Select the correct statement about this reaction: \[\begin{array} { l } \mathrm { CH } _ { 3 } \mathrm { CH } _ { 2 } \mathrm { SH } + { } ^ { - } \mathrm { CN } \rightleftarrows \mathrm { CH } _ { 3 } \mathrm { CH } _ { 2 } \mathrm {~S} ^ { - } + \mathrm { HCN } \\ \mathrm { p } K _ { \mathrm { a } } = 10.5 \\ p K _ { \mathrm { a } } = 9.4 \\ \end{array}\]

A) The equilibrium lies very far to the right. B) The equilibrium constant in the left-to-right direction is 1.1. C) The equilibrium constant in the left-to-right direction is 12.6. D) The equilibrium constant in the left-to-right direction is 0.08. E) The equilibrium constant in the left-to-right direction is −1.1. A) The equilibrium lies very far to the right. B) The equilibrium constant in the left-to-right direction is 1.1. C) The equilibrium constant in the left-to-right direction is 12.6. D) The equilibrium constant in the left-to-right direction is 0.08. E) The equilibrium constant in the left-to-right direction is −1.1.

Pentothal is a barbiturate used (as its sodium salt) as a short-acting anesthetic. Pentothal is a weak acid with a dissociation constant Ka = 4 × 10−8 M. Which one of the statements best describes the dissociation state of pentothal in the blood, which has a pH of 7.4?

A) more than 90% dissociated B) between 60% and 90% dissociated C) about half dissociated D) between 10% and 40% dissociated E) less than 10% dissociated A) more than 90% dissociated B) between 60% and 90% dissociated C) about half dissociated D) between 10% and 40% dissociated E) less than 10% dissociated

Exam 3: The Curved-Arrow Notation, Resonance, Acids and Bases, and Chemical Equilibrium

Complete the electron-pair displacement reaction by showing the curved arrows and the structure(s) of the product(s), including all charges and unshared valence electron pairs. Assume that phosphorus is the nucleophilic atom.

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Question 1

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The free energy of formation (ΔG_f°) is defined analogously to a heat of formation: it is the standard free energy for formation of a compound from its elements in their standard states at 298 K. Consider the following reaction and their associated standard free energies of formation (all in kJ mol⁻¹). Although these values are for the gas phase, they give us some idea of what to expect in solution. MTBE has been an important gasoline additive until it began to be replaced by ethanol in 2002. Calculate the equilibrium constant for this reaction in the left-to-right direction. Show your work.

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The ΔG° for the reaction is obtained by subtracting the ΔG_f° of the reactants from the ΔG_f° of the products. Thus,
ΔG° (reaction) = −293 − (−162.5 − 105.4) = −25.1 kJ mol⁻¹
ΔG° = −2.3RTlog K_eq
log K_eq = −ΔG°/2.3RT = −(−25.1)/5.7 = 4.4
K_eq = 10^4.4 or 2.53 × 10⁴ atm

Aspirin has the structure on the left with a pK_a of 3.4. $Aspirin has the structure on the left with a pKa of 3.4. a. Complete the structure on the right for the conjugate base of aspirin. b. In a large excess of stomach acid at pH = 2, calculate the fraction of aspirin that is ionized (to 2 significant figures).$ a. Complete the structure on the right for the conjugate base of aspirin. b. In a large excess of stomach acid at pH = 2, calculate the fraction of aspirin that is ionized (to 2 significant figures).

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a. The conjugate base of aspirin is formed by losing the acidic proton. The pK_a tells us that this is the carboxylic acid is the acidic group. The conjugate acid is the following anion:
$a. The conjugate base of aspirin is formed by losing the acidic proton. The pKa tells us that this is the carboxylic acid is the acidic group. The conjugate acid is the following anion: b. Calculate the fraction dissociated from the Henderson-Hasselbalch equation or, more easily, from Eq. 3.67a, with Δ = pH − pKa = 2 − 3.4 = −1.4. Therefore, aspirin is 3.8% ionized under these conditions. (If there is any doubt whether to use the equation with the Δ or −Δ in the denominator, we know that the fraction ionization is small because the pH is much lower than the pKa. Therefore, the second term in the denominator must be large.)$ b. Calculate the fraction dissociated from the Henderson-Hasselbalch equation or, more easily, from Eq. 3.67a, with Δ = pH − pK_a = 2 − 3.4 = −1.4.
$a. The conjugate base of aspirin is formed by losing the acidic proton. The pKa tells us that this is the carboxylic acid is the acidic group. The conjugate acid is the following anion: b. Calculate the fraction dissociated from the Henderson-Hasselbalch equation or, more easily, from Eq. 3.67a, with Δ = pH − pKa = 2 − 3.4 = −1.4. Therefore, aspirin is 3.8% ionized under these conditions. (If there is any doubt whether to use the equation with the Δ or −Δ in the denominator, we know that the fraction ionization is small because the pH is much lower than the pKa. Therefore, the second term in the denominator must be large.)$ Therefore, aspirin is 3.8% ionized under these conditions. (If there is any doubt whether to use the equation with the Δ or −Δ in the denominator, we know that the fraction ionization is small because the pH is much lower than the pK_a. Therefore, the second term in the denominator must be large.)

