Half the formic acid solution is neutralised by addition of a KOH solution to it. If Ka (HCOOH)=2*10^-4 the pH of solution is:
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46
Reaction is:
HCOOH + KOH -> HCOOK + H2O
Let initial concentration of HCOOH be c, then after reaction it becomes c/2, and c/2 concentration of HCOOK is also produced. But since HCOO- is conjugate base of HCOOH, a buffer solution is formed. So, we apply the buffer formula;
pH = pKa + log(salt/acid)
= pKa + 0
= -log(2*10^-4)
= 3.7
Here's the derivation of the equation, if you're unaware.
HCOOH + KOH -> HCOOK + H2O
Let initial concentration of HCOOH be c, then after reaction it becomes c/2, and c/2 concentration of HCOOK is also produced. But since HCOO- is conjugate base of HCOOH, a buffer solution is formed. So, we apply the buffer formula;
pH = pKa + log(salt/acid)
= pKa + 0
= -log(2*10^-4)
= 3.7
Here's the derivation of the equation, if you're unaware.
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Divyankasc:
Thanks Flames! :DDDDDD
Welcome :)
I got it to be buffer but got confused about that concentration thing. Ionic
Oh ok. Ionic equilibrium is simple if you just grasp what's going onl
is my weakest chap
Oh xD practice well, it's a semi important chapter in physical Chem.
semi important :OOOOOOOOOOOOOOOOOOOOOOOOOOOO
Thanks
I'll become master of ionic today itself
Goodluck!
Answered by
9
Standard solutions of strong acids and bases are widely used for determinations involving analytes that are acidic or basic or can be made so.
Standard solutions
The standard solutions used in neutralization titrations are strong acids or bases for complete reaction and sharper end points.
Usual acids are HCl, H2SO4 and HClO4 used as cold dilute solutions for safety. HNO3 is too oxidizing and gives unwanted side reactions.
Usual bases are NaOH, KOH and Ba(OH)2.
Acid-base indicators
An acid-base INDICATOR is a weak organic acid or weak organic base that shows a color change between the acid or base and the conjugate form.
If we just consider the acid form, we see from a definition of the dissociation constant Ka, that the color change is determined by the hydronium ion concentration.
The range of the indicator, from what the human eye distinguishes as completely acid to completely base color change, is about
or about a two orders of magnitude change in the indicator concentration ratio from
Look at the table on the inside front cover or table 12-1 (page 268 of Skoog, West, Holler and Crouch) to confirm this observation. Indicators are available for any pH range. The pH of the color change is somewhat dependent upon temperature, the solvent and the presence of colloidal particles.
Example: An acidic indicator with a dissociation constant of 10-5 and exhibiting a color change from pink (acid) to yellow (conjugate base) has a pKa = 5 and therefore will be pink at about pH = 4 and yellow at pH = 6.
Standard solutions
The standard solutions used in neutralization titrations are strong acids or bases for complete reaction and sharper end points.
Usual acids are HCl, H2SO4 and HClO4 used as cold dilute solutions for safety. HNO3 is too oxidizing and gives unwanted side reactions.
Usual bases are NaOH, KOH and Ba(OH)2.
Acid-base indicators
An acid-base INDICATOR is a weak organic acid or weak organic base that shows a color change between the acid or base and the conjugate form.
If we just consider the acid form, we see from a definition of the dissociation constant Ka, that the color change is determined by the hydronium ion concentration.
The range of the indicator, from what the human eye distinguishes as completely acid to completely base color change, is about
or about a two orders of magnitude change in the indicator concentration ratio from
Look at the table on the inside front cover or table 12-1 (page 268 of Skoog, West, Holler and Crouch) to confirm this observation. Indicators are available for any pH range. The pH of the color change is somewhat dependent upon temperature, the solvent and the presence of colloidal particles.
Example: An acidic indicator with a dissociation constant of 10-5 and exhibiting a color change from pink (acid) to yellow (conjugate base) has a pKa = 5 and therefore will be pink at about pH = 4 and yellow at pH = 6.
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