20 Acids, Bases, and pH Flashcards
What is an acid, according to Brønsted-Lowry? (1 mark)
An acids is a proton donor.
What is a base, according to Brønsted-Lowry? (1 mark)
A base is a proton acceptor.
What is a conjugate acid-pair, give an example? (2 marks)
A conjugate acid-pair is two species that can be interconverted by transfer of a proton (H+ ion).
What is a monobasic acid, give an example? (2 marks)
An acid which can donate one proton.
HCl, CH3COOH, HNO3
What is a dibasic acid, give an example? (2 marks)
An acid which can donate 2 protons.
H2SO4, H2CO3
What is a tribasic acid, give an example? (2 marks)
An acid which can donate 3 protons.
H3BO3, H3PO4
What are two ways a neutralisation equation can be written? (2 marks)
H3O+ + OH- —> 2H2O
and
H+ + OH- —> H2O
Who came up with the pH scale? (1 mark)
Søren Sørensen
What is the pH scale? (1 mark)
Numerical scale for measuring hydrogen ion concentrations.
What are the pH values of acidic, alkaline, and neutral solutions? (3 marks)
<7 is acidic
7< is alkaline
=7 is neutral
What is the equation that represents the relationship between pH and the concentration of H+ ions? (2 marks)
pH= -log[H+ (aq)]
or 10^-pH = [H+ (aq)]
What is the concentration of H+ ions in a strong acid with one hydrogen, and why? (2 marks)
The same as the concentration of the acid, because the acid completely disassociates.
Dilution changes the pH of a solution, true or false? (1 mark)
True
What is a chemical called when it can act as an acid or a base? (1 mark)
Amphoteric
Does water act as an acid or base when reacting with strong acids? (1 mark)
Base
Does water act as an acid or base when reacting with weak acids? (1 mark)
Acid
What conjugate base does water form when reacting with strong acids? (1 mark)
H3O+
What conjugate acid does water form when reacting with strong acids? (1 mark)
OH-
What is the dissociation of a strong acid commonly simplified to? (1 mark)
HA(aq) —> H+ (aq) + A- (aq)
What is the concentration of H+ ions in a strong acid with two hydrogen, and why? (2 marks)
Twice the concentration of the acid, because two H+ ions fully dissociate form each molecule.
What is a strong acid, regarding dissociation? (1 mark)
A strong acid completely dissociates in aqueous solution.
What is a weak acid, regarding dissociation? (1 mark)
A weak acid partially dissociates in aqueous solution.
What is Ka? (1 mark)
The acid dissociation constant.
What condition changes Ka? (1 mark)
Temperature
What does a large value of Ka indicate? (1 mark)
That the equilibrium is to the right (towards the products).
What temperature are values of Ka usually standardised at? (1 mark)
25 degrees
What is the general formula for Ka? (2 marks)
Ka= ([H+ (aq)][A- (aq)]) / [HA (aq)]
What does a larger value of Ka indicate, regarding dissociation, why? (1 mark)
Greater dissociation, because the concentration if H+ ions are on top.
What equation links Ka and pKa? (1 mark)
pKa = -log(Ka)
What does a high value of pKa indicate? (1 mark)
The higher it is, the weaker the acid.
What two things does [H+] rely on? (2 marks)
[HA]- concentration of the acid
Ka- the acid dissociation constant
What two approximations are used when calculating the Ka of weak acids? (4 marks)
- That [H+]eqm = [A-]eqm
because HA dissociates equally. - That [HA]eqm = [HA]start
because the dissociation of the weak acids is small you can neglect the increase from start to equilibrium.
Using the two approximations, what can the expression for Ka be simplified to for weak acids? (2 marks)
Ka= [H+]^2/ [HA]
In weak acids, what is wrong with the approximation that states that [H+]=[A-]? (3 marks)
It assumes that the dissociation of water is negligible.
This approximation does not work for very weak acids or very dilute solutions (as HA does not dissociate as much or there is more water to dissociate).
In weak acids, what is wrong with the approximation that states that:
[HA]eqm = [HA]start ? (3 marks)
It assumes that the concentration of the acid is much greater than [H+] at equilibrium.
This approximation does not work for stronger acids or for very dilute solutions.
What is a strong base? (1 mark)
An alkali that completely dissociates in solution.
What is the concentration of water? (1 mark)
55.6moldm-3
How do you calculate the concentration of water? (3 marks)
For 1 dm3 of water, the mass is 1000g (since 1cm3=1g of water).
Using moles= mass/Mr
1000/18= 55.6 moles
Using concentration= moles/volume
55.6 moles/ 1dm3 = 55.6 moldm-3
What is Kw? (1 mark)
The ionic product of water.
What is the equation for the ionic product of water in any aqueous solution? (1 mark)
Kw= [H+(aq)] x [OH-(aq)]
What does Kw vary with? (1 mark)
Temperature
What is the value of Kw at 25 degrees? (1 mark)
1.00 x 10^-14 mol2dm-6
