paramagnetic substances are attracted to a magnetic field because they contain unpaired electrons. To determine whether a species contains unpaired electrons, construct a molecular orbital diagram.

Pay close attention to Hund's rule, which states that, within a set of degenerate orbitals, each gets one electron before any are paired.

Hint 2. Determine the number of unpaired electrons in the MO diagram for How many unpaired electrons would be present in a MO diagram for Express your answer numerically as an integer.

Hint 1. Determine the number of valence electrons in How many valence electrons are in

?


ANSWER: 2

?

Hint 3. Determine the number of unpaired electrons in the MO diagram for How many unpaired electrons would be present in a MO diagram for

?



?


ANSWER: 1

Hint 4. Determine the number of unpaired electrons in the MO diagram for How many unpaired electrons would be present in a MO diagram for Express your answer numerically as an integer.


?


ANSWER: 0

ANSWER:

?

Correct

Question 6 If we assume that the energy-level diagrams for homonuclear diatomic molecules shown in Figure 9.43 in the textbook can be applied to heteronuclear diatomic molecules and ions, predict the bond order and magnetic behavior of each of the following. Use the MO diagram from Figure 9.43 for large 2s2p interactions for parts a - d. Use the MO diagram from Figure 9.43 for small 2s-2p interactions for parts e - h.

Part A

Enter your answer numerically. ANSWER: = 2.5

Correct

Part B

ANSWER:

magnetic behavior

diamagnetic paramagnetic

Correct

Part C


Correct

Part D

ANSWER:

magnetic behavior


Correct

Part E


Correct

Part F

ANSWER:

magnetic behavior

Correct


Part G


Correct

Part H

ANSWER:

magnetic behavior


Correct

Question 7 Identify the carbon atom(s) in the structure shown that has (have) each of the following hybridizations.

Part A . Highlight the appropriate atoms by clicking on them. ANSWER:

Correct

Part B . Highlight the appropriate atoms by clicking on them. ANSWER:

Correct

Part C . Highlight the appropriate atoms by clicking on them. ANSWER:

Correct

Question 8 Alkanes are molecules that contain only carbon and hydrogen and have only single bonds. Straight-chain alkanes have all the carbon atoms connected in a row, branched-chain alkanes have branching connections of carbon atoms, and cycloalkanes contain rings of carbon atoms.

Molecular model of an alkane Consider the alkane shown in the model.

Part A What is the molecular formula for the alkane shown in the model? Express your answer as a chemical formula.

Hint 1. How to approach the problem Count the total number of carbon atoms in the molecule. Then count the number of hydrogen atoms. Finally, write the molecular formula. The carbon atoms are color-coded: Black spheres represent carbon atoms and gray spheres represent hydrogen atoms. However, even if you didn't know this color scheme, you could figure it out based on the number of bonds formed by each atom.

Hint 2. Determine the number of carbon atoms How many carbon atoms are present? Express your answer numerically as an integer. ANSWER:

7

Correct

Hint 3. Determine the number of hydrogen atoms How many hydrogen atoms are present? Express your answer numerically as an integer. ANSWER: 16

Correct

Hint 4. How to write a molecular formula Write the symbol for carbon, followed by the number of carbon atoms in the molecule. Then write the symbol for hydrogen followed by the number of hydrogen atoms.

ANSWER:

Correct It is much more convenient to write

than it is to draw the molecule. However, this molecular formula does not describe the structure of

the molecule. A condensed structure is a way to express how the atoms are arranged without drawing the full structure. For this example, the condensed structure is .

Part B Name the alkane shown in the model. Express your answer as the IUPAC name.

Hint 1. How to approach the problem Name the main chain according to the number of carbon atoms. Then number the main carbon chain. Identify the substituents and name them according to their location in the main carbon chain. The full name of the alkane will contain a prefix denoting the type and placement of substituents, a parent name indicating the number of carbon atoms, and the suffix ane.

