Department of Chemistry and Biochemistry Post Lab Questions Answer the following

Question

Department of Chemistry and Biochemistry Post Lab Questions Answer the following questions in your discussion. 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 OH ions are produced with Ca(OH)2 versus NaoH? 5. How would your results be different if the unknown HCl 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 HCl 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) 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

3) For convenience we disssolve KHP in water in order to do the titration . But the water does not increase or decrease the mass ( or moles) of KHP present. The water itself does not play any role in the reaction. Therefore adding a small or large volume of water to the KHP makes no difference to the titration.

7)

If we initially had HCl in the buret and NaOH in the beaker, we would be titrating a strong base with a strong acid. we would begin with a pH probably around 14 and continuously observe a decline with each addition of HCl, until we reach pH = 7. At this point, the equivalence point, there would be equal moles of HCl as NaOH.

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