three buffers are prepared using equal concentrations of formic acid (HCOOH) and
ID: 556232 • Letter: T
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three buffers are prepared using equal concentrations of formic acid (HCOOH) and sodium formate, hydrofluoric acid (HF), and sodium fluoride, and acetic acid (CH3COOH), and sodium acetate. Rank the three buffers from highest to lowest pH
Edit View History Bookmarks People Window Help orks for Chemistryx Smartwork5 x YM4 - hannahndhouz@gmail.com x 5://ncia.wwnorton.com/18156 Q ks o YouTube D Google Docs M GMAIL NA ILearn RR'Web o Chemistry Book N Netflix D THE CALCULUS P. E 11/11/17 61% 05 Question (1 point) O See page 792 Three buffers are prepared using equal concentrations offormic acid (HCOOH) and sodium formate, hydrofluoric acid (HF) andsodium fluoride, and acetic acid (CH3COOH)and sodium acetate. Rank the three buffers from highest to lowest pH. 1st attempt I See Periodic Table o See Hint According to the text, the Kof the acids are as follows: HCOOH: 1.77104 HE: 6.8*104 CH3COOH: 1.76 x 10-5 Options (3 items) (Drag and drop into the appropriate Options in order Highest pH CH3COOHiciscoona Naf 8 OF 1RCUESTIONS COMPLETE NUOT ANSWER IMG 1882.jpg Canceled 3 jpg a IMG 1882.jpg + sExplanation / Answer
Buffer A formic acid + sodium formate
Buffer B Hydrofluoric acid + sodium fluoride
BufferC acetic acid + sodium acetate
The pH of buffer is calculated by Hendersen equation as
pH = pKa + log [conjugate base]/[acid]
As equal quantities of both salt and acid are added
the pH of buffer = pKa in each case.
Thus the acid with lowest pka has lowest pH , that is hydrofluoric acid(the strongest of three) and
the acid with highest pka is acetic acid (weakest among three) .
pK aof formic acid = 3.74
pKa of hydrofluoric acid = 3.14
pKa of acetic acid = 4.74
Thus highest to lowest ph of buffers is
acetate/acetic acid > formate/formic acid > fluoride / HF
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