Problem: A student dissolves 0.0100 mole of an unknown weak base in 100.0 mL water and titrates the solution with 0.100 M HNO3. After 40.0 mL of 0.100 M HNO 3 was added, the pH of the resulting solution was 8.00. Calculate the Kb value for the weak base.

🤓 Based on our data, we think this question is relevant for Professor Billman's class at Abilene Christian University.

FREE Expert Solution

Recall:

Kb=productsreactants


We shall construct an ICF Chart first:

moles HNO3=40 mL HNO3(10-3 L1 mL)(0.100 mol HNO31 L HNO3)=0.004 moles

We shall construct an ICE Chart based on the following reactions with water:

HB+ + H2O ⇌ B + H3O+

pOH=14-pH

pOH=14-8=6.00

[OH-]=10-pOH

[OH-]=10-6

Calculate the concentrations:

Total volume = 100 mL WB + 40 mL HNO3 = 140 mL

Molarity (M)=moles solute (mol)liter solution (L)

[HB+]=0.004 mol140 mL(10-3 L1 mL)=0.0286 M

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Problem Details

A student dissolves 0.0100 mole of an unknown weak base in 100.0 mL water and titrates the solution with 0.100 M HNO3. After 40.0 mL of 0.100 M HNO 3 was added, the pH of the resulting solution was 8.00. Calculate the Kb value for the weak base.