Buffer pH Change Trick in 60 Seconds! 💡 | NH₃–NH₄Cl Super Shortcut
❓ Question A basic buffer contains: NH 3 = 0.10 mol , NH 4 + = 0.10 mol Strong acid added: HCl = 0.05 mol Given: p K b ( NH 3 ) = 4.745 Find the change in pH after adding HCl. ✍️ Short Solution This is a weak base buffer (NH₃–NH₄Cl). When HCl is added, it reacts completely with NH₃, converting it into NH₄⁺. We then apply the Henderson–Hasselbalch equation for basic buffers to find the new pH. 🔹 Step 1 — Buffer System NH 3 + NH 4 + \text{NH}_3 + \text{NH}_4^+ Both initially = 0.10 mol → Perfect weak base buffer. 🔹 Step 2 — Henderson–Hasselbalch Equation (Basic Buffer) pOH = p K b + log ( salt base ) \text{pOH} = pK_b + \log\left(\frac{\text{salt}}{\text{base}}\right) pH = 14 − pOH \text{pH} = 14 - \text{pOH} Given: p K b = 4.745 🔹 Step 3 — Reaction With Strong Acid HCl reacts fully with NH₃: NH 3 + HCl → NH 4 + \text{NH}_3 + \text{HCl} \rightarrow \text{NH}_4^+ HCl added = 0.05 mol New moles: NH 3 = 0.10 − 0.05 = 0.05 mol \text...