Question

8.Develop a method of titrating your unknowns using a pH meter. 9.Develop a method of titrating your unknowns using an indicator. Discuss how the titration curves generated in the first method will help with the development of this second method. 10.Using the identity and calculated concentration of each unknown sample, calculate the expected initial pH of each unknown.

Answer 1

When a titration is done using pH meter then titration is known as pH metric titrations . In this a pH meter is used to measure the pH of solution every time small amount of base or titrant is added and then a graph is plotted between pH and volume of alkali or titrant added . 'So these are the most important method employed for determining concentration since it does not involve any kind of use of colored indicator and also gives exact values by pH meter which is recorded digitally .

IF we take example of titration of strong base versus strong acid , initially our flask has no base added so pH is noted and then small amount of base is added , so some amount of H⁺ ion present are neutralised by OH^- ions so now pH of solution will rise that is from acidic range it will move towards basic range .

if base is added continuously added , a point will be reached when all of the acid present will be neutralised by base and it will form H₂O and thus pH of solution will sharlpy reaches to or near to 7 and then after this base is added , then pH of solution will increase sharply due to presence of only OH^- ions that are present in solution and at a time pH will become constant due to same OH^- ions present in solution .

So graph is obtained in this and from graph we observe equivalence point

from equivalence point we note volume of base required to neutralise acid

after that by using Molarity or Normality equation , we can find out concentration of unknown sample provided .

graph for strong acid vs strong base is provided below in which equivalence point usually comes at pH 7 only

After equivalence point 77.-- - 7 + Equivalence point ] Before equivaleny point Acid not fully neutralisen Yol of base added