Chapter 16
Acid-Base Equilibria
By Boundless
The equilibrium constants for homogeneous and heterogeneous solutions need to be calculated differently.
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The common ion effect describes the changes that occur with the introduction of ions to a solution containing that same ion.
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A buffer is a solution of weak acid and conjugate base or weak base and conjugate acid used to resist pH change with added solute.
![Thumbnail](../../../../../figures.boundless-cdn.com/29982/square/ice table.jpg)
The pH of a buffer solution can be calculated from the equilibrium constant and the initial concentration of the acid.
The Henderson–Hasselbalch equation connects the measurable value of the pH of a solution with the theoretical value pKa.
The changed pH of a buffer solution in response to the addition of an acid or a base can be calculated.
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An alkaline buffer can be made from a mixture of the base and its conjugate acid, but the formulas for determining pH take a different form.
![Thumbnail](../../../../../figures.boundless-cdn.com/13924/square/acetic-acid.jpeg)
The pH of a buffer depends on the ratio [base]/[acid] rather than on the particular concentration of a specific solution.
![Thumbnail](../../../../../figures.boundless-cdn.com/13947/square/hydrochloric-acid-05.jpeg)
For an effective buffer, there must be enough acid/conjugate base to consume all newly added ions so that the pH is maintained.
![Thumbnail](../../../../../figures.boundless-cdn.com/30003/square/titration curve for oxalic acid with naoh showing the buffering region.jpg)
A buffer's capacity is the pH range where it works as an effective buffer, preventing large changes in pH upon addition of an acid or base.
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A strong acid will react with a strong base to form a neutral (pH = 7) solution.
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A weak acid will react with a strong base to form a basic (pH > 7) solution.
![Thumbnail](../../../../../figures.boundless-cdn.com/13925/square/tit1.jpg)
A strong acid will react with a weak base to form an acidic (pH < 7) solution.
![Thumbnail](../../../../../figures.boundless-cdn.com/13988/square/rxn-tri.jpg)
Polyprotic acids, also known as polybasic acids, are able to donate more than one proton per acid molecule.
![Thumbnail](../../../../../figures.boundless-cdn.com/13611/square/indicator-20table.jpg)
An indicator is a weak acid (or a weak base) that has different colors in its dissociated and undissociated states.
![Thumbnail](../../../../../figures.boundless-cdn.com/30030/square/ice table for the ksp of fe(oh)2.jpg)
The solubility product is the equilibrium constant representing the maximum amount of solid that can be dissolved in aqueous solution.
![Thumbnail](../../../../../figures.boundless-cdn.com/10395/square/chromatography-tank.jpg)
Molar solubility is the number of moles of a solute that can be dissolved per liter of solution before the solution becomes saturated.
![Thumbnail](../../../../../figures.boundless-cdn.com/10264/square/precipitation.jpeg)
A set of rules can be used to predict whether a combination of cations and anions in solution will recombine and precipitate.
![Thumbnail](../../../../../figures.boundless-cdn.com/10442/raw/on-structural-formulae-v.1.jpg)
By changing the pH of the solution, you can change the charge state of the solute.
![Thumbnail](../../../../../figures.boundless-cdn.com/10300/square/8050390244-2d2a2eac1d-n.jpeg)
Fractional precipitation can be used to determine which ions are present in a solution by taking advantage of their different solubilities.
![Thumbnail](../../../../../figures.boundless-cdn.com/30993/square/ide-with-carbonate-growths.jpeg)
Adding a common ion decreases the solubility of a solute, causing it to precipitate.