Chapter 21 - Acids, Bases and Buffers Flashcards
What is the Bronsted-Lowry definition of a base?
A base is defined as a proton acceptor
What is the Bronsted-Lowry definition of an acid?
A acid is defined as a proton donor
What do acid-base reactions therefore involve?
They involve the transfer of protons from the acid to the abse
What is pH and how can it be calculated?
pH is a logarithimic scale which is a representation of the concentration of hydrogen ions in an aqueous solution - the lower the pH the higher the concentration of hydrogen ions present
pH = -log10(H+)
What is true about pure water at room temperature?
It is always pH 7, because a small number of water molecules are dissosciated, forming some H+ ions
What is Kw? What is its equation?
A derivation of the equilibrium constant (Kc), which is the dissosciation constant of water. its equation is:
Kw = [H+][OH-]
Which factor does Kw vary with?
It varies with temperature, because as the temperature increases more water molcules dissosciate, decreasing the pH of the solution
What is a monoprotic acid or base? How does this differ from diprotic ones?
Monoprotic means that in solution it is only capable of donating or accepting one proton (e.g nitric acid or ammonia), whereas diprotic can do two (e.g sulfuric acid), so their concentrations are equal to half of the concentration of the proton concentration (strong acids are said to completely dissosciate)
What is the difference between strong acids and weak acids and strong bases and weak bases?
Strong acids will always completely dissosciate in solution, whereas weak acids will only partially dissociate. The same is true for weak bases versus strong bases, however the inverse is instead true
What is Ka?
The dissociation constant for weak acids
What are the four shapes of the graphs when acids are titrated with bases? (depending on the strength of the acid/base)
Strong acid - weak base - Starts at a very low pH and changes fairly slowly, resulting in a pH a little above 7
Strong acid - strong base - Starts at a very low pH and changes quickly, becoming a very high pH
Weak acid - weak base - Starts at a slightly lowered pH and changes slowly to form a pH slightly above 7
Weak acid - strong base - Starts at a slightly lowered pH and changes quickly to a very high pH
What is a buffered solution?
A buffered solution is a solution which is resistant to changes in pH, and therefore will only change slightly in the presence of more acid or base
How are acidic buffer solutions formed? Is the same method used to form basic buffers?
When a small amount of a strong base is added to a weak acid, because the salt formed provides a store of ions in the case of more OH- or H+ ions added. The same is true for basic buffers (but the reverse is true - weak base + strong acid)
What is the equation used to calculate the pH of a weak acid?
Ka = [A-][H+] / [HA]
