1.12 Acids and Bases Flashcards
What is Arrhenius’ theory for what acids and bases are?
-Acids are substances that produce hydrogen ions in solution, and Bases are substances that produce hydroxide ions in solution
What is a hydroxonium ion?
Scientists discovered that H+ cannot exist independently in aqueous solution as it has no electrons. Instead, H+ associates with water and forms the hydroxonium ion (H3O+)
What are Brønsted-Lowry’s definitions for what Acids and Bases are?
-An acid is a substance which donates protons in a reaction/ is a proton donor. A base is a substance which accepts protons in a reaction/is a proton acceptor
What are Lewis acids?
Lone pair acceptors
What are Lewis bases?
Lone pair donators
Compare Arrhenius’ and Brønsted-Lowry’s definitions for acids and bases
HCl(aq) + NH3(aq) <=> NH4+(aq) + Cl-(aq)
HCl(g) + NH3(g) <=> NH4+(g) + Cl-(g)
In both these reactions HCl has donated H+ and NH3 has accepted H+. In both the gaseous phase and aqueous solution they are brønsted-Lowry reactions, whereas only the first is an Arrhenius reaction, meaning that the BL theory is more applicable to a wider range of reactions.
What is a conjugate acid?
A conjugate acid is the species produced when a base gains a proton
What is a conjugate base?
A conjugate base is the species produced when an acid loses a proton
Explain what conjugate pairs are (using a reaction as an example)
HA + H20 <=> H3O+ + A-
In the forward reaction, HA is an acid and water a base. However in the backwards reaction the H3O+ is the acid as it donates a proton, and A- the base as it accepts a proton. If you consider HA to be the acid then HA to be the acid then A- is its conjugate base. If you consider A- to be the base then HA is it’s conjugate acid
Give some characteristics of strong acids
Very low pH, and fully ionise/dissociate
Who created the pH scale?
Søren Sørenson
How do you calculate the pH of an acid?
pH = -log10(concentration of H+)
How can you calculate the concentration of H+ using the pH?
10^-pH
What equation can be used to calculate the concentration of H+ after a dilution?
[H+] = ([old H+]xold volume) / new volume
What is Kw?
The ionic product of water
What is the value of Kw at 298K?
1.0x10^-14
How can we calculate the concentration of [H+] in a base?
By dividing Kw by the concentration of [OH-] to give the concentration of [H+]
How can we work out the pH of a mixture of strong bases and strong acids?
1) Calculate the moles of H+ and OH-
2) Excess moles - Limiting moles
3) calculate the concentration from the remaining moles
4) use this concentration to calculate the pH
What is the acid dissociation constant (Ka)?
The quantifiable measurement of the ability of a weak acid to dissociate.
Calculating using the equilibrium HA+H2O<=>A-+H3O+
and the equation Ka= ([H+]x[A-])/[HA]
If a Ka value is high, is the acid stronger or weaker?
Stronger
What are the units for Ka?
Moldm^-3