Student Solutions Manual for Bettelheim/Brown/Campbell/Farrell/Torres' Introduction to General, Organic and Biochemistry, 11th
Student Solutions Manual for Bettelheim/Brown/Campbell/Farrell/Torres' Introduction to General, Organic and Biochemistry, 11th
11th Edition
ISBN: 9781305081055
Author: Bettelheim, Frederick A.
Publisher: Cengage Learning
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Chapter 8, Problem 8.101P

8-101 Suppose you have an aqueous solution prepared by dissolving 0.050 mol of NaH2PO4 in 1 L of water. This solution is not a buffer, but suppose you want to make it into one. How many moles of solid Na2HPO4 must you add to this aqueous solution to make it into:

(a) A buffer of pH 7.21

(b) A buffer of pH 6.21

(c) A buffer of pH 8.21

Expert Solution
Check Mark
Interpretation Introduction

(a)

Interpretation:

The number of moles to be added in NaH2 PO4 to make it into a buffer of pH 6.21 should be calculated.

Concept Introduction:

The pH of buffer solution is calculated using the following formula:

 pH = pKa+ log[A][HA]

This is known as Henderson- Hasselbalch equation. Here, pKa is negative log of acid dissociation constant, [A] is concentration of conjugate base and [HA] is concentration of acid.

Answer to Problem 8.101P

0.050 mole of NaH2PO4.

Explanation of Solution

Given Information:

An aqueous solution contains 0.050 moles of NaH2 PO4.

The volume of the solution is 1 L.

The pH of the buffer solution is 7.21.

A buffer is a solution which resists change in pH when limited amounts of an acid or a base are added to it. The given buffer is made of the weak acid, NaH2 PO4 and its conjugate base Na2 HPO4.

The Henderson-Hasselbalch equation for a buffer of a weak acid (HA) and its conjugate base(A- ) is given as:

pH = pKa+ log[A][HA]

By using the Henderson-Hasselbalch equation for the pH of the buffer solution we get,

pH = pKa+ log[Na2HPO4][NaH2PO4]

As, we know that pKa of NaH2 PO4 is 7.21.

The volume of the buffer solution is 1 L. Assuming that there will not be any change in the volume of solution due to the addition of Na2 HPO4, the concentration terms in the Henderson-Hasselbalch equation can be replaced by the number of moles.

By substituting the values of pH, pKa and the number of moles of NaH2 PO4 for [NaH2 PO4 ] in the above equation, we get.

7.21 = 7.21+ log[Na2HPO4]0.0500=log[Na2HPO4]0.050

Bu taking antilog on both sides we get,

antilog(0) = [Na2HPO4]0.050             1 = [Na2HPO4]0.050[Na2HPO4] = 0.050

Thus, 0.050 moles of Na2 HPO4 must be added to the solution of NaH2 PO4 to make a buffer of 7.21. This also shows that when the equimolar of a weak acid and its conjugate base are taken, the pH of the buffer is equal to the pKa of the weak acid.

Expert Solution
Check Mark
Interpretation Introduction

(b)

Interpretation:

The number of moles to be added in NaH2 PO4 to make it into a buffer of pH 7.21 should be calculated.

Concept Introduction:

The pH of buffer solution is calculated using the following formula:

 pH = pKa+ log[A][HA]

This is known as Henderson- Hasselbalch equation. Here, pKa is negative log of acid dissociation constant, [A] is concentration of conjugate base and [HA] is concentration of acid.

Answer to Problem 8.101P

0.005 mole of NaH2PO4.

Explanation of Solution

Given Information:

An aqueous solution contains 0.050 moles of NaH2 PO4.

The volume of the solution is 1 L.

The pH of the buffer solution is 6.21.

By using the Henderson-Hasselbalch equation for the pH of the buffer solution we get,

pH = pKa+ log[Na2HPO4][NaH2PO4]

As, we know that pKa of NaH2 PO4 is 7.21.

The volume of the buffer solution is 1 L. Assuming that there will not be any change in the volume of solution due to the addition of Na2 HPO4, the concentration terms in the Henderson-Hasselbalch equation can be replaced by the number of moles.

By substituting the values of pH, pKa and the number of moles of NaH2 PO4 for [NaH2 PO4 ] in the above equation, we get.

