Buffer capacity is a measure of a buffer solution\'s resistance to changes in pH

Question

Buffer capacity is a measure of a buffer solution's resistance to changes in pH as strong acid or base is added. An ideal buffer has equal concentrations of acid and conjugate base for a [basel to [acid] ratio of 1. A buffer has lost its capacity when the ratio of [base] to [acid] is less than 0.10 or greater than 10. Suppose that you have 185 mL of a buffer that is 0.200 M in both propanoic acid (C2HsCOOH) and its conjugate base (C2HsCOO). Calculate the maximum volume of 0.450 M HCI that can be added to the buffer before its buffering capacity is lost.

Explanation / Answer

let x= volume of HCl to be added in L, moles of HCl to be added= Molarity* volume in L= 0.45x

moles of propanoic acid = 0.2*185/1000 =0.037 moles= moles of propanoic acid

all the HCl reacts and hence moles of propanoic acid formed= 0.037+0.045x and moles of conjugate base =0.035-0.45x

volume of solution after mixing = 185/1000+x

conocentrations : propanoic acid [HA]= (0.037+0.045x)/(x+0.185) and conjugate base [A-]= (0.037-0.45x)/ (x+0.185)

since buffering capacity is lost when [A-]/[HA] is <0.1 or >10

HCl reacts with the conjugate base and increases [HA], So the ratio decreases. Hence for maximum HCl adddition, the ratio of [A-]/[HA has to be less than 0.1

[A-]/[HA]= 0.1

0.037-0.45x= 0.1*(0.037+0.45x)

0.037*(1-0.1)= 0.45x*1.1

x=0.067L or 0.067*1000= 67 ml of HCl

Related Questions

Navigate

• Browse (All)
• Browse B
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.