4.3 Acids and Bases Flashcards
What is a hydrogen ion identical to?
H+ is identical to a proton
What is the Bronsted-Lowry definition of an acid?
A proton donor
What is the Bronsted-Lowry definition of a base?
A proton acceptor
What does “amphoteric” mean?
Can act as both an acid and a base
According to the Bronsted-Lowry theory, when is an acidic substance an acid?
When a base is present
What is an example of an amphoteric substance?
Water
What is a conjugate acid formed from?
Formed from the ions of the base
What pH numbers do acidic solutions have?
Less than 7 at 25C
What is the pH of a neutral solution?
7 at 25C
What pH numbers do basic solutions have?
Greater than 7 at 25C
What is the equation for pH?
pH = -log[H+]
What is the equation for [H+]?
[H+] = 10^(-pH)
What is a strong acid?
A strong acid is fully dissociated in solution
Why is HCl said to be monoprotic?
Because each molecule can donate just one proton
Why is H2SO4 said to be diprotic?
Because each molecule can donate two protons
What is the hydrogen ion concentration in 2.0M sulphuric acid?
4.0M
What is a strong base?
A strong base is fully dissociated in solution
What is the equation for Kw?
Kw = [H+][OH-]
What is the value of Kw at 25C?
1 x 10^(-14)
How can Kw be rewritten for pure water?
Kw = [H+]^2
How can Kw be rearranged to find [H+] of pure water?
[H+] = √(Kw)
What happens to the value of Kw as temperature increases? Why?
Kw increases as temperature increases due to the dissociation of water being endothermic
What are weak acids and bases?
Weak acids and bases are partially dissociated in aqueous solution
What is Ka?
Ka is the acid dissociation constant
What is the equation for Ka?
Ka = ([H+][A-]) / ([HA])
What is the equation for pKa?
pKa = -log(Ka)
Why must Ka be taken into account when working out the pH of weak acids?
Because you cannot assume that the hydrogen ion concentration is the same as the acid concentration, due to it not dissociating fully
How can Ka be rewritten for a weak acid?
Ka = [H+]^2 / [HA]
How can Ka of a weak acid be rewritten to find [H+]?
[H+] = √(Ka X [HA])
What are acid-base titrations used to find out?
They are used to find out the volumes needed to create a neutral solution
What is a pH curve?
The graph of pH against volume of acid or base to create a neutral solution
When does the equivalence point occur when the titration involves monoprotic acids and bases?
When there are equimolar amounts of acid and base present
Where is the equivalence point with a strong acid into a strong base?
pH 7.0
Where is the equivalence point with a strong acid into a weak base?
Below pH 7.0
Where is the equivalence point with a weak acid into strong base?
Above pH 7.0
Where is the equivalence point with a weak acid into weak base?
pH 7.0
What are acid-base indicators?
Acid-base indicators are weak organic acids or bases
Why is universal indicator unsuitable for use in titrations?
It is a mixture of four different indicators, giving it a range of different colours
What is the general equation for an indicator?
HIn (aq) H+ (aq) + In- (aq)
Only when will an indicator be effective in a particular indicator?
When its pH range matches the change in pH at equivalence
What is the definition of a buffer?
A solution which resists small changes in pH when small amounts of acid or base are added to it, or when it is diluted
What are some applications of buffers?
- to calibrate pH meters
- to stop enzymes denaturing after being extracted
- to achieve the correct conditions for dying fabrics
- in shampoo to make the hair look smooth and shiny
What does an acidic buffer contain?
A weak acid and its conjugate base
What does a basic buffer contain?
A weak base and its conjugate acid
What is the equation for working out the [H+] of a buffer?
[H+] + Ka x ([HA] / [A-])