6.21 = 7.21+ log[Na2HPO4]0.0501=log[Na2HPO4]0.050

Bu taking antilog on both sides we get,

antilog(-1.00) = [Na2HPO4]0.050                    1 = [Na2HPO4]0.050  [Na2HPO4] = 0.005

Thus, 0.005 moles of Na2 HPO4 must be added to the solution of NaH2 PO4 to make a buffer of 6.21.

Expert Solution
Check Mark
Interpretation Introduction

(c)

Interpretation:

The number of moles to be added in NaH2 PO4 to make it into a buffer of pH 8.21 should be calculated.

Concept Introduction:

The pH of buffer solution is calculated using the following formula:

 pH = pKa+ log[A][HA]

This is known as Henderson- Hasselbalch equation. Here, pKa is negative log of acid dissociation constant, [A] is concentration of conjugate base and [HA] is concentration of acid.

Answer to Problem 8.101P

0.500 mole of Na2HPO4.

Explanation of Solution

Given Information:

An aqueous solution contains 0.050 moles of NaH2 PO4.

The volume of the solution is 1 L.

The pH of the buffer solution is 8.21.

By using the Henderson-Hasselbalch equation for the pH of the buffer solution we get,

pH = pKa+ log[Na2HPO4][NaH2PO4]

As, we know that pKa of NaH2 PO4 is 7.21.

The volume of the buffer solution is 1 L. Assuming that there will not be any change in the volume of solution due to the addition of Na2 HPO4, the concentration terms in the Henderson-Hasselbalch equation can be replaced by the number of moles.

By substituting the values of pH, pKa and the number of moles of NaH2 PO4 for [NaH2 PO4 ] in the above equation, we get.

8.21 = 7.21+ log[Na2HPO4]0.0501.00=log[Na2HPO4]0.050

Bu taking antilog on both sides we get,

antilog(1.00) = [Na2HPO4]0.050                 10 = [Na2HPO4]0.050 [Na2HPO4] = 0.500

Thus, 0.500 moles of Na2 HPO4 must be added to the solution of NaH2 PO4 to make a buffer of 8.21.

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Chapter 8 Solutions

Student Solutions Manual for Bettelheim/Brown/Campbell/Farrell/Torres' Introduction to General, Organic and Biochemistry, 11th

