Acid And Bases Flashcards
Brønsted-Lowry acids
Proton donor
Brønsted-Lowry base
Proton acceptor
Conjugate acid base pair
HCl and Cl-
HCl releases a proton to form Cl-
On reverse Cl- reacts with proton to form HCl
Hydronium ion
H3O+
Water accepts proton (base) forming a conjugate acid
Monobasic dibasic & tribasic
Number of hydrogen ions in the acid
Acid +metal
Salt + hydrogen
Acid + carbonate
Salt+ water+ CO2
Acid + base
Salt+ water
pH relationship w [H+]
pH= -log[H+]
H+ = 10-pH
Calculating pH of strong acid
H+ conc= HA conc
pH calculated directly from conc of acid
- log (conc of acid)
Ka
Acid dissociation constant
= [H+][A-]/[HA]
Stronger the acid the larger the Ka value lower the pH
pKa
-logKa
Inverse= 10^-pKa
Stronger the acid the lower the pKa higher the pH
pH of weak acids
Weak acid= equilibrium
Calc conc at equilibriums
Use Ka
H+ = squat root of (Ka x [HA])
-log ans
Approximation using Ka to calculate ph of weak acid
•[H+]=[A-]
Neglects H+ dissociation of water
•[HA eq] = [HA start]neglect decrease in conc
Kw
[H+][OH-]
Ionic product of water
=1 x 10^-14
Buffer
Minimises pH changes when small amounts of acid/ alkali are added
Contain an weak acid and it’s conjugate base
Addition of acid -buffer action
H+ conc increases
React w conjugate base of buffer
Equilibrium shifts to the left removing H+ ions
Addition of alkali - buffer action
OH- conc increases
H+ react forming water
HA dissociates to replenish the H+ ions by shifting equil to the right
Calculating pH of buffer sol
H+= Ka x HA/A
-log ans
Carbonic acid hydrogen carbonate buffer system in the blood
Addition acid react w HCO3- equil shifts to left
Addition alkali OH- reacts w H+ H2CO3 dissociates to replenish H+ ions
pH titration curve
Base added acid in excess once slightly
As vertical section approach pH increase starts to quicken acid used up more
Rapidly increase vertical section
Equivalence point
Centre of the vertical section of the pH titration curve
Volume of solution that exactly reacts with vol of other solution
End point
Weak acid which has a different colour to its conjugate base - end point when in between is formed
Indicator colour changes
OH- react with H+ weak acid colour changes and equil shifts to the right change colour
H+ ions added A - react orange at end point and to red when equil has shifted to the left
Choosing correct indicator
Indicator range must coincide w vertical section of pH titration curve end point and equivalence point coincide
