3.3.12- Acids and Bases (PAPER 1)
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What is a Bronsted- Lowry acid?
A proton donor (H+) When we mix acids with water, H+ ions are released.
Use HA to show how H+ ions are formed.
HA(aq) + H2O(l) —–> H3O+ (aq) + A- (aq)
What is a Bronsted-Lowry base?
A proton acceptor When we mix bases with water, they react with H+ ions to make OH- hydroxide ions.
Use B for base to show how hydroxide ions are formed
B (aq) + H2O (l) ——> OH- (aq) + BH+ (aq)
What is the Bronsted-Lowry acid-base reaction?
A reaction involving the transfer of a proton
What do H+ ions form in water?
Hydroxonium ions H3O+, these ions make a solution acidic.
What is the difference between strong and weak bases?
Strong bases are fully ionised in solution to convert into OH- ions whereas weak bases do not convert fully into OH- ions in solution.
What is the difference between strong and weak acids?
Strong acids dissociate/ ionise completely in aqueous solutions to produce high conc of H+ ions whereas weak acids only partially dissociate to produce low conc of H+ ions.
What are examples of weak acids?
Carboxylic acids such as CH3COOH (ethanoic acid) CH3OOH ⇌ CH3COO- + H+ Backwards reaction is favoured with weak acids so not many H+ ions produced, equilibrium far on the left.
What are examples of strong acids?
HCl- hydrochloric acid H2SO4- sulfuric acid HNO3- nitric acid HCl ⇌ H+ + Cl- Forwards reaction is favoured with strong acids, dissociate almost completely into a large conc of H+ ions, equilibrium on right.
What are examples of strong bases?
NaOH- sodium hydroxide KOH- potassium hydroxide NaOH ⇌ Na+ + Cl- Forwards reaction is favoured with strong bases, large conc of OH- ions produced, equilibrium on right.
What are examples of weak bases?
NH3- ammonia NH3 + H2O ⇌ NH4+ + OH- Backwards reaction favoured with weak bases, low conc of OH- ions produced, equilibrium on left.
What is generic example of acid (HA) donating a proton to a base (B)?
HA (aq) + B (aq) ⇌ BH+ (aq) + A- (aq)
How does water act when an acid is added to it?
As a base- it accepts a proton. HA(aq) + H2O (l) ⇌ H3O+ (aq) + A- (aq)
How does water dissociate?
It dissociates very weakly into OH- and H+ ions. Equation 2H2O ⇌ H3O+ + OH- Simplified equation H2O ⇌ OH- + H+
What would kc equation for water be and why is this inaccurate?
Kc= [H+] [OH-]/ [H2O] The conc of H+/OH- is so little compared to H2O we can assume that conc of H2O has constant value.
What is ionic product of water?
Multiply the 2 previous constants- Kc and H2O to get: Kw= [H+][OH-] units= mol2dm-6
What is the value of Kw at a given temperature?
Kw is the same in a solution at a given temperature: 1.00x10^-14 mol2dm-6 The value changes if temperature changes
What is the conc of H+ and OH- ions in pure water?
They are equal [H+]=[OH-] This can be simplified to: Kw= [H+]^2 in pure water
What is the equation to calculate pH?
pH = −log10 [H+]
Calculate the pH of 0.03moldm-3 HCl
HCl dissociates fully so we assume conc of H+ = conc of HCl pH= -log (0.03) = 1.52
Calculate the concentration of H+ ions of nitric acid with pH 1.7
Inverse the pH equation to give [H+]= 10^-pH [H+]= 10^(-1.7) = 0.020 moldm-3
What are monoprotic acids? Calculating pH of strong acid
These dissociate to produce one H+ ion for every acid molecule Concentration of the acid= concentration of H+ ions Eg HCl or HNO3
What are diprotic acids? Calculating pH of strong acid
These dissociate to produce 2H+ ions for every acid molecule Concentration of acid= 2x concentration of H+ ions Eg H2SO4