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Holt Chemistry

R.Thomas Myers, Keith Oldham,Savatore Tocci

Chapter 15

Acids and Bases

Educators


Problem 1

How does a strong acid differ from a weak acid?

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Problem 2

What kind of an electrolyte is a weak base?

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Problem 3

How does Bronsted and Lowry's definition of an acid differ from Arrhenius's definition of an acid? Explain which definition is broader.

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Problem 4

What is the conjugate acid of the base ammonia, $\mathrm{NH}_{3}$ ?

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Problem 5

Why is water considered amphoteric?

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Problem 6

What is the concentration of hydroxide ions in pure water?

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Problem 7

What is the value of $K_{w}$ at $25^{\circ} \mathrm{C} ?$

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Problem 8

What is the pH of a neutral solution?

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Problem 9

Give the equation that relates pH to hydronium ion concentration.

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Problem 10

How does the strength of an acid relate to the concentration of the acid? How does the strength of an acid relate to the pH of an aqueous solution of the acid? How does the concentration of an acid solution relate to the solution's pH?

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Problem 11

What product do all neutralization reactions have in common?

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Problem 12

At what point in a titration are the amounts of hydronium ions and hydroxide ions equal?

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Problem 13

Group the following four terms into two pairs according to how the terms are related, and explain how they are related: end point, standard solution, titrant, and transition range.

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Problem 14

What is the equilibrium constant that is applied to a weak acid?

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Problem 15

How does the addition of a small amount of acid or base affect a buffered solution?

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Problem 16

Compare the properties of an acid with those of a base.

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Problem 17

What is a base according to Arrhenius? according to Bronsted and Lowry?

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Problem 18

Why are weak acids and weak bases poor electrical conductors?

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Problem 19

What is the difference between the strength and the concentration of an acid?

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Problem 20

Identify each of the following compounds as an acid or a base according to the Bronsted-Lowry classification. For each species, write the formula and the name of its conjugate.
\begin{equation}
\begin{array}{l}{\text { a. } \mathrm{CH}_{3} \mathrm{COO}^{-}} \\ {\text { b. HCN }} \\ {\text { c. HOOCCOOH }} \\ {\text { d. } C_{6} \mathrm{H}_{5} \mathrm{NH}_{3}^{+}}\end{array}
\end{equation}

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Problem 21

Write an equation for the reaction between hydrocyanic acid, HCN, and water. Label the acid, base, conjugate acid, and conjugate base.

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Problem 22

Write chemical equations that show how the hydrogen carbonate ion, HCO $_{3}^{-}$ acts as an amphoteric ion.

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Problem 23

Explain the relationship between the self-ionization of water and $K_{w}$ .

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Problem 24

Write an equation that shows the self-ionization of water.

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Problem 25

Three solutions have pHs of $3,7,$ and $11 .$ Which solution is basic? Which is acidic? Which is neutral?

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Problem 26

By what factor does $\left[\mathrm{OH}^{-}\right]$ change when the $\mathrm{pH}$ increases by 3$?$ by 2$?$ by 1 ? by 0.5$?$

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Problem 27

Explain how you can calculate pH from $\left[\mathrm{H}_{3} \mathrm{O}^{+}\right]$ by using your calculator.

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Problem 28

Describe two methods of measuring pH, and explain the advantages and disadvantages of each method.

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Problem 29

What is a neutralization reaction?

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Problem 30

Describe two precautions that should be taken to ensure an accurate titration.

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Problem 31

Explain what a titration curve is, and sketch its shape.

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Problem 32

How would you select an indicator for a particular acid-base titration?

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Problem 33

Would the $\mathrm{pH}$ at the equivalence point of a titration of a weak acid with a strong base be less than, equal to, or greater than 7.0$?$

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Problem 34

Name an indicator you might use to titrate ammonia with hydrochloric acid.

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Problem 35

The $K_{a}$ of nitrous acid, $\mathrm{HNO}_{2},$ is $6.76 \times 10^{-4} .$ Write the equation describing the equilibrium established when $\mathrm{HNO}_{2}$ reacts with $\mathrm{NH}_{3} .$ Use unequal arrows to indicate whether reactants or products are favored.