Hint 2. Name the main carbon chain Name the main chain of the alkane shown. Express your answer using IUPAC naming. Enter only the name of the main chain.

Hint 1. Determine the number of carbon atoms in the main chain How many carbon atoms are in the main chain? Express your answer numerically as an integer.

ANSWER: 5

ANSWER: pentane

Correct

Hint 3. Name the substituents What name denotes the substituent

?

Spell out the full name of the substituent. ANSWER: methyl

Correct

Hint 4. Number the substituents Assign a number to each substituent group based on the carbon to which it is attached. Enter the numbers of the carbon atoms that have substituent groups separated by commas. Enter the lower number first (e.g., 1,4). ANSWER: 2,3

Correct Numbering the chain from right to left puts the branches at positions 2 and 3 . Numbering from left to right puts them at positions 3 and 4. In this case, numbering from right to left produces the lowest position numbers and is therefore the preferred direction.

ANSWER: 2,3-dimethylpentane

All attempts used; correct answer displayed

Part C Draw the structure of the cycloalkane 1,4-dimethylcyclohexane. Draw the molecule by placing atoms on the grid and connecting them with bonds. Include all hydrogen atoms.

Hint 1. How to approach the problem

First draw the cycloalkane ring. Then add the substituents to the ring at the positions given in the question.

Hint 2. Draw the ring The base of this structure is a cyclohexane ring. Draw cyclohexane including all hydrogen atoms. Draw the molecule by placing atoms on the grid and connecting them with bonds. Include all hydrogen atoms. ANSWER:

Answer Requested The name cyclohexane describes a cycloalkane with six carbon atoms in the ring.

Hint 3. Determine which carbon atoms have substituents attached Select the carbon atoms that have attached substituent groups. Highlight the appropriate atoms by clicking on them. ANSWER:

Correct

Hint 4. Adding substituents After determining the structure of the ring, you need to add the methyl substituents. Add a methyl substituent ( atoms specified in the name 1,4-dimethylcyclohexane.

ANSWER:

Correct

Question 9 Give the name or condensed structural formula, as appropriate.

Part A

ANSWER: 3,5-dimethylheptane 2,3-dimethylheptane 3,3-dimethylheptane 2,3-diethylheptane

Correct

Part B 2,2-dimethylpentane Draw the molecule by placing atoms on the grid and connecting them with bonds.

) to each of the carbon

ANSWER:

Correct

Part C 4-ethyl-1,1-dimethylcyclohexane Draw the molecule by placing atoms on the grid and connecting them with bonds. ANSWER:

Answer Requested

Part D

ANSWER:

2,5,5-trimethylhexane 2,2,5-trimethylhexane 2,2,5-triethylhexane 2,5,5-triethylhexane

Correct

Part E

ANSWER: 3-ethylheptane 4-ethylheptane 1-ethylheptane 2-ethylheptane

Correct

Question 10 Part A Name the following compound.

Spell out the full name of the compound. ANSWER: 1-pentene

Correct

Part B Name the following compound.

Spell out the full name of the compound. ANSWER: 2-pentene

Correct

Part C Name the following compound.

Spell out the full name of the compound. ANSWER: 2-methyl-1-butene

All attempts used; correct answer displayed

Part D Name the following compound.


Correct

Part E Name the following compound.


Correct

Question 11 Learning Goal: To recognize and identify specific functional groups within organic molecules. Functional groups are groups of atoms that replace

atoms on hydrocarbons. Functional groups allow complex organic molecules to be built from

simple hydrocarbon starting molecules. Some of the more important functional groups are listed in the table here. Class Alcohols Amines

Functional group

Formula

Aldehydes Ketones Carboxylic acids

Part A Classify the organic compounds by the class of their functional group. Drag the appropriate items to their respective bins.

Hint 1. How to approach the problem Identify the functional group in the organic compound and then find the corresponding class from the table provided in the introduction.

