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Chapter 16: Problem 40

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. (a) Is the solution acidic, neutral, or basic? (b) Which of the following can you establish about the solution: (i) A minimum \(\mathrm{pH}\), (ii) A maximum \(\mathrm{pH}\), or (iii) A specific range of pH values? (c) What other indicator or indicators would you want to use to determine the \(\mathrm{pH}\) of the solution more precisely?

Short Answer

Expert verified
(a) The solution is acidic as the pH is below 6.0. (b) (i) Insufficient information is available to infer the minimum pH value. (ii) The maximum pH of the solution is 6.0. (iii) We cannot determine the specific range of pH values without additional information. (c) To determine the pH more precisely, litmus paper (range 4.5-8.3, red to blue) or methyl orange (range 3.2-4.4, red to yellow) can be used as indicators.

Step by step solution

01

(a) Determine the solution's nature (acidic, neutral, or basic)

Given that phenolphthalein did not cause any color change, it confirms that the pH of the solution is below 8.2. On the other hand, bromthymol blue turned the solution yellow, meaning the pH of the solution must be below 6.0. Considering both indicators, the unknown solution must have a pH below 6.0. As a result, the solution is acidic.
02

(b) (i) Determine the minimum \(\mathrm{pH}\)

Since the given indicators did not reach a lower bound, there is insufficient information to infer the minimum pH value for the unknown solution.
03

(b) (ii) Determine the maximum \(\mathrm{pH}\)

Bromthymol blue displayed a yellow color which indicates that the pH is less than 6.0. Hence, the maximum pH of the solution is 6.0.
04

(b) (iii) Determine the specific range of pH values

In this case, the indicators provide us with partial information on the range of pH values. The solution's pH is less than 6.0, but we cannot determine the specific range of pH values without additional information.
05

(c) Choosing other indicator or indicators

To determine the pH of the solution more precisely within the acidic range, indicators with a color change range that covers lower pH values are required. Some examples include litmus paper, which has a color change range between 4.5-8.3 (red to blue), or methyl orange, with a pH change range between 3.2-4.4 (red to yellow).

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Most popular questions from this chapter

Deuterium oxide \(\left(\mathrm{D}_{2} \mathrm{O},\right.\) where \(\mathrm{D}\) is deuterium, the hydrogen- 2 isotope) has an ion-product constant, \(K_{w}\), of \(8.9 \times 10^{-16}\) at \(20^{\circ} \mathrm{C}\). Calculate \(\left[\mathrm{D}^{+}\right]\) and \(\left[\mathrm{OD}^{-}\right]\) for pure (neutral) \(\mathrm{D}_{2} \mathrm{O}\) at this temperature.

By what factor does \(\left[\mathrm{H}^{+}\right]\) change for a pH change of (a) 3.0 units, (b) 0.3 units?

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. (a) Is the solution acidic, neutral, or basic? (b) What is the range (in whole numbers) of possible pH values for the solution? (c) Is there another indicator you could use to narrow the range of possible pH values for the solution?

(a) Write an equation for the react ion in which \(\mathrm{HSO}_{4}^{-}(a q)\) acts as a base in \(\mathrm{H}_{2} \mathrm{O}(l) .(\mathbf{b})\) Write an equation for the reaction in which \(\mathrm{HSO}_{4}^{-}(a q)\) acts as an acid in \(\mathrm{H}_{2} \mathrm{O}(I) \cdot(\mathbf{c})\) What is the conjugate acid of \(\mathrm{HSO}_{4}^{-}(a q) ?\) What is its conjugate base?

Which member of each pair produces the more acidic aqueous solution: \((\mathbf{a}) \mathrm{Zn} \mathrm{Br}_{2}\) or \(\mathrm{CdCl}_{2},\) (b) \(\mathrm{CuCl}\) or \(\mathrm{Cu}\left(\mathrm{NO}_{3}\right)_{2}\), (c) \(\mathrm{Ca}\left(\mathrm{NO}_{3}\right)_{2}\) or \(\mathrm{NiBr}_{2} ?\)
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