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Problem 36

$\begin{array}{l}{\text { a. What is the relationship between the }} \\ {\text { strength of an acid and the strength of }} \\ {\text { its conjugate base? }} \\ {\text { b. What is the realtionship between the }} \\ {\text { strength of a base and the strenght of }} \\ {\text { its conjugate acid? }}\end{array}$

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Problem 37

Propanoic acid, $\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{COOH},$ is a weak acid. Write the expression defining its acid-ionization constant.

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Problem 38

Place the following acids in order of increasing strength:
\begin{equation}
\begin{array}{l}{\text { a. valeric acid, } K_{a}=1.5 \times 10^{-5}} \\ {\text { b. glutaric acid, } K_{a}=3.4 \times 10^{-4}} \\ {\text { c. hypoobromous acid, } K_{a}=2.5 \times 10^{-9}} \\ {\text { d. acetylsalicylic acid (aspirin), }} \\ {K_{a}=3.3 \times 10^{-4}}\end{array}
\end{equation}

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Problem 39

What are the components of a buffer solution? Give an example.

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Problem 40

If the hydronium ion concentration of a solution is $1.63 \times 10^{-8} \mathrm{M},$ what is the hydroxide ion concentration?

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Problem 41

Calculate the hydronium ion concentration in a solution of 0.365 $\mathrm{mol} / \mathrm{L}$ of $\mathrm{NaOH} .$

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Problem 42

How much $\mathrm{HCl}$ would you need to dissolve in 1.0 $\mathrm{L}$ of water so that $\left[\mathrm{OH}^{-}\right]=$ $6.0 \times 10^{-12} \mathrm{M} ?$

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Problem 43

The hydronium ion concentration in a solution is $1.87 \times 10^{-3}$ mol/L. What is $\left[\mathrm{OH}^{-}\right]$ ?

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Problem 44

If 0.150 mol of $\mathrm{KOH}$ is dissolved in 500 $\mathrm{mL}$ of water, what are $\left[\mathrm{OH}^{-}\right]$ and $\left[\mathrm{H}_{3} \mathrm{O}^{+}\right]$ ?

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Problem 45

If a solution contains twice the concentration of hydronium ions as hydroxide ions, what is the hydronium ion concentration?

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Problem 46

Stomach acid contains $\mathrm{HCl}$ , whose concentration is about 0.03 $\mathrm{mol} / \mathrm{L} .$ What is the pH of stomach acid?

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Problem 47

If $\left[\mathrm{OH}^{-}\right]$ of an aqueous solution is $0.0134 \mathrm{mol} / \mathrm{L},$ what is the pH?

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Problem 48

What is the pH of a 0.15 $\mathrm{M}$ solution of $\mathrm{HClO}_{4}, \mathrm{a}$ strong acid?

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Problem 49

LiOH is a strong base. What is the pH of a 0.082 M LiOH solution?

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Problem 50

Find the $\mathrm{pH}$ of a solution consisting of 0.29 mol of $\mathrm{HBr}$ in 1.0 $\mathrm{L}$ of water.

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Problem 51

What is the $\mathrm{pH}$ of aqueous solutions of the strong acid $\mathrm{HNO}_{3},$ nitric acid, if the concentrations of the solutions are as follows: (a) $0.005 \mathrm{M},(\mathrm{b}) 0.05 \mathrm{M},(\mathrm{c}) 0.5 \mathrm{M},(\mathrm{d}) 5 \mathrm{M} ?$

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Problem 52

Find the $\mathrm{pH}$ of a solution prepared by dissolving 0.65 $\mathrm{mol}$ of the strong base $\mathrm{NaOH}$ in 1.0 $\mathrm{L}$ of water.

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Problem 53

What is the $\mathrm{pH}$ of a solution prepared by dissolving 0.15 $\mathrm{mol}$ of the strong base $\mathrm{Ba}(\mathrm{OH})_{2}$ in one liter of water? (Hint: How much hydroxide ion does barium hydroxide generate per mole in solution?)

