Please provide an explanation with the answer pH VERSUS VOLUME TITRANT ADDED 14

Question

Please provide an explanation with the answer

pH VERSUS VOLUME TITRANT ADDED 14 12 10 R?S T 0.0 20.0 40.0 60O 80,0 100 Velume 0.100 M NaOH Added (mL.) A 50.0 mL sample of an acid, HA, of unknown molarity is titrated, and the pH of the resulting solution is measured with a pH meter and graphed as a function of the volume of 0.100 M NaOH added. 17. A student carries out the same titration but uses an indicator instead of a pH meter. If the indicator changes color slightly past the equivalence point, what will the student obtain for the calculated concentration of the acid? a. b. c. d. slightly less than 0.0800 M slightly more than 0.0800 M slightly less than 0.125 M slightly more than 0.125 M

Explanation / Answer

As per the given graph equivalence point is at 40mL. So using indicator student will obtain reading of NaOH slightly above 40mL. Let us assume 42 mL of NaOH. Then using titration formula,

N1V1 = N2V2....Where N1= concentration of acid, V1 = 50mL, N2=0.100 M , and V2= 42mL

So, N1= (0.1×42) / 50 = 0.084 M

Now, if we calculate same concentration using graph reading V2= 40mL

Then N1= 0.08 M

So, the student will obtain slightly more than 0.0800M concentration of acid.

Thus answer is option b.

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