Give the products of the electron-pair displacement reaction. (Don't forget unshared pairs and formal charges.) Then circle the nucleophile.

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Question 4

Using curved arrows, show how each resonance structure is converted into the other.

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Question 5

Consider the acid-base equilibrium: a. What is the equilibrium constant K_eq for this reaction? b. In the above equation, circle the strongest base. c. On the left side of the equation, draw the curved arrows that show the formation of the products on the right.

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Question 6

Show the curved-arrow notation and the product (including all unshared valence electrons and formal charges, if any) for the Lewis acid-base association reaction of the two species. (Aluminum is in group 3A of the periodic table, beneath boron.) Then identify and label the nucleophile in the reaction.

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Question 7

Select the strongest acid.

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Question 8

Select the equilibrium that most favors products at equilibrium.

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Question 9

Choose the number that is closest to the equilibrium constant K_eq for this reaction:

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Question 10

Ascorbic acid (Vitamin C) is a diprotic acid with two pK_a values; pK_a1 = 4.2 and pK_a2 = 11.6. The two acidic groups are the two -OH groups, indicated by arrows in the structure. If we let AH₂ represent ascorbic acid, its successive ionized species can be abbreviated by ⁻AH and A²⁻. Draw the structure of ⁻AH and its two resonance structures. Draw the curved arrow notation to convert each structure to the next. (Hint: In one structure, charge is delocalized into the C=O group.)

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Question 11

The dissociation reaction for an acid has an associated standard free energy change (ΔG°_a) = 28.6 kJ mol⁻¹. What is the pK_a of the acid? (2.3RT at 298 K = 5.71 kJ mol⁻¹.)

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Question 12

Consider the Brønsted acid-base reaction: The equilibrium constant for this reaction is 250 (favorable to the right). What is the pKa of HCN (the acid on the right)?

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Question 13

In this acid-base equilibrium, the pK_a values of the two acids are 4.8 and 9.8, but you must decide which is which from your knowledge of approximate pK_a values. What is the equilibrium constant for this reaction?

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Question 14

Select the correct statement about this reaction: +\rightleftarrows+ =10.5 p=9.4

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Question 15

Draw curved arrows and give the products for an electron-pair displacement reaction in which hydroxide ion is the nucleophile and a carbon is the electrophile. Be sure to show all unshared electrons!

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Question 16

Select the equilibrium that lies farthest to the right.

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Question 17

Pentothal is a barbiturate used (as its sodium salt) as a short-acting anesthetic. Pentothal is a weak acid with a dissociation constant K_a = 4 × 10⁻⁸ M. Which one of the statements best describes the dissociation state of pentothal in the blood, which has a pH of 7.4?

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Question 18

Pivalic acid, which has the structure (CH₃)₃C-CO₂H, has a pK_a of 5.2. The standard free energy of ionization of pivalic acid is ________________ kJ mol⁻¹.

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Question 19

In the reaction, CH₃O⁻ acts as a nucleophile, the phosphorus as an electrophilic center, and CH₃S as a leaving group. (Don't be concerned that phosphorus has more than an octet of electrons-that's allowed, and it's irrelevant to the problem.) a. In the equation, draw the curved arrows for the process described. b. In the box, draw the products of the reaction. Don't forget formal charges.

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Question 20

Showing 1 - 20 of 25

Exam 3: The Curved-Arrow Notation, Resonance, Acids and Bases, and Chemical Equilibrium

Complete the electron-pair displacement reaction by showing the curved arrows and the structure(s) of the product(s), including all charges and unshared valence electron pairs. Assume that phosphorus is the nucleophilic atom.

Aspirin has the structure on the left with a pKa of 3.4. ​a. Complete the structure on the right for the conjugate base of aspirin. b. In a large excess of stomach acid at pH = 2, calculate the fraction of aspirin that is ionized (to 2 significant figures).

