In this experiment, a student used a pH probe that was not properly calibrated. The probe reads the pH one unit higher than it should be. Would the calculated K, value of the unknown acid be higher or lower than the correct value? Justify your answer with an explanation.
In this experiment, a student used a pH probe that was not properly calibrated. The probe reads the pH one unit higher than it should be. Would the calculated K, value of the unknown acid be higher or lower than the correct value? Justify your answer with an explanation.
Chemistry
10th Edition
ISBN:9781305957404
Author:Steven S. Zumdahl, Susan A. Zumdahl, Donald J. DeCoste
Publisher:Steven S. Zumdahl, Susan A. Zumdahl, Donald J. DeCoste
Chapter1: Chemical Foundations
Section: Chapter Questions
Problem 1RQ: Define and explain the differences between the following terms. a. law and theory b. theory and...
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### Experiments in General Chemistry Featuring MeasureNet - Stanton et al.
**2.** In this experiment, a student used a pH probe that was not properly calibrated. The probe reads the pH one unit higher than it should be. Would the calculated \(K_a\) (acid dissociation constant) value of the unknown acid be higher or lower than the correct value? Justify your answer with an explanation.
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**Explanation:**
When a pH probe reads a value that is one unit higher than the actual pH, it indicates a higher concentration of hydrogen ions \((H^+)\) than is present. This incorrect reading will influence the calculation of the \(K_a\) value, which is derived from the equilibrium concentration of the acid and its ions in solution. Typically, \(K_a\) can be calculated from the equation:
\[ K_a = \frac{[H^+][A^-]}{[HA]} \]
where:
- \([H^+]\) is the concentration of hydrogen ions,
- \([A^-]\) is the concentration of the conjugate base,
- \([HA]\) is the concentration of the non-dissociated acid.
Given that the pH probe reads higher by one unit, it means the \([H^+]\) concentration is perceived to be lower than it truly is (since pH and \([H^+]\) are inversely related). In such a case, the calculated \([H^+]\) for \(K_a\) calculation will be lower, resulting in a lower \(K_a\) value.
The student must understand that the correct calibration of pH probes is crucial for accurate measurements in chemistry experiments. Calibration errors can significantly affect the quantification of a substance’s properties, such as the \(K_a\) value in this scenario.
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Transcribed Image Text:---
### Experiments in General Chemistry Featuring MeasureNet - Stanton et al.
**2.** In this experiment, a student used a pH probe that was not properly calibrated. The probe reads the pH one unit higher than it should be. Would the calculated \(K_a\) (acid dissociation constant) value of the unknown acid be higher or lower than the correct value? Justify your answer with an explanation.
---
**Explanation:**
When a pH probe reads a value that is one unit higher than the actual pH, it indicates a higher concentration of hydrogen ions \((H^+)\) than is present. This incorrect reading will influence the calculation of the \(K_a\) value, which is derived from the equilibrium concentration of the acid and its ions in solution. Typically, \(K_a\) can be calculated from the equation:
\[ K_a = \frac{[H^+][A^-]}{[HA]} \]
where:
- \([H^+]\) is the concentration of hydrogen ions,
- \([A^-]\) is the concentration of the conjugate base,
- \([HA]\) is the concentration of the non-dissociated acid.
Given that the pH probe reads higher by one unit, it means the \([H^+]\) concentration is perceived to be lower than it truly is (since pH and \([H^+]\) are inversely related). In such a case, the calculated \([H^+]\) for \(K_a\) calculation will be lower, resulting in a lower \(K_a\) value.
The student must understand that the correct calibration of pH probes is crucial for accurate measurements in chemistry experiments. Calibration errors can significantly affect the quantification of a substance’s properties, such as the \(K_a\) value in this scenario.
---
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