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18. Aqueous Equilibrium

Acid-Base Indicators

18. Aqueous Equilibrium

Acid-Base Indicators

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Acid-Base Indicator

Acid-Base Indicator

Acid-Base Indicators Example

Acid-Base Indicators Example

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Multiple Choice

Chemistry student is using an indicator with a pK_a of 4.7 for the titration of a strong acid with strong base. Calculate the pH range at which the indicator will change colors.

a) 2.7–3.5 b) 10–11 c) 4.7–8.7 d) 3.7–5.7 e) 2.7–5.8

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Multiple Choice

Bromophenol blue (pK_a = 4.1) is a common acid-base indicator. It is yellow in its acidic form and blue in conjugate base form. If the solution being titrated has a pH = 4.0, what color would the bromophenol blue indicator possess?

a) yellow b) orange c) blue d) green e) purple

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Textbook Question

The beaker on the right contains 0.1 M acetic acid solution with methyl orange as an indicator. The beaker on the left contains a mixture of 0.1 M acetic acid and 0.1 M sodium acetate with methyl orange. (a) Using Figures 16.8 and 16.9, which solution has a higher pH?

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Textbook Question

The indicator methyl orange has been added to both of the following solutions. Based on the colors, classify each statement as true or false: (a) The pH of solution A is definitely less than 7.00.

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Textbook Question

You are titrating an acidic solution with a basic one, and just realized you forgot to add the indicator that tells you when the equivalence point is reached. In this titration, the indicator turns blue at the equivalence point from an initially colorless solution. You quickly grab a bottle of indicator and add some to your titration beaker, and the whole solution turns dark blue. What do you do now?

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Textbook Question

Addition of the indicator methyl orange to an unknown solution leads to a yellow color. The addition of bromthymol blue to the same solution also leads to a yellow color. (b) What is the range (in whole numbers) of possible pH values for the solution?

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Textbook Question

Addition of phenolphthalein to an unknown colorless solution does not cause a color change. The addition of bromthymol blue to the same solution leads to a yellow color. (c) What other indicator or indicators would you want to use to determine the pH of the solution more precisely?

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Textbook Question

Addition of phenolphthalein to an unknown colorless solution does not cause a color change. The addition of bromthymol blue to the same solution leads to a yellow color. (b) Which of the following can you establish about the solution: (i) A minimum pH, (ii) A maximum pH, or (iii) A specific range of pH values?

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Textbook Question

Which of the indicators given in Figure 16.5, methyl violet, bromcresol green, phenol red, or thymolphthalein, would be most appropriate to detect a pH change from: (c) 2 to 0?

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Textbook Question

Which of the indicators given in Figure 16.5, methyl violet, bromcresol green, phenol red, or thymolphthalein, would be most appropriate to detect a pH change from: (b) 8 to 10?

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Textbook Question

Methyl red has a pKa of 5.0 and is red in its acid form and yellow in its basic form. If several drops of this indicator are placed in a 25.0-mL sample of 0.100 M HCl, what color will the solution appear? If 0.100 M NaOH is slowly added to the HCl sample, in what pH range will the indicator change color?

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Textbook Question

Referring to Table 17.1, pick an indicator for use in the titration of each acid with a strong base. a. HF

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Textbook Question

Referring to Table 17.1, pick an indicator for use in the titration of each base with a strong acid. a. CH3NH2

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Textbook Question

The acid–base indicator bromcresol green is a weak acid. The yellow acid and blue base forms of the indicator are present in equal concentrations in a solution when the pH is 4.68. What is the pKa for bromcresol green?

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Textbook Question

A 40.0 mL sample of a mixture of HCl and H3PO4 was titrated with 0.100 M NaOH. The first equivalence point was reached after 88.0 mL of base, and the second equiva-lence point was reached after 126.4 mL of base. (f) What indicators would you select to signal the equiva-lence points?

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When CO₂ combines with water it forms carbonic acid. How does this explain the phenol red result?

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A substance that changes color in the presence of an acid or base is called a(n)

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