Give the products of the electron-pair displacement reaction. (Don't forget unshared pairs and formal charges.) Then circle the nucleophile.

Using curved arrows, show how each resonance structure is converted into the other.

Consider the acid-base equilibrium: a. What is the equilibrium constant Keq for this reaction? b. In the above equation, circle the strongest base. c. On the left side of the equation, draw the curved arrows that show the formation of the products on the right.

Select the strongest acid.

Select the equilibrium that most favors products at equilibrium.

Choose the number that is closest to the equilibrium constant Keq for this reaction:

The dissociation reaction for an acid has an associated standard free energy change (ΔG°a) = 28.6 kJ mol−1. What is the pKa of the acid? (2.3RT at 298 K = 5.71 kJ mol−1.)

Consider the Brønsted acid-base reaction: ​ The equilibrium constant for this reaction is 250 (favorable to the right). What is the pKa of HCN (the acid on the right)?

In this acid-base equilibrium, the pKa values of the two acids are 4.8 and 9.8, but you must decide which is which from your knowledge of approximate pKa values. What is the equilibrium constant for this reaction?

Select the correct statement about this reaction: +\rightleftarrows+ =10.5 p=9.4

Draw curved arrows and give the products for an electron-pair displacement reaction in which hydroxide ion is the nucleophile and a carbon is the electrophile. Be sure to show all unshared electrons!

Select the equilibrium that lies farthest to the right.

Pentothal is a barbiturate used (as its sodium salt) as a short-acting anesthetic. Pentothal is a weak acid with a dissociation constant Ka = 4 × 10−8 M. Which one of the statements best describes the dissociation state of pentothal in the blood, which has a pH of 7.4?

Pivalic acid, which has the structure (CH3)3C-CO2H, has a pKa of 5.2. The standard free energy of ionization of pivalic acid is ________________ kJ mol−1.

Chemical Bonding and Chemical Structure

Alkanes and Organic Nomenclature

Introduction to Alkenes and Alkynes

Addition Reactions of Alkenes and Alkynes

Principles of Stereochemistry

Cyclic Compounds and Reaction Stereochemistry

Nomenclature and Noncovalent Intermolecular Interactions

The Chemistry of Alkyl Halides

Free-Radical Reactions, Main-Group Organometallic Compounds, and Carbenes

The Chemistry of Alcohols and Thiols

The Chemistry of Ethers, Epoxides, Glycols, and Sulfides

Introduction to Spectroscopy

Nuclear Magnetic Resonance Spectroscopy

Dienes and Aromaticity

The Chemistry of Benzene and Its Derivatives

Allylic and Benzylic Reactivity

The Chemistry of Aryl Halides, Vinylic Halides, and Phenols

The Chemistry of Aldehydes and Ketones

The Chemistry of Carboxylic Acids

The Chemistry of Carboxylic Acid Derivatives

The Chemistry of Enolate Ions, Enols, and Α,β-Unsaturated Carbonyl Compounds

The Chemistry of Amines

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The Chemistry of Thioesters, Phosphate Esters, and Phosphate Anhydrides

The Chemistry of the Aromatic Heterocycles and Nucleic Acids

Amino Acids, Peptides, and Proteins

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Consider the acid-base equilibrium: a. What is the equilibrium constant K_eq for this reaction? b. In the above equation, circle the strongest base. c. On the left side of the equation, draw the curved arrows that show the formation of the products on the right.

Choose the number that is closest to the equilibrium constant K_eq for this reaction:

The dissociation reaction for an acid has an associated standard free energy change (ΔG°_a) = 28.6 kJ mol⁻¹. What is the pK_a of the acid? (2.3RT at 298 K = 5.71 kJ mol⁻¹.)

Consider the Brønsted acid-base reaction: The equilibrium constant for this reaction is 250 (favorable to the right). What is the pKa of HCN (the acid on the right)?

In this acid-base equilibrium, the pK_a values of the two acids are 4.8 and 9.8, but you must decide which is which from your knowledge of approximate pK_a values. What is the equilibrium constant for this reaction?

Pentothal is a barbiturate used (as its sodium salt) as a short-acting anesthetic. Pentothal is a weak acid with a dissociation constant K_a = 4 × 10⁻⁸ M. Which one of the statements best describes the dissociation state of pentothal in the blood, which has a pH of 7.4?

Pivalic acid, which has the structure (CH₃)₃C-CO₂H, has a pK_a of 5.2. The standard free energy of ionization of pivalic acid is ________________ kJ mol⁻¹.