Acids and Bases (Physical) (complete) Flashcards
Define Bronsted-Lowry acid
Define Bronsted-Lowry base
Define the reaction between the two.
- acid: proton donor
- base: proton acceptor
- reaction: reaction involving the transfer of a proton.
Define:
- Monoprotic acid
- Diprotic acid
- Triprotic acid
- mono- acid that releases one H+ ion per molecule.
- do- acid that releases two H+ ions per molecule.
- tri- acid that releases three H+ ions per molecule.
Give the definition of pH.
-log[H+]
(2d.p)
Equation to find the concentration of H+ ions in a solution once another solution is added.
[H+] in original solution x (old volume / new total volume)
Describe where Kw comes from.
What is the usual value for Kw at 298K?
Kw = Kc x [H2O]
- During; H2O —(reversible symbol)-> OH- + H+ reaction there is so much water that [H2O] is seen as a constant value, while [H+] and [H2O] are variables.
- As; Kc = ( [H+] x [OH-] ) / [H2O], therefore; Kc x [H2O] = [H+] x [OH-] and Kw = Kc x [H2O]
- This means; Kw = [H+] x [OH-]
Kw = 1 x 10^-14 mol^2dm^-6
What is the effect of temperature on the pH and neutrality of water in terms of Kw?
H2O —(reversible symbol)-> OH- + H+ (—> exothermic)
- As temperature increases, equilibrium shifts right to endothermic direction to oppose increase.
- Therefore [H+] and [OH-] increase, Kw increases and pH decreases.
- However water still neutral as [H+] = [OH-]
Give the definition of neutral
[H+] = [OH-]
Define monobasic/dibasic
monobasic - an alkali that releases one OH- per molecule
dibasic - an alkali that releases two OH- per molecule
Describe the calculation process for calculating the pH of strong acid-strong base mixtures
- Calculate H+ moles
- Calculate OH- moles
- Calculate which XS
- Calculate XS concentration (if OH- then calculate H+ conc, then…)
- Calculate pH
Give the equation for acid dissociation constant (Ka) and pKa
Ka = ([H+] x [A-]) / [HA]
pKa = -log Ka
What is the difference between strong acids and weak acids?
- In strong acids, all molecules break apart to form ions, while in weak acids only a small fraction of the molecules do.
Give the equation for weak acid approximation.
Ka = [H+]^2 / [HA]
What is key about the reaction between weak acids and strong bases?
- When a weak acids reacts with a strong base, for every mole of OH- added, one mole of HA is used up and one mole of A- is formed.
HA + OH- —> A- + H20 (lots)
What are indicators?
Weak acids where HA and A- are different colours
Name the two most common indicators, the colour of their HA and A- and their pH colour range.
- Methyl Orange - HA = bright red, A- = bright yellow, pH colour range = 3.0 - 4.0
- Phenolphthalein - HA = colourless, A- = bright pink, pH colour range = 8.0 - 10.0
What is the endpoint in a titration?
When the indicator changes colour.
Where is the equivalence point found for:
- Strong acid + Strong alkali = pH 7.00
- Strong acid + Weak alkali = pH < 7.00
- Weak acid + Strong alkali = pH > 7.00
Which Ph curve graph has the small ‘lip’ at the start of the curve?
- Weak acid + (either Strong alkali or Weak alkali)
What is a buffer solution?
A solution that resists change in pH when small amounts of acid alkali or water are added.
What are the ingredients of a basic buffer?
Made from a mixture of weak alkali and one of its salts
or mixing excess weak alkali with a strong acid.
What are the ingredients of an acid buffer?
Made from a mixture of weak acids and one of its salts
or mixing an excess of weak acid with strong alkali.
How does an acidic buffer work when a little H+ is added?
How about OH-?
- The added H+ is removed by a reaction with the acid salt to form slightly more of the weak acid
- The salt concentration falls slightly and the weak acid concentration rises slightly, but as the concentration of the weak acid and salt is much larger than the H+ concentration, the ratio of weak acid conc / salt conc remains roughly the same.
- OH- works the same way just opposite with salt and weak acid.
How does a basic buffer work when a little H+ is added?
What about OH-?
- The added H+ is removed by reaction with OH-, so some of the weak alkali reacts to replace the OH-.
- The weak alkali conc falls slightly and the salt concentration rises slightly but as the weak alkali conc and salt conc is much higher than the OH- conc the ratio of weak alkali conc to salt conc remains roughly constant.
- The OH- added is removed by reaction with the salt to form the weak alkali.
- The falling and rising concs works the same as with the H+ just opposite weak alkali and salt.
