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Chapter 16: Problem 39

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?

Short Answer

Expert verified
(a) The unknown solution is acidic. (b) The range of possible pH values for the solution is 4 to 6. (c) An alternative indicator is phenol red, which would help narrow down the pH range if the solution turns yellow when it is added.

Step by step solution

01

Recognizing the color changes for each indicator

Methyl orange changes its color from red (in acidic solution) to yellow (in basic solution) at the pH range of approximately 3.1 to 4.4. Bromthymol blue changes its color from yellow (in acidic solution) to blue (in basic solution) at the pH range of approximately 6.0 to 7.6. The given unknown solution shows a yellow color for both indicators.
02

Determining the pH range of the unknown solution and its acidity/basicity

Based on the information about the color changes of the indicators, when the unknown solution turns yellow for both methyl orange and bromthymol blue, it suggests that the pH of the solution is within the overlapping pH range for both indicators. The overlapping range for the two indicators is \(4.4 \leq pH \leq 6.0\). (a) Since the pH range of the solution is between 4.4 and 6.0, the unknown solution is acidic. (b) The range of possible pH values for the unknown solution is 4 to 6 in whole numbers.
03

Finding another indicator to narrow down the range of possible pH values

(c) An alternative indicator that can be used to narrow down the range of possible pH values is one that has a color change within the range of 4 to 6. An example is the indicator phenol red, which changes its color from yellow (in acidic solution) to red (in basic solution) at the pH range of approximately 6.4 to 8.0. By adding phenol red to the unknown solution, we would expect it to turn yellow if the pH of the solution is below 6.4, which would further narrow down the range of possible pH values for the unknown solution.

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Most popular questions from this chapter

Indicate whether each of the following statements is true or false. For each statement that is false, correct the statement to make it true. (a) Acid strength in a series of \(\mathrm{H}-\) A molecules increases with increasing size of \(\mathrm{A} .\) (b) For acids of the same general structure but differing electronegativities of the central atoms, acid strength decreases with increasing electronegativity of the central atom.(c) The strongest acid known is HF because fluorine is the most electronegative element.

(a) The hydrogen sulfite ion \(\left(\mathrm{HSO}_{3}^{-}\right)\) is amphiprotic. Write a balanced chemical equation showing how it acts as an acid toward water and another equation showing how it acts as a base toward water. (b) What is the conjugate acid of HSO \(_{3}^{-}?\) What is its conjugate base?

Deuterium oxide (\(\mathrm{D}_{2} \mathrm{O},\) 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.

(a) Which of the following is the stronger Bronsted-Lowry acid, \(\mathrm{HClO}_{3}\) or \(\mathrm{HClO}_{2} ?\) (b) Which is the stronger Bronsted-Lowry base, \(\mathrm{HS}^{-}\) or \(\mathrm{HSO}_{4}^{-}\) ?

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