C.A. Yates was given a 50.0mL sample of the weak acid. The known concentration o

Question

C.A. Yates was given a 50.0mL sample of the weak acid. The known concentration of the weak acid is .25M. After preparing a buret he delivers 25.0mL of the weak acid into a 100mL Erlenmyer flask. He then titrated this solution using a standardized solution of .15 M NaOH.

a)How many mole of the weak acid were added to the beaker?

b)How many moles of NaOH are required to neutralize (reach the equivalence point) the sample of weak acid)?

c)How many milliliters of the NaOH are required to neutralize sample of the w3eak acid?

d) How many moles of NaOH have been added at one half of the volume in part 'C' (volume at the half, equivalence point)?

e) How many moles of the weak acid have reacted at the half equivalence point?

f) Calculate the pH of the soluation at the half equivalence point.

g) Explain how the pH at the half equivalence point is related to K_a, for the weak acid.

Explanation / Answer

HA + NaOH ------> NaA + H2O

pH = pka + log [NaA]/[HA] is formula ,

at half equivalence NaA moles = HA moles ,hence pH = pka

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