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Unit 17 - Buffers and Titrations - Coggle Diagram
Unit 17 - Buffers and Titrations
17.1 The Common-Ion Effect
common-ion effect
occurs whenever a weak electrolyte (ex. weak acid or base) and a strong electrolyte (salt, strong acid or strong base) contain a common ion
17.2 Buffered Solutions
buffers
solutions that contain a weak acid-base pair and are particularly resistant to pH changes
Buffers resist pH changes because they contain acids to neutralize OH- ions and a base to neutralize H+ ions.
Henderson-Hasselbalch equation
pH = pKa + log([base]/[acid])
Buffer Capacity
the amount of acid or base the buffer can neutralize before the pH begins to rapidly change
pH Range
the pH range over which a buffer acts effectively
When the concentrations of weak acid and conjugate base are equal, pH = pKa
17.3 Acid-Base Titrations
Titrations
a known concentration of base (or acid) (the titrant) is slowly added to a solution of acid (or base) by means of a buret to determine the unknown’s concentration or pH.
A titration curve, a graph of the pH as a function of the volume added titrant can then be produced.
Ideally, the indicator that is used would change color exactly at the equivalence point.
The point where the color of the indicator changes is called the endpoint.
The half-equivalence point (HEP)is the point at which exactly half of the acid in a buffer system has been neutralized.
17.4 Solubility Equilibria
Solubility Product
Ksp
Analyze equilibria reactions that are heterogeneous
The Ksp stays constant despite varying circumstances
Solubility is generally expressed as the mass of solute dissolved in 1L or 100mL
The solubility of a substance can also change as the concentration of other solutes vary
17.5 Factors that Affect Solubility
If one of the ions in a solution equilibrium is already dissolved in a solution, the equilibrium will shift to the left and the solubility of the salt will decrease
If a substance has a basic anion, it will be more soluble in an acidic solution
Anion is a negatively charged ion
If a substance has an acidic anion, it will be more soluble in an basic solution
If a compound contains a basic anion that is the anion of a weak acid, its solubility will increase as the solution becomes more acidic
The solubility of slightly soluble salts containing basic anions increases as [H+] increases and as the pH is lowered
17.6 Precipitation and Separation of Ions
The reaction quotient, Q, can be used to determine the direction a reaction must proceed to reach equilibrium
Relations between Q and Ksp can be used to determine if a precipitate forms
Q = Ksp, the system is at equilibrium
Q < Ksp, more solid can dissolve in the solution
Q > Ksp, salt will precipitate untill the solution Q = Ksp