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Problem 54

A solution has a hydronium ion concentration of $1.0 \times 10^{-9} \mathrm{M} .$ What is its pH?

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Problem 55

If a solution has a hydronium ion concentration of $6.7 \times 10^{-1} \mathrm{M},$ what is its pH?

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Problem 56

What is the $\mathrm{pH}$ of a solution whose hydronium ion concentration is $2.2 \times 10^{-12} \mathrm{M} ?$

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Problem 57

What is the pH of a solution whose $\mathrm{H}_{3} \mathrm{O}^{+}$ concentration is $1.9 \times 10^{-6} \mathrm{M} ?$

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Problem 58

Calculate the $\mathrm{pH}$ of a 0.0316 $\mathrm{M}$ solution of the strong base RbOH.

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Problem 59

The pH of a solution is $9.5 .$ What is $\left[\mathrm{H}_{3} \mathrm{O}^{+}\right]$ ? What is $\left[\mathrm{OH}^{-}\right] ?$

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Problem 60

A solution of a weak acid has a pH of $4.7 .$ What is the hydronium ion concentration?

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Problem 61

A 50 $\mathrm{mL}$ sample of apple juice has a pH of $3.2 .$ What amount, in moles, of $\mathrm{H}_{3} \mathrm{O}^{+}$ is present?

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Problem 62

Find $\left[\mathrm{H}_{3} \mathrm{O}^{+}\right]$ in a solution of $\mathrm{pH} 4$.

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Problem 63

What is the hydroxide ion concentration in a solution of $\mathrm{pH} 8.72 ?$

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Problem 64

Calculate the concentration of the $\mathrm{H}_{3} \mathrm{O}^{+}$ and $\mathrm{OH}^{-}$ ions in an aqueous solution of pH $5.0 .$

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Problem 65

A solution has a pH of $10.1 .$ Calculate the hydronium ion concentration and the hydroxide ion concentration.

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Problem 66

What is the hydronium ion concentration in a solution of pH 5.5?

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Problem 67

If the pH of a solution is $4.3,$ what is the hydroxide ion concentration?

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Problem 68

What is the hydronium ion concentration in a solution whose pH is 10.0$?$

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Problem 69

The pH of a solution is $3.0 .$ What is $\left[\mathrm{H}_{3} \mathrm{O}^{+}\right] ?$

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Problem 70

What is $\left[\mathrm{H}_{3} \mathrm{O}^{+}\right]$ in a solution whose pH is 1.9$?$

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Problem 71

If a solution has a pH of 13.3, what is its hydronium ion concentration?

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Problem 72

To what volumetric mark should a buret be filled?

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Problem 73

Why is it important to slow down the drop rate of the buret near the end of a titration?

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Problem 74

What two buret readings need to be recorded in order to determine the volume of solution dispensed by the buret?

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Problem 75

What volume of 0.100 $\mathrm{M} \mathrm{NaOH}$ is required to neutralize 25.00 $\mathrm{mL}$ of 0.110 $\mathrm{M} \mathrm{H}_{2} \mathrm{SO}_{4} ?$

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Problem 76

What volume of 0.100 $\mathrm{M} \mathrm{NaOH}$ is required to neutralize 25.00 $\mathrm{mL}$ of 0.150 $\mathrm{M} \mathrm{HCl}$ ?

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Problem 77

If 35.40 $\mathrm{mL}$ of 1.000 $\mathrm{M} \mathrm{HCl}$ is neutralized by 67.30 mL of NaOH, what is the molarity of the NaOH solution?

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Problem 78

If 50.00 $\mathrm{mL}$ of 1.000 $\mathrm{M} \mathrm{HI}$ is neutralized by 35.41 $\mathrm{mL}$ of $\mathrm{KOH}$ , what is the molarity of the $\mathrm{KOH}$ solution?

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Problem 79

If 133.73 $\mathrm{mL}$ of a standard solution of $\mathrm{KOH}$ , of concentration $0.298 \mathrm{M},$ exactly neutralized 50.0 $\mathrm{mL}$ of an acidic solution, what was the acid concentration?

