Which is the best indicator for the titration of HCI solution with NaOH solution

Question

Which is the best indicator for the titration of HCI solution with NaOH solution? An employer is interviewing four applicants for job a laboratory technician and each now to prepare a buffer solution with a pH close to 9 aerie A. says he would mix acetic acid and sodium acetate solutions. Beula B. says she would mix NH_4CI and HCI solutions Carla C. says she would mix NH.CI and NH, solutions. Dexter D. says he would mix NH, and NaOH solutions. Which of these applicants has given an appropriate procedure? Explain your answer and explain what is wrong with the erroneous procedures. If the concentrations of both the acid and the conjugate base in a given buffer are doublet how would the pH be affected? How would the capacity of the buffer be affected?

Explanation / Answer

Q6.

for HCl and NaOH... the equivalence point will be at pH = 7

so we need anything around 7-8 since very small amount of NaOH will increase the pH rapidly

so:

best option:

c --> from 6.5 to 7.8

and most preferably

d --> colorless ... it appears to be a large change from 7 to 9.9 but in reality this is about a fraciton of mL of base excess...

Q7

for a buffer, we require a strong acid/base an its conjguate base/acid respectively

so:

A is wrong, since conjugate won't match

B is correct, NH4Cl + HCl --> NH3 Cl-, therefore, NH3 and NH4+ are present

C is also correct since bot NH4 and NH3 are present

D is incorrect, since there isno conjugate formation

Bonus:

if you double concentrations, the overall ratio --> conjugate/acid --> 1/1 = 1 and 2/2 = 1 remains the same

so pH remains partially the same

the capacity of buffer is affected, since there is higher concnetration, so it increases

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