Acids, Bases and pH Flashcards
What is the Brønsted-Lowry theory?
A theory that describes acid-base interactions in terms of proton transfer between chemical species
What are Brønsted-Lowry acids?
Proton donors
Why are Brønsted-Lowry acids called proton donors?
They release hydrogen ions when they’re mixed with water
Write the general equation for a general Brønsted-Lowry acid (HA) mixed with water
HA(aq) + H2O(l) ⇌ H3O+(aq) + A-(aq)
What are Brønsted-Lowry bases?
Proton acceptors
Why are Brønsted-Lowry bases called proton acceptors?
When they’re in a solution, they grab hydrogen ions from water molecules
Write the general equation for a general Brønsted-Lowry base (B) in a solution
B(aq) + H2O(l) ⇌ BH+(aq) + OH-(aq)
What do acids and bases do in water?
Break up into positive and negative ions (called dissociation)
What do strong acids do in water?
They dissociate almost completely in water - nearly all H+ ions are released
What do strong bases do in water?
They dissociate almost completely in water
What do weak acids do in water?
They dissociate only partially - so only a small amount of H+ ions are formed
What do weak bases do in water?
They only slightly dissociate
Describe the equilibrium position in the reversible reaction when a strong acid mixes with a water
The equilibrium lies far to the right, which is why nearly all the H+ ions are released
Describe the equilibrium position in the reversible reaction when a weak acid mixes with a water
The equilibrium lies far to the left, which is why only a small amount of the H+ ions are released
What are monobasic acids?
An acid that releases one H+ ion per molecule
What are monobasic acids also called?
Monoprotic acids (because an H+ ion is just a proton)
Give 2 examples of monobasic acids
HCl
HNO3
What are dibasic acids?
An acid that releases two H+ ion per molecule
Give an example of dibasic acids
H2SO4
What are tribasic acids?
An acid that releases three H+ ions per molecule
Give an example of a tribasic acid
H3PO4
What are tribasic and dibasic acids examples of?
Polyprotic acids
What is a species?
A type of chemical - could be a molecule, atom or an ion
What are conjugate pairs?
Species that are linked by the transfer of a proton (H+ ion)
What is the general equation for the equilibrium reaction between an acid and a base? Show the conjugate pairs
HA + B ⇌ BH+ + A-
HA ⇌ A- is conjugate pair 1 (acid1 —> base1)
B ⇌ BH+ is conjugate pair 2 (base2 —> acid2)
In a balanced chemical equation, where will you find conjugate pairs?
On either side of the chemical equation
Describe a conjugate pair and the proton transfer between them
When a conjugate acid loses a proton, it forms a conjugate base. But when this conjugate base gains a proton, it forms a conjugate acid
What is the conjugate acid when water reacts with acids?
H3O+
What is the conjugate base when water reacts with bases?
OH-
What is the general equation for when an acid dissolves in water? State the conjugate pairs
HA + H2O ⇌ H3O+ + A-
HA (acid1) ⇌ A- (base1)
H2O (base2) ⇌ H3O+ (acid2)
What is the general equation for when a base dissolves in water? State the conjugate pairs
B + H2O ⇌ BH+ + OH-
B (base1) ⇌ BH+ (acid1)
H20 (acid2) ⇌ OH- (base2)
How do you identify conjugate pairs?
By looking at the chemical equation for 2 species that are linked by proton transfer
Two species can’t be a conjugate pair if…?
… they are on the same side of the chemical equation
What are the products of the reaction between a reactive metal and acid?
Salt and Hydrogen gas
In the reaction between a metal and an acid, what is oxidised and what is reduced?
The metal atoms donate electrons to the H+ ions in the acid solution. The metal atoms are oxidised and the H+ ions are reduced
What are the products of the reaction between an acid and a carbonate?
Carbon dioxide, water and a salt
What is the product when an acid reacts with a base or an alkali?
Water
What ions are produced in the reaction between an acid and an alkali?
Acids produce H+ ions and the alkalis produce OH- ions when dissolved in water
What is an alkali?
A base that releases OH- ions when they dissolve in water
What type of reaction is Acid + Base?
Neutralisation
What is the ionic equation for the reaction between an acid and an alkali?
H+(aq) + OH-(aq) —> H2O(l)
What is the ionic equation for the reaction between an acid and an insoluble base?
H+(aq) + O2-(s) —> H2O(l)
What is pH?
A measure of the hydrogen ion concentration in a solution
What is the equation for pH?
-log[H+]
What is the range of the pH scale?
0 (very acidic) to 14 (very alkaline)
What is the pH of water?
pH7 (neutral)
For a monobasic acid, how can you work out the concentration of the H+ ion if you know the concertation of the acid?
Each mole of acid produces one mole of hydrogen ions, so the H+ concentration is the same as the acid concentration
What are the products when water dissociates?
Hydroxonium ions and Hydroxide ions
What equilibrium exists in water, then simplify it?
H2O(l) + H2O(l) ⇌ H3O+(aq) + OH-(aq)
remove H2O from both sides:
H2O ⇌ OH-(aq) + H+(aq)
Why does the equilibrium for the dissociation of water lie far to the left?
Because water only dissociates a tiny bit, so most is just H2O
What is the ionic product of water?
An equilibrium constant specific to the dissociation of water at a constant temperature
What is the equation for the ionic product of water?
Kw = [H+][OH-]