Hint 2. How to distinguish among oxygen-containing functional groups Keep in mind that ketone functional groups must be bound to internal carbon atoms, not to a carbon atom at the end of a chain. Also, alcohol groups are usually written with the oxygen next to the carbon to which it binds ( or ), whereas aldehyde groups are written with the hydrogen atom next to the carbon (

Hint 3. Identify the functional group in The functional group in ANSWER:

ANSWER:

is

).

Correct

Question 12 Identify each of the functional groups in the following molecules:

Part A Check all that apply.

ANSWER:

cis-alkene aromatic ring alcohol amine amide alkene trans-alkene ether ketone aldehyde

Correct

Part B Check all that apply.

ANSWER: alcohol aromatic ring cis-alkene amine ketone ether alkene aldehyde trans-alkene amide

Correct

Part C

Check all that apply.

ANSWER: ketone alkene aromatic ring amine cis-alkene alcohol trans-alkene aldehyde ether amide

Correct

Part D Check all that apply.

ANSWER:

aromatic ring aldehyde alkene amine ketone cis-alkene trans-alkene alcohol amide ether

Correct

Question 13 Learning Goal: To calculate the concentration of a solution using acid–base titration data. In an acid–base titration, an acid (or base) of known concentration is added to a base (or acid) of unknown concentration until the number of moles of and are equal, a condition called the equivalence point. Since you know the number of moles of (or ) that you added, you can determine the number of moles of

(or

For example, a solution containing 1

) in the unknown solution.

of

contains 2

of ionizable hydrogen atoms, and would therefore require 2

of

for

neutralization. A chemist needs to determine the concentration of a solution of nitric acid, indicator. She then slowly adds 0.400 that 115

of

. She puts 865

of the acid in a flask along with a few drops of

to the flask until the solution turns pink, indicating the equivalence point of the titration. She notes

was needed to reach the equivalence point.

Solution map In this titration, the concentration of base is known and can be used to calculate the unknown acid concentration:

Part A How many moles of

are present in 115

Express your answer numerically in moles.

Hint 1. Identify the appropriate formula If the formula for molarity is

what is the formula for moles? ANSWER:

of 0.400

?

Hint 2. Convert the volume to liters Convert 115

to liters.

Express your answer numerically in liters. ANSWER: 0.115

ANSWER: 4.60!10"2

Correct

Part B How many moles of

are present if 4.60!10"2

of

was needed to neutralize the acid solution?

Express your answer numerically in moles.

Hint 1. How to approach the problem At the equivalence point,

. Look at the formula for the acid, and note the number of

look at the formula for the base, and note the number of

ions per formula unit. Would you need more moles of acid, more moles of

base, or equal moles of each to reach the equivalence point?

Hint 2. Determine the relative amounts of acid and base at the equivalence point ______ ANSWER: 1, 1 1, 2 2, 1 2, 3 3, 2

ANSWER: 9.20!10"2

of

will neutralize ______

of

ions per formula unit. Similarly,

.

Correct

Part C What is the concentration of

if 9.20!10"2

are present in 865

of the solution?

Express the molar concentration numerically.

Hint 1. Identify the proper mathematical operation The unit of molarity, If

, is equivalent to the unit of moles per liter,

is the number of moles of solute and

. For example,

.

is the volume in liters, what operation will give units of moles per liter?

ANSWER:

Hint 2. Convert the volume to liters Convert 865

to liters.

Express your answer numerically in liters. ANSWER: 0.865

ANSWER: 0.106

Correct

Question 14 Learning Goal: To recognize what intermolecular forces are present in a given compound and which of those forces is predominant. Chemists use the term intermolecular forces to describe the attractions between two or more molecules. Dipole-dipole forces result from the attraction of the positive end of one polar molecule to the negative end of another polar molecule. Hydrogen bonding is a particularly strong type of dipole-dipole force that occurs when hydrogen is attached to nitrogen, oxygen, or fluorine. Water is an example of a substance in which hydrogen bonding occurs. Because of oxygen's high electronegativity and the electron deficiency of the hydrogen atom, the hydrogen atoms are attracted to the lone pairs of electrons on the oxygen of another water molecule. All substances have dispersion forces, also known as London forces. These forces are very weak and are only important in the absence of any other intermolecular force. Nonpolar covalent molecules and single-atom molecules are examples of substances that lack all other intermolecular forces except for dispersion. Dispersion forces result from shifting electron clouds, which can cause a weak, temporary dipole.

