This problem involves perchloric acid (HCIO_4), formic acid (HCOOH), sodium form
ID: 494059 • Letter: T
Question
This problem involves perchloric acid (HCIO_4), formic acid (HCOOH), sodium formate (NaHCOO), and sodium hydroxide (NaOH). What type of acid is HCLO_4 ? [strong or weak ?] Calculate the pH of a solution of 0.327 M HCLO_4. What type of acid is HCOOH ? [strong or weak ?] Calculate the pH of a solution of 0.327 M HCOOH. Which has a lower pH, 0.327M HCLO_4 or 0.327M HCOOH ? Which has a lower [H^+], 0.327M HCLO_4 or 0.327M HCOOH? Calculate the pH of a solution of a solution that is 0.327M HCOOH and 0.327M NaHCOO. What type of base is NaHCOO ? [weak or strong ?] Calculate the pH of a solution of 0.327 M NaHCOO. What type of base is NaOH ? [weak or strong ?] Calculate the pH of a solution of 0.327M NaOH.Explanation / Answer
a) HClO4 is a strong acid thus [acid] = [H+] = 0.327 M
pH = - log (0.327)
= 0.4854
b) HCOOH is week acid with pKa = 3.74 and Ka = 1.8 x 10-4
the pH of weak acid is geiven by
pH = 1/2 pka - 1/2 log C
= (3.74/2 ) - 1/2 log 0.327
= 2.1127
c)HCLO4 being strong acid has lower pH than HCOOH
d) The [H+ ] of HCOOH is less than HClO4
e) A solution containing 0.327M HCOOH and0.327M HCOONa
The solution is a buffer .
the pH of a buffer is calculated using Hendersen equation. pH = pKa + log [conjugate base]/[acid]
HCOOH --------------------> HCOO- + H+
0.327 0.327 x
Ka = x (0.327)/(0.327)
= x =[H+]
thus pH = pKa = 3.74
f) NaHCOO is the conjugate base of a weak acid, so it is strong
It is a salt of weak acid and strong base, hence its pH > 7
pH of the salt is given by
pH = 1/2[ pkw +pka +logC]
= 1/2 [14 +3.74 + log 0.327]
= 8.6272
g)NaOH is a strong base.
For strong base , NaOH , [base] = [OH-] =0.327M
Thus pH = 14 -pOH
= 14 -[-log [OH-]}
= 13.5146
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