Uupunyt Map Strong base is dissolved in 585 ml of 0.200 M weak acid (K, + 4.25 x

Question

Uupunyt Map Strong base is dissolved in 585 ml of 0.200 M weak acid (K, + 4.25 x 10°) to make a buffer with a pH of 397, Assume that the volume remains constant when the base is added. Ha(aq) + OH- (aq) H,0(1) +a(aq) Calculate the pk, value of the acid and determine the number of moles of acid initially present. Number Number pK,= 017 mol 4,3716 0.117 mol HA When the reaction is complete, what is the concentration ratio of conjugate base to acid? Number 0.396643 How many moles of strong base were initially added? Incorrect. Look in the bottom panel for more specific feedback on how to do this part of the calculation. mol OH O Previous & Give Up & View Solution 3 Try Again O Next Exit Explanation BIO 4340 Lecture 5, ...docx 2 BIO 4340 Lecture 4, ...docx - a BIO 4340 Lecture 3, ...docx BIO 4340 Lectur.

Explanation / Answer

moles of weak acid added= molarity* volume in Liters= 0.2*585/1000 =0.117 mloles

Ka= 4.25*10-5, pKa= -log Ka= 4.37

since pH= pKa+ log [A-]/[HA], Handerson and Hasselbach equation

3.97= 4.37+ log [A-]/[HA]

[A-]/[HA]= 0.398, moles of A- formed will be moles of OH- consumed.

moles of A-/ volume/ Moles of HA/ volume = 0.398, since volume is same, the equation becomes

moles of A-/moles of HA=0.398

as per the reaction, HA+ OH- -- ----->H2O(l)+ A-, moles of A- formed is moles of OH added.

let x= moles of OH added= moles of A- formed

moles of HA then will be 0.117-x

x/(0.117-x)= 0.398

x= 0.398*(0.117-x)

1.398x= 0.398*0.117

x= 0.033 moles, moles of OH- added =0.033

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