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Problem 80

To standardize a hydrochloric acid solution, it was used as titrant with a solid sample of sodium hydrogen carbonate, NaHCO $_{3} .$ The sample had a mass of $0.3967 \mathrm{g},$ and 41.77 $\mathrm{mL}$ of acid was required to reach the equivalence point. Calculate the concentration of
the standard solution.

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Problem 81

The graph above shows a titration curve obtained during the titration of a 25.00 $\mathrm{mL}$ sample of an acid with 0.1000 $\mathrm{M} \mathrm{NaOH} .$ Calculate the concentration of the acid.

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Problem 82

An HNO $_{3}$ solution has a pH of $3.06 .$ What volume of 0.015 $\mathrm{M}$ LiOH will be required to titrate 65.0 $\mathrm{mL}$ of the HNO $_{3}$ solution to reach the equivalence point?

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Problem 83

The hydronium ion concentration in a 0.100 M solution of formic acid is 0.0043 $\mathrm{M}$ . Calculate $K_{a}$ for formic acid.

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Problem 84

$\left[\mathrm{NO}_{2}^{-}\right]=9.1 \times 10^{-3} \mathrm{mol} / \mathrm{L}$ in a nitrous acid
solution of concentration 0.123 $\mathrm{mol} / \mathrm{L}$ What is $K_{a}$ for $\mathrm{HNO}_{2}$ ?

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Problem 85

A solution of acetic acid had the following solute concentrations: $\left[\mathrm{CH}_{3} \mathrm{COOH}\right]=$ $0.035 \mathrm{M},\left[\mathrm{H}_{3} \mathrm{O}^{+}\right]=7.4 \times 10^{-4} \mathrm{M},$ and $\left[\mathrm{CH}_{3} \mathrm{COO}^{-}\right]=7.4 \times 10^{-4} \mathrm{M} .$ Calculate the $K_{a}$ of acetic acid based on these data.

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Problem 86

Hydrazoic acid, HN $_{3},$ is a weak acid. A 0.01 M solution of hydrazoic acid contained a concentration of 0.0005 $\mathrm{M}$ of the $\mathrm{N}_{3}^{-}$ ion. Find the acid-ionization constant of hydrazoic acid.

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Problem 87

If 25 $\mathrm{mL}$ of 1.00 $\mathrm{M} \mathrm{HCl}$ is mixed with 75 $\mathrm{mL}$ of $1.00 \mathrm{M} \mathrm{NaOH},$ what are the final amounts and concentrations of all ions present?

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Problem 88

When 1.0 $\mathrm{mol}$ of a weak acid was dissolved in 10.0 L of water, the pH was found to be $3.90 .$ What is $K_{a}$ for the acid?

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Problem 89

At the end point of a titration of 25 $\mathrm{mL}$ of 0.300 $\mathrm{M} \mathrm{NaOH}$ with $0.200 \mathrm{M} \mathrm{HNO}_{3},$ what would the concentration of sodium nitrate in the titration flask be?

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Problem 90

Make a table listing the ionic concentrations in solutions of the following pH values: $14.25,14.00,13.75,13.25,13.00,7.25,7.00$ $6.75,1.00,0.75,0.50,0.25,0.00,$ and $-0.25$

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Problem 91

Write the equilibrium equation and the equilibrium constant expression for an ammonia-ammonium ion buffer solution.

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Problem 92

If 18.5 $\mathrm{mL}$ of a 0.0350 $\mathrm{M} \mathrm{H}_{2} \mathrm{SO}_{4}$ solution neutralizes 12.5 $\mathrm{mL}$ of aqueous LiOH, what mass of LiOH was used to make 1.00 $\mathrm{L}$ of the LiOH solution?

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Problem 93

Use Table 7 to calculate the pH of a buffer solution made from equal amounts of sodium monohydrogen phosphate and potassium dihydrogen phosphate.

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Problem 94

Why is a buret, rather than a graduated cylinder, used in titrations?

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Problem 95

A small volume of indicator solution is usually added to the titration flask right before the titration. As a result, the sample is diluted slightly. Does this matter? Why or why not?

