I need d and e An approximately 0.1-molar solution of NaOH is so be standardized

Question

I need d and e An approximately 0.1-molar solution of NaOH is so be standardized by Assume that the following materials. Clean, dry 50 mL 250 mL Erlenmeyer flask Was bottle filled with distilled water Analytical balance pure solid Morrison acid (to be used as the primary standard) (a) Briefly describe the step a you would take, using the materials listed above, to standardize the NaOH solution. (b) Describe (i.e., set up) the calculations necessary to determine the concentration of the NaOH solution. (c) After the NaOH solution has been standardized, it is used to titrate a weak monotonic acid, HX. The equivalence point is reached when 25.0 mL of NaOH solution has been added. In the space provided at the right, sketch the titration curve, showing the pH changes that occur as the volume of NaOH solution added increases from 0 to 35.0 mL. Clearly label the equivalence point on the curve. (d) Describe how the value of acid-dissociation constant, K_a, for the weak acid HX could be determined from the titration curve in part (c). (e) The graph below shows the results obtained by titrating a different weak acid, H_2Y, with the standardized NaOH solution. Identify the negative ion that is present in the highest concentration at the point in the titration represented by letter A on the curve.

Explanation / Answer

D)

Since this is a weak acid, then there will be buffer formation

if this is true, then

pH =pKa + log(conjugate base / weak acid)

and, in the half equivalence point, we know that

(conjugate base = weak acid)

meaning that

log((conjugate base / weak acid)) = log(1) = 0

so

pH = pKa

the volume of equivalence --> V= 25 mL approx

so half equivalence point --> 25/2 12.5 mL --> the pH at this point -->5.5 approx,

then

pH = pKa = 5.5

e)

H2Y . identify the NEGATIVE ion present in the highest concnetation at the point of "A"

nte that

A is the 2nd ionization of acid

H2Y + OH- --> H2O + HY-

HY- + OH --> Y-2 + H2O

so, the most is Y-2, i.e. the "negative" ion present in A

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