1. A solution is prepared by adding 100 mL of 0.2 M hydrochloric acid to 100 mL of 0.4 M sodium formate. Is this a buffer solution, and if so, what is its pH?
Sodium formate --> HCOONa
HCOONa -----> HCOO- + Na+
HCOO- + HCl ----------> HCOOH
In another form we can write as
HCOOH --------> HCl + HCOO-
Moles of HCOO- = Molarity*V in L = 100*0.4/1000 = 40 millimoles
Moles of HCl = 0.2*100/1000 = 20 millimoles
HCOOH --------> HCl + HCOO-
0 20 40
20 0 20
pH = pKa + log [HCOONa] / [HCOOH]
Since acidic buffer is formed after adding HCl
we are using the formula
pH = pKa + log [salt] / [Acid]
pH = pKa + log [20 /20]
pH = pKa = 3.75 [since pKa of formic acid is 3.75]
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