1. What is the purpose of calibrating a pH meter? 2. For the first part of this
ID: 879045 • Letter: 1
Question
1. What is the purpose of calibrating a pH meter? 2. For the first part of this experiment, a sodium hydroxide solution was created and standardized. If no NaOH was available to create a standardized basic solution, could another base such as potassium hydroxide (KOH) be used instead? What would be the consequences of using a different base? 3. Does it matter how much water was used to dissolve the KHP? Why or why not? a. Does it matter whether the grams of KHP was accurately measured? Why or why not? 4. If you had substituted a Ca(OH)2 solution of the same molarity and titrated the same unknown HCI solution, how would the volume of Ca(OH)2 necessary to reach the equivalence point be different than that of the NaOH solution? HINT: How many OW ions are produced with Ca(OH)2 versus NaOH? 5. How would your results be different if the unknown HCI solution in part 2 was measured with a graduated cylinder instead of a volumetric pipet? 6. For both parts of the experiment, why was it necessary to perform each titration three times? a. Why was it important to continue the titration past the equivalence point? b. Why was it important to control the drops from the buret when using the drop counter? Why would a steady stream cause you to start over? 7. How would your results be different if you placed the unknown HCI solution in the buret and placed the standardized NaOH solution in the beaker? 8. How does the precision required for Part 1 differ from that of Part 2? 9. What are some sources of errors that are associated with both parts of the experiment? How can you prevent these errors?Explanation / Answer
1. To ensure accurate readings. Calibrating the ph scale makes the observer understand easily the nature of the substance ie acidic or basic.
1-6.99=acidic substance
7.0= neutral
7.1-14=basic substance
2. Changing the base will also change the base reading and thus the final value measured of the unknown solution. However, since NaOH and KOH are both string bases, the readings would not change much in this case.
3. KHP is a weak acid. So the volume of water present would change the amount of solubility of it and hence the pH reading.
Different amounts of KHP would give different pH readings
4. We would have needed 1/2 the volume of Ca(OH)2 as it has 2 OH- ions in it as when compared to NaOH with 1
OH- in it for reaching the equivalence point.
5. Graduated cyllinders are less accurate in measuring the volume of liquids then volumetric pipettes and hence we would have observed error in the final value.
6. Running the reaction three times and taking average reduces the error caused during measurement.
a. When contuning the titration past equivalence point ensures we do not have a false end point of masurement.
b. A steady stream would result in a faster end point most propabaly with an error in the volume and the final pH reading. Thus, it is important to control the volume to get an exact measurement for the end point.
7. If reversing the order of titration, with HCl in the burette and NaOH in the beaker, the end point may be different. We may end up adding more HCl to get an end point.
8. The calibration of pH meter is done to get accurate readings. Changing the base would change the reading slightly. Although it still would be a calibration method.
9. Common errors involved are slow addition of volumes to masure the end point. Measuring beyond end point so we don't have a false end poitn reading. Taking accurate masses wherever possible. Measuring volumes with pippettes.
Related Questions
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.