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Indicator PH Range Color Change

This document provides instructions and questions for a pre-lab and post-lab assignment on measuring pH and preparing buffer solutions. The pre-lab asks students to define pH and buffer related terms, explain the importance of pH in biology, define the Henderson-Hasselbalch equation, and list pH ranges and color changes for common pH indicators. It also asks how buffer concentration is determined and to show sample calculations for preparing an assigned buffer solution. The post-lab asks students to explain potential discrepancies in calculated vs measured pH, the need to calibrate pH meters, advantages of electrometric over colorimetric pH measurement, effects of dilution on buffer pH and capacity, and to calculate the pH of a mixed buffer solution.

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227 views2 pages

Indicator PH Range Color Change

This document provides instructions and questions for a pre-lab and post-lab assignment on measuring pH and preparing buffer solutions. The pre-lab asks students to define pH and buffer related terms, explain the importance of pH in biology, define the Henderson-Hasselbalch equation, and list pH ranges and color changes for common pH indicators. It also asks how buffer concentration is determined and to show sample calculations for preparing an assigned buffer solution. The post-lab asks students to explain potential discrepancies in calculated vs measured pH, the need to calibrate pH meters, advantages of electrometric over colorimetric pH measurement, effects of dilution on buffer pH and capacity, and to calculate the pH of a mixed buffer solution.

Uploaded by

superbawang321
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as DOCX, PDF, TXT or read online on Scribd
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PRE-LAB

pH Measurement and Buffer Preparation

Name: Group No.:

Section: 2G-PH Date Submitted: Sept. 4, 2020

1. Differentiate the following:


a. pH from pOH

b. Ka from Kb

c. pKa from pKb

d. Kw from pKw

e. Molarity from normality

2. Why are pH and buffer important in biological systems?

3. What is the Henderson-Hasselbalch equation?

4. What are the approximate pH ranges and color changes of the following organic dyes?

Indicator pH Range Color Change


Thymol blue (acid range)
Bromophenol blue
Bromocresol green
Bromocresol purple
Phenol red
Thymol blue (alkaline range)
Methyl red – Methylene blue
Methyl orange
Phenolphtalein

5. How is the concentration of a buffer solution determined?

6. How is the assigned buffer prepared? Write computation. Encircle the amount of solute needed
for the preparation.
POST-LAB
pH Measurement and Buffer Preparation

Name: Group No.:

Section: 2G-PH Date Submitted:

1. Why is there a discrepancy between the calculated pH and the experimental pH of a prepared
buffer solution?

2. Why is it necessary to calibrate the pH meter?

3. Why is the electrometric method of pH determination more accurate than the colorimetric
method?

4. What is the effect of dilution on the pH of a buffer and the buffer’s capacity?

5. A solution is prepared by mixing 80mL of 0.2M KH 2PO4 and 120mL of 0.2M K2HPO4. What is its
pH?

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