Part A What is the predominant intermolecular force in each of these compounds: water (

), carbon tetrachloride (

)? Drag the appropriate items to their respective bins.

Hint 1. Identify intermolecular forces present in water Which intermolecular forces are present in water,

?

Check all that apply. ANSWER: dipole-dipole forces hydrogen bonding dispersion forces

Hint 2. Identify intermolecular forces present in carbon tetrachloride Which intermolecular forces are present in carbon tetrachloride,

?


Hint 3. Identify intermolecular forces present in hydrogen sulfide Which intermolecular forces are present in hydrogen sulfide,

?


Hint 4. Determine the relative strength of intermolecular forces In general, arrange the intermolecular forces in decreasing order of strength. Rank the intermolecular forces from strongest to weakest. To rank items as equivalent, overlap them. ANSWER:

), and hydrogen sulfide (

ANSWER:

Correct

Question 15 Learning Goal: To learn how to calculate the solubility from

and vice versa.

Consider the following equilibrium between a solid salt and its dissolved form (ions) in a saturated solution: At equilibrium, the ion concentrations remain constant because the rate of dissolution of solid

equals the rate of the ion crystallization. The

equilibrium constant for the dissolution reaction is

is called the solubility product and can be determined experimentally by measuring the solubility, which is the amount of compound that dissolves per unit volume of saturated solution.

Part A A saturated solution of lead(II) chloride, was found to be 1.62!10"2

. Calculate

, was prepared by dissolving solid for

in water. The concentration of

ion in the solution

.

Express your answer numerically.

Hint 1. Find the concentration of

using stoichiometry

dissolves to produce 1.62!10"2

If solid

, what concentration of

ion is produced?

Express the molar concentration numerically.

Hint 1. How to approach the problem Under the assumption of complete dissociation, each mole of

Consider how the concentration of

will compare to the concentration of

ANSWER: = 3.24!10"2

Hint 2. Identify the

expression

The balanced equation for the complete dissociation of

What is the expression for the solubility product? ANSWER:

produces one mole of

is

.

and two moles of

:

ANSWER: = 1.70!10"5

Correct

Part B The value of

for silver chromate,

, is

. Calculate the solubility of

in grams per liter.

Express your answer numerically in grams per liter.

Hint 1. Identify the

expression

The balanced equation for the complete dissociation of

is

What is the expression for the solubility product? ANSWER:

Hint 2. Express If

in terms of the molar solubility of

represents the number of moles per liter of

that dissolves to form a saturated solution, then we can construct the following

table:

excess

What is Express

0

0

+

+

in terms of in terms of

? .

ANSWER: =

Hint 3. Calculate the molar solubility of The solubility product is

. Calculate

Express the molar solubility numerically. ANSWER:

, the molar solubility of

.

= 1.31!10"4

Hint 4. Calculate the molar mass of Calculate the molar mass of

. Recall that you can access a periodic table by clicking the "Tools" link in the upper right corner of

the main question window. Express your answer numerically in grams per mole. ANSWER: molar mass of

= 332

ANSWER: solubility = 4.35!10"2

Correct When we know the solubility product for a substance, we can calculate its solubility, which is actually the concentration of a saturated solution. At 25 , the concentration of a saturated solution of silver chromate is or . If we add 10 of to 1 of water, only

of the salt will dissolve, and the rest will stay at the bottom of the beaker.

Score Summary: Your score on this assignment is 93.5%. You received 14.03 out of a possible total of 15 points.

Quiz 8

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