Ch. 8.11 - Problem 8-11 What is the pH of a boric acid buffer...Ch. 8.12 - Prob. 8.12PCh. 8 - 8-13 Define (a) an Arrhenius acid and (b) an...Ch. 8 - 8-14 Write an equation for the reaction that takes...Ch. 8 - 8-15 Write an equation for the reaction that takes...Ch. 8 - 8-16 For each of the following, tell whether the...Ch. 8 - 8-17 For each of the following, tell whether the...Ch. 8 - 8-18 Which of these acids are monoprotic, which...Ch. 8 - 8-19 Define (a) a Brønsted—Lowry acid and (b) a...Ch. 8 - 8-20 Write the formula for the conjugate base of...Ch. 8 - 8-21 Write the formula for the conjugate base of...Ch. 8 - Prob. 8.22PCh. 8 - Prob. 8.23PCh. 8 - Prob. 8.24PCh. 8 - 8-25 Draw the acid and base reactions for the...Ch. 8 - Prob. 8.26PCh. 8 - Prob. 8.27PCh. 8 - 8-28 Will carbon dioxide be evolved as a gas when...Ch. 8 - Prob. 8.29PCh. 8 - Prob. 8.30PCh. 8 - Prob. 8.31PCh. 8 - Prob. 8.32PCh. 8 - 8-33 Write an equation for the reaction of HCI...Ch. 8 - 8-34 When a solution of sodium hydroxide is added...Ch. 8 - 8-35 Given the following values of [H3O+),...Ch. 8 - 8-36 Given the following values of [OH-],...Ch. 8 - 8-37 What is the pH of each solution given the...Ch. 8 - 8-38 What is the pH and pOH of each solution given...Ch. 8 - 8-39 What is the pH of each solution given the...Ch. 8 - Prob. 8.40PCh. 8 - 8-41 What is the [OH-] and pOH of each solution?...Ch. 8 - Prob. 8.42PCh. 8 - 8-43 What is the molarity of a solution made by...Ch. 8 - 8-44 What is the molarity of a solution made by...Ch. 8 - 8-45 Describe how you would prepare each of the...Ch. 8 - 8-46 If 25.0 mL of an aqueous solution of H2SO4...Ch. 8 - 8-47 A sample of 27.0 mL of 0.310 M NaOH is...Ch. 8 - 8-48 A 0.300 M solution of H2SO4 was used to...Ch. 8 - 8-49 A solution of NaOH base was titrated with...Ch. 8 - 8-50 The usual concentration of HCO3- ions in...Ch. 8 - 8-51 What is the end point of a titration?Ch. 8 - Prob. 8.52PCh. 8 - 8-53 Write equations to show what happens when, to...Ch. 8 - 8-54 Write equations to show what happens when, to...Ch. 8 - 8-55 We commonly refer to a buffer as consisting...Ch. 8 - Prob. 8.56PCh. 8 - Prob. 8.57PCh. 8 - 8-58 What is the connection between buffer action...Ch. 8 - Prob. 8.59PCh. 8 - 8-60 How is the buffer capacity affected by the...Ch. 8 - 8-61 Can 100 of 0.1 M phosphate buffer at pH 7.2...Ch. 8 - 8-62 What is the pH of a buffer solution made by...Ch. 8 - 8-63 The pH of a solution made by dissolving 1.0...Ch. 8 - Prob. 8.64PCh. 8 - Prob. 8.65PCh. 8 - 8-66 Calculate the pH of an aqueous solution...Ch. 8 - Prob. 8.67PCh. 8 - 8-68 If you have 100 mL of a 0.1 M buffer made of...Ch. 8 - Prob. 8.69PCh. 8 - Prob. 8.70PCh. 8 - 8-71 Explain why you do not need to know the...Ch. 8 - Prob. 8.72PCh. 8 - Prob. 8.73PCh. 8 - Prob. 8.74PCh. 8 - Prob. 8.75PCh. 8 - 8-76 (Chemical Connections 8B) Name the most...Ch. 8 - Prob. 8.77PCh. 8 - Prob. 8.78PCh. 8 - 8-79 (Chemical Connections 8D) Another form of the...Ch. 8 - Prob. 8.80PCh. 8 - Prob. 8.81PCh. 8 - 8-82 Assume that you have a dilute solution of HCI...Ch. 8 - Prob. 8.83PCh. 8 - Prob. 8.84PCh. 8 - Prob. 8.85PCh. 8 - 8-86 Following are three organic acids and the...Ch. 8 - 8-87 The pKavalue of barbituric acid is 5.0. If...Ch. 8 - Prob. 8.88PCh. 8 - Prob. 8.89PCh. 8 - Prob. 8.90PCh. 8 - Prob. 8.91PCh. 8 - Prob. 8.92PCh. 8 - 8-93 Do a 1.0 M CH3COOH solution and a 1.0 M HCI...Ch. 8 - 8-94 Suppose you wish to make a buffer whose pH is...Ch. 8 - Prob. 8.95PCh. 8 - 8-96 Suppose you want to make a CH3COOH/CH3COO-...Ch. 8 - Prob. 8.97PCh. 8 - 8-98 When a solution prepared by dissolving 4.00 g...Ch. 8 - Prob. 8.99PCh. 8 - Prob. 8.100PCh. 8 - 8-101 Suppose you have an aqueous solution...Ch. 8 - Prob. 8.102PCh. 8 - 8-103 Suppose you have a phosphate buffer...Ch. 8 - Prob. 8.104PCh. 8 - Prob. 8.105PCh. 8 - Prob. 8.106PCh. 8 - 8-107 Following are pH ranges for several human...Ch. 8 - 8-108 What is the ratio of HPO42-/H2PO4- in a...Ch. 8 - Prob. 8.109PCh. 8 - 8-110 A concentrated hydrochloric acid solution...Ch. 8 - 8-111 The volume of an adult's stomach ranges from...Ch. 8 - 8-112 Consider an initial 0.040 M hypobromous acid...Ch. 8 - Prob. 8.113PCh. 8 - Prob. 8.114PCh. 8 - 8-115 When a solution prepared by dissolving 0.125...Ch. 8 - 8-116 A railroad tank car derails and spills 26...Ch. 8 - Prob. 8.117P
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