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Problem 96

A student passes an end point in a titration. Is it possible to add an additional measured amount of the unknown and continue the titration? Explain how this process might work. How would the answer for the calculation of the molar concentration of the unknown differ from the answer the student would have gotten if the titration had been performed properly?

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Problem 97

Refer to the table above to answer the following questions:
\begin{equation}
\begin{array}{l}{\text { a. Which indicator would be the best choice }} \\ {\text { for a titration with an end point at a pH }} \\ {\text { of } 4.0 ?} \\ {\text { b. Which indicators would work best for a }} \\ {\quad \text { titration of a weak base with a strong acid? }}\end{array}
\end{equation}

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Problem 98

Why does an indicator need to be a weak acid or a weak base?

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Problem 99

Explain the difference between end point and equivalence point. Why is it important that both occur at approximately the same pH in a titration?

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Problem 100

Can you neutralize a strong acid solution by adding an equal volume of a weak base having the same molarity as the acid? Support your position.

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Problem 101

In the 18 th century, Antoine Lavoisier experimented with oxides such as $\mathrm{CO}_{2}$ and
$\mathrm{SO}_{2} .$ He observed that they formed acidic solutions. His observations led him to infer that for a substance to exhibit acidic behavior, it must contain oxygen. However, today that is known to be incorrect. Provide evidence to refute Lavoisier's conclusion.

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Problem 102

Design an experiment to test the neutralization effectiveness of various brands of antacid. Show your procedure, including all safety procedures and cautions, to your teacher for approval. If your teacher approves your plan, carry it out. After experimenting, write an advertisement for the antacid you judge to be the most effective. Cite data from your experiments as part of your advertising claims.

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Problem 103

Describe how you would prepare one or more buffer solutions, including which compounds to use. Predict the pH of each solution. If your teacher provides the needed materials, measure the pH to test
your prediction.

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Problem 104

Use the following terms to create a concept map: hydronium ions $\left(H_{3} O^{+}\right),$ hydroxide
ions $\left(O H^{-}\right)$ , neutralization reaction, pH, and titration.

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Problem 105

What variable is being measured along the $x$ -axis?

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Problem 106

What is the $\mathrm{pH}$ at the beginning of the titration?

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Problem 107

What was the $\mathrm{pH}$ after 25 $\mathrm{mL}$ of titrant had been added?

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Problem 108

What volume of titrant was needed to reach a pH of 2.0$?$

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Problem 109

Where on the graph do you find the single most important data point?

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Problem 110

If the titration continued beyond what the graph shows, how would you expect the pH to change past the end of the graph?

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Problem 111

Roughly sketch the titration curve $(\mathrm{pH}$ versus volume) that you would expect if you titrated a weak base with a strong acid. Mark the equivalence point.

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Problem 112

Graphing Calculator
Graphing Titration Data The graphing calculator can run a program that graphs data such as pH versus volume of base. Graphing the titration data will allow you to determine which combination of acid and base is represented by the shape of the graph.

Go to Appendix C. If you are using a TI-83 Plus, you can download the program and data and run the application as directed. Press the APPS key on your calculator, then choose the application CHEMAPS. Press 5 , then highlight ALL on the screen, press 1 , then highlight LOAD and press 2 to load the data into your calculator. Quit the application, and then run the program TITRATN. For $\mathrm{L}_{1},$ press 2 $\mathrm{nd}$ and $\mathrm{LIST},$ and choose VOL 1. For $\mathrm{L}_{2},$ press 2 nd and LIST and choose PH1. If you are using another calculator, your
teacher will provide you with keystrokes and data sets to use.
\begin{equation}
\begin{array}{l}{\text { a. At what approximate volume does the }} \\ {\text { pH change from acidic to basic? }} \\ {\text { b. If the titrant was } 0.24 \mathrm{M} \mathrm{NaOH} \text { , and the }} \\ {\text { volume of unknown was } 230 \mathrm{mL}, \text { what }} \\ {\text { was }\left[\mathrm{H}_{3} \mathrm{O}^{+}\right] \text { in the unknown solution? }}\end{array}
\end{equation}

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