t- il calculator eal Periodic Table Gradebook Question 4 of 10 Sapling Learning

Question

t- il calculator eal Periodic Table Gradebook Question 4 of 10 Sapling Learning Map . : Strong base is dissolved in 635 mL of 0.200 M weak acid (Ka-417x100) to make a buffer with a pH of 4.17. Assume that the volume remains constant when the base is added. Calculate the pK, value of the acid and determine the number of moles of acid initially present Number Number pK, mol HA When the reaction is complete, what is the concentration ratio of conjugate base to acid? Number ?? How many moles of strong base were initially added? Number mol OH Previous Give Up&View; Solution Check Answer NextExt Hint

Explanation / Answer

weak acid = 635ml of 0.200M

number of moles of weak acid= 0.200Mx0.635L= 0.127 moles

Number of moles weak acid Initially = 0.127 moles

Ka= 4.17x10^-5

-lof(ka) = -log(4.17x10^-5)

PKa= 4.38

PH=4.17

PH= PKa+log[A-]/[HA]

4.17= 4.38 + log[A-]/[HA]

log[A-]/[HA] = -0.21

[A-]/[HA] = 10^-0.21

[A-]/[HA] = 0.616

[A-]/[HA] = 0.616/1.0= 0.616;1

let be the number of moles of base= n moles

4.17 = 4.38 + log(n/0.127)

log(n/0.127) = -0.21

n/0.127= 10^-0.21

n/0.127 = 0.616

n = 0.0782 moles

number of moles strong base= 0.0782 moles.

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