patino_chm2046_chapter16

# Base take acid base ph pka log to remove ve sign conj

This preview shows page 1. Sign up to view the full content.

This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: tion: equation: 1 [Acid] pH = pKa - log [Conj. base] take [acid] [base] pH = pKa + log to remove − ve sign [Conj. base] [Acid] The pH is determined largely by the pKa of the The pK acid and then adjusted by the ratio of acid and acid conjugate base. conjugate pH of Buffer (Ka) Q: What is the pH of a buffer that has [HOAc] = 0.700 Q: M and [OAc-] = 0.600 M? and 0.600 HOAc + H2O ⇄ OAc- + H3O+ HOAc + -5 -5 [H3O ] = 2.1 × 10 and pH = 4.67 2.1 pH K = 1.8 × 10 a [Conj. base] pH = pKa + log [Acid] 0.600 pH = − log (1.8 × 10 ) + log 0.700 −5 pH = 4.74 − 0.067 = 4.67 What is the pH of a buffer that is 0.50 M NH3 (pKb = 4.75) and 0.20 M NH4Cl? find the pKb if given Kb Assume the [B] and [HB+] equilibrium concentrations are the same as the initial Substitute into the HendersonHasselbalch Equation Base Form, find pOH Check the “x is small” approximation Calculate pH from pOH NH3 + H2O ⇄ NH4+ + OH− [HB+ ] pOH = pK b + log [B] ( 0.20 ) pOH = 4.75 + log = 4.35 ( 0.50 ) [OH − ] = 10 -pOH = 10 -4.35 = 4.47 × 10 −5 4.47 × 10 −5 × 100% = 0.0089% < 5% 0.50 pH + pOH = 14.00 pH = 14.00 - 4.35 = 9.65 16 pH from using Kb pH Q: What is the pH of a buffer that has What 0.12 mol of NH 3 and 0.095 mol NH4Cl. Kb = 1.8 × 10-5 0.095 Cl. Equilibrium: NH3 + H2O ⇄ NH4+ + OH− Equilibrium: Solution Solution [acid] pOH = pKb + log [base] 0.095 pOH = 4.74 + log 0.12 pOH = 4.74 +( - 0.10) pOH = 4.64 pH = 14.00 – 4.64 = 9.36 The fundamental equations of buffers The If you have a buffer made of a weak acid, HA, and a salt If containing its conjugate base, A−, such as KA (K+ = containing potassium ion), I recommend you to work with the following equilibrium: following HA + H2O ⇄ H3O+ + A− Ka, K of acid HA. HA Any of the four, [HA], [H3O+], [A−], or Ka may be unknown, whereas the others are given. If you have a buffer made of a weak, B, and a salt If containing its conjugate acid, BH+, such as BHCl (Cl− = containing chloride ion. B is not boron element), I recommend...
View Full Document

{[ snackBarMessage ]}

Ask a homework question - tutors are online