Identify which salt ion actually transfers a proton
A salt can be acidic, basic or approximately neutral depending on its ions.
Learning outcome: Switch the reactive ion while keeping concentration and parent pK fixed. Derive KaKb=Kw, identify the inert counterion and compare acidic/basic pH around neutrality.
Starting recap
Refresh proton equivalents, conjugate pairs, logarithmic dimensionless activity, analytical amount/volume, mass and charge balances, and bounded observational criteria.
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Try
At Kw10⁻¹⁴, a parent Ka10⁻⁵ has conjugate Kb10⁻⁹. A .0500 M sodium A packet is basic; a BH chloride packet whose parent B has Kb10⁻⁵ is acidic.
Open the experimentPredict
Does electrical neutrality of the whole salt require neutral pH?
Experiment
Switch the reactive ion while keeping concentration and parent pK fixed. Derive KaKb=Kw, identify the inert counterion and compare acidic/basic pH around neutrality.
Track the reactive ion in an acidic or basic salt
Worked teaching model · synthetic values · Fictional .0500 M salt; counterions are explicitly inert and monovalent. Choice0 has conjugate base A− whose parent HA has Ka=10⁻pK; choice1 has conjugate acid BH+ whose parent B has Kb=10⁻pK. Ideal activities, Kw=10⁻¹⁴. Metal-ion Lewis hydrolysis and salts with two reactive ions are discussed but not silently included.
Reset keeps your prediction, captures and practice history.
- Salt pH versus parent pK: solid
Axes rescale. A concentration scan, imposed-pH distribution and titration curve have different horizontal meanings. Read each axis and preserve the difference between an imposed condition and an inferred equilibrium.
All calculated plot coordinates
| parent weak-species pK | pH |
|---|---|
| 4 | 8.349909 |
| 4.02 | 8.359889 |
| 4.04 | 8.369871 |
| 4.06 | 8.379853 |
| 4.08 | 8.389835 |
| 4.1 | 8.399819 |
| 4.12 | 8.409803 |
| 4.14 | 8.419788 |
| 4.16 | 8.429774 |
| 4.18 | 8.43976 |
| 4.2 | 8.449747 |
| 4.22 | 8.459734 |
| 4.24 | 8.469722 |
| 4.26 | 8.47971 |
| 4.28 | 8.489699 |
| 4.3 | 8.499689 |
| 4.32 | 8.509679 |
| 4.34 | 8.519669 |
| 4.36 | 8.52966 |
| 4.38 | 8.539651 |
| 4.4 | 8.549642 |
| 4.42 | 8.559634 |
| 4.44 | 8.569627 |
| 4.46 | 8.579619 |
| 4.48 | 8.589612 |
| 4.5 | 8.599605 |
| 4.52 | 8.609598 |
| 4.54 | 8.619592 |
| 4.56 | 8.629586 |
| 4.58 | 8.63958 |
| 4.6 | 8.649575 |
| 4.62 | 8.659569 |
| 4.64 | 8.669564 |
| 4.66 | 8.679559 |
| 4.68 | 8.689554 |
| 4.7 | 8.69955 |
| 4.72 | 8.709546 |
| 4.74 | 8.719541 |
| 4.76 | 8.729537 |
| 4.78 | 8.739533 |
| 4.8 | 8.749529 |
| 4.82 | 8.759526 |
| 4.84 | 8.769522 |
| 4.86 | 8.779519 |
| 4.88 | 8.789516 |
| 4.9 | 8.799512 |
| 4.92 | 8.809509 |
| 4.94 | 8.819506 |
| 4.96 | 8.829503 |
| 4.98 | 8.8395 |
| 5 | 8.849498 |
| 5.02 | 8.859495 |
| 5.04 | 8.869492 |
| 5.06 | 8.87949 |
| 5.08 | 8.889487 |
| 5.1 | 8.899485 |
| 5.12 | 8.909483 |
| 5.14 | 8.91948 |
| 5.16 | 8.929478 |
| 5.18 | 8.939476 |
| 5.2 | 8.949474 |
| 5.22 | 8.959472 |
| 5.24 | 8.96947 |
| 5.26 | 8.979467 |
| 5.28 | 8.989465 |
| 5.3 | 8.999463 |
| 5.32 | 9.009461 |
| 5.34 | 9.019459 |
| 5.36 | 9.029457 |
| 5.38 | 9.039456 |
| 5.4 | 9.049454 |
| 5.42 | 9.059452 |
| 5.44 | 9.06945 |
| 5.46 | 9.079448 |
| 5.48 | 9.089446 |
| 5.5 | 9.099444 |
| 5.52 | 9.109442 |
| 5.54 | 9.11944 |
| 5.56 | 9.129438 |
| 5.58 | 9.139437 |
| 5.6 | 9.149435 |
| 5.62 | 9.159433 |
| 5.64 | 9.169431 |
| 5.66 | 9.179429 |
| 5.68 | 9.189427 |
| 5.7 | 9.199425 |
| 5.72 | 9.209423 |
| 5.74 | 9.219421 |
| 5.76 | 9.229419 |
| 5.78 | 9.239417 |
| 5.8 | 9.249415 |
| 5.82 | 9.259413 |
| 5.84 | 9.269411 |
| 5.86 | 9.279408 |
| 5.88 | 9.289406 |
| 5.9 | 9.299404 |
| 5.92 | 9.309402 |
| 5.94 | 9.319399 |
| 5.96 | 9.329397 |
| 5.98 | 9.339395 |
| 6 | 9.349392 |
| Quantity | Value | Unit |
|---|---|---|
| Parent ionization constant | 1.000000e-5 | dimensionless |
| Conjugate ionization constant | 1.000000e-9 | dimensionless |
| Product of conjugate constants | 1.000000e-14 | dimensionless |
| Salt pH | 8.849498 | pH units |
| Hydronium concentration | 1.414172e-9 | mol/L |
| Hydroxide concentration | 7.071275e-6 | mol/L |
The conjugate base consumes water protons and makes this salt basic.
KaKb=Kw requires a conjugate pair at the same temperature and compatible activity convention. Neutral-salt reasoning applies only when both ions are effectively inert. A highly charged hydrated metal can acidify by polarizing coordinated water as a Lewis acid; that distinct chemistry and salts with two reactive ions need additional equilibria.
These calculated packets are not performed chemical measurements. Keep feasible inventories, activity conventions, fitting observations and independent checks distinct.
The conjugate base consumes water protons and makes this salt basic.
KaKb=Kw requires a conjugate pair at the same temperature and compatible activity convention. Neutral-salt reasoning applies only when both ions are effectively inert. A highly charged hydrated metal can acidify by polarizing coordinated water as a Lewis acid; that distinct chemistry and salts with two reactive ions need additional equilibria.
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Why do a highly charged hydrated metal ion and a weak conjugate base require different chemical explanations?
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