Acids and bases Flashcards
Bronsted- Lowry acids are?
proton donors
Bronsted-Lowry bases are?
proton acceptors
Describe how acids are proton donors
dissociation is required for a proton to be transferred from an acid to a base- this requires water. Water behaves as a base and accepts a proton forming H3O+(aq)
Describe H3O+(aq)
-conjugate acid
-active acid ingredient, ions make solution acidic
-simple version is H+
Bronsted-Lowry bases are?
proton acceptors
Describe strong and weak bases?
-strong bases dissociate (ionise) almost completely
-weak bases dissociate poorly
Describe strong and weak acids?
-strong acids dissociate (ionise) almost completely
-weak acids dissociate poorly
Describe strong and weak acids?
-strong acids dissociate (ionise) almost completely
-weak acids dissociate poorly
Describe weak acids and provide examples?
-backwards reaction favoured so not many H+ produced
-e.g carboxylic acids
Describe strong acids and provide examples?
-forwards reaction favoured strongly. Lots of H+ produced.
-e.g HCl, H2SO4, HNO3
Describe strong bases and provide examples?
-forward reaction favoured strongly. Lots of OH- ions produced.
-e.g NaOH and KOH
Describe weak bases and provide examples?
-backwards reaction favoured so not many OH- ions produced
-e.g NH3
Acid dissociation equation?
HA(aq) (acid) + H2O(l) (reversible arrow) H3O+(aq) + A-(aq)
Base dissociation equation?
B(aq) (base) + H2O(l) (reversible arrow) BH+(aq) + OH-(aq)
Water dissociation equation?
2 H2O (reversible arrow) H3O+ + OH-
simpler version: H2O (reversible arrow) H+ + OH-
Describe the dissociation of water?
water dissociates into its ions very weakly. There is so little OH- and H+ ions compared to H2O molecules that we assume the concentration of water has a constant value
what are polyprotic/ polybasic acids?
acids which can donate more than one proton
Describe monoprotic/ monobasic acids? provide example
e.g HNO3
1 mole of HNO3 will produce 1 mole of H+ ions
Describe diprotic/ dibasic acids? provide example
e.g H2SO4
1 mole of H2SO4 will produce 2 moles of H+ ions
Describe triprotic/ tribasic acids? provide example
e.g H3PO4
1 mole of H3PO4 will produce 3 moles of H+ ions
Describe how ammonia acts as a base?
-Ammonia doesn’t produce OH- ions directly. It reacts with water first and accepts a proton to produce ammonium ions (NH4+) and OH- ions
-ammonia reacts with acids to make ammonium salts but no water
Equation showing ammonia acting as a base?
NH3(aq) + H2O(l) (reversible arrow) NH4+(aq) +OH-(aq)
Acid + alkali ->
salt + water
Metal + Acid ->
salt + hydrogen
metal oxide + acid ->
salt + water
metal hydroxide + acid ->
salt + water
metal carbonate + acid ->
salt + carbon dioxide + water
what are the rules when writing an ionic equation?
1) write balanced equation
2)add state symbols
3)separate aqueous into ions
4)cancel out spectator ions
can state are metal oxide in?
solid
How are conjugate pairs linked?
they are linked by transferring of a proton
what is a conjugate acid?
a species that has gained a proton
what is a conjugate base?
a species that has lost a proton
equation for reaction between Bronsted-Lowry acids and bases? and describe
HA (acid) + B (reversible arrow) BH+(acid) + A-(base)
- HA is an acid in the forward reaction as it donates a proton
- A- is a base in the reverse direction as it accepts a proton from BH+ to form HA
What are the conjugate pairs in the equilibrium reaction between Bronsted-Lowry acids and bases?
conjugate pair: HA (conjugate acid) and A- (conjugate base)
conjugate pair: BH+ (conjugate acid) and B (conjugate base)
What are the conjugate pairs in the equilibrium reaction between Bronsted-Lowry acids and bases?
conjugate pair: HA (conjugate acid) and A- (conjugate base)
conjugate pair: BH+ (conjugate acid) and B (conjugate base)
what is Kw and its units?
Kw is the ionic product of water
units: mol2dm-6
what is the Kw expression?
Kw= [H+][OH-]
Describe the ionic product of water, Kw?
-the value of Kw is the same (1.00 times 10 to the power of -14 mol2dm-6) in a solution at a given temperature (25 degrees)
-this value changes if the temperature changes
-pure water has an equal concentration of H+ and OH- ions. In other words [H+] = [OH-] therefore when referring to pure water, we can simplify to Kw= [H+]squared
what is pH?
logarithmic scale that measures the concentration of H+ ions in solution
what is the mathematical relationship between pH and the concentration of H+(aq)?
pH= -log[H+(aq)]
what is the equation to determine the concentration go H+ ions?
[H+(aq)] = 10 to the power of -pH
How do you calculate the pH of strong monoprotic acids? (e.g HCl and HNO3)
monoprotic acids dissociate to produce one H+ ion for every acid molecule. This means the concentration of the acid= the concentration of the H+ ions.
How do you calculate the pH of strong diprotic acids? (e.g H2SO4)
Diprotic acids dissociate to produce two H+ ions for every acid molecule. This means that the concentration of the acid= 2 x the concentration of the H+ ions
How do you calculate the pH of strong bases?
-most strong bases dissociate to produce one OH- ion for every base molecule. This means the concentration of the base= the concentration of the OH- ions.
-to work out [H+], use the Kw expression, Kw= [H+][OH-]
What assumptions are made when applying the acid dissociation constant, Ka?
-assumption 1- only a small amount of the weak acid (HA) dissociates so we can assume that- [HA(aq)]equilibrium=[HA(aq)]start
-assumption 2- the dissociation of acid is greater than the dissociation of water present in the solution. We can assume all the H+ ions come from the acid. [H+(aq)]=[A-(aq)] therefore Ka= [H+]squared/ [HA]
What is Ka?
acid dissociation constant.
Where HA(aq) (reversible arrow) H+(aq) + Cl-(aq)
Ka= [H+][A-]/ [HA] units: moldm-3
What is the problem with using Ka values?
it is difficult to compare numbers with negative indices. This problem is solved by converting Ka value into a negative logarithm called pKa.
Describe pKa?
another way of measuring the strength of an acid similar to pH. The lower the value, the stronger the acid.
pKa equation?
pKa= -logKa
inverse : Ka=10 to the power -pKa
How do you measure pH experimentally?
-pH meters are used to measure pH however they must be calibrated correctly
-pH probe must be placed in distilled water first. The meter should be reading pH 7, adjust if not.
-repeat this process with standard solutions at pH 4 and pH 7. Rinse with distilled water between each pH solution.
-wash probe with distilled water after each test
what is a conjugate base pair?
two species differing by H+
what is the Kw value?
1 times 10 to the power of -14
