Question

For 450.0 ml of a buffer solution that is 0.145 m in ch3ch2nh2 and 8.50×10−2 m in ch3ch2nh3cl , calculate the initial ph and the final ph after adding 1.4×10−2 mol of hcl . ( kb(ch3ch2nh2)=5.6×10−4 .)

Answer 1

The student's question involves the calculation of the initial and final pH of a buffer solution using the Henderson-Hasselbalch equation, involving the knowledge of acid-base chemistry.

Step-by-step explanation:

The student is asking about the calculation of the initial and final pH of a buffer solution consisting of ethylamine (CH₃CH₂NH₂) and its conjugate acid (CH₃CH₂NH₃Cl) before and after the addition of HCl. The Henderson-Hasselbalch equation will be utilized for this calculation.

Calculating Initial pH:

Using the Henderson-Hasselbalch equation for the buffer solution:
pH = pKa + log([base]/[acid])
First, calculate pKa from the given Kb using the relationship pKa + pKb = pKw = 14. Then plug in the concentrations of the base (0.145 M) and acid (8.50×10⁻² M).

Calculating Final pH After Adding HCl:

After adding 1.4×10⁻² mol HCl to the buffer, calculate the new concentrations of base and acid. The moles of CH₃CH₂NH₃Cl will increase while the moles of CH₃CH₂NH₂ will decrease by the same amount. The new concentrations are then used to calculate the new pH using the Henderson-Hasselbalch equation.