A2- Acids and Bases Flashcards
What is a buffer?
a substance that can resist the change in pH when a small amount of acid or alkali is added to it
What is a brønsted-lowry base?
a proton acceptor
What is a brønsted-lowry acid?
proton donor
What is a weak acid?
a proton donor that partially dissociates in water
What is a strong acid?
a proton donor that fully dissociates in water
What is the equation for pH?
pH = -log[H+]
How do you make a buffer?
add sodium salt to weak acid
Why can weak acids only resist the change in pH when H+ is added for a short time?
as less A- initially,
as H+ is added, A- is used up to form HA in a non-reversible reaction
This is quickly used up, and pH will change
Why does adding sodium salts help acids to resist change in pH?
as increases number of A- ions
What makes a suitable indicator?
rapid colour change
How do you calculate the [H+] in sulfuric acid?
2 x [H2SO4]
What assumptions are made when calculating the pH of H2SO4?
- fully dissociated ([H+] = [acid]
- diprotic, so each H2SO4 dissociates into 2 x H+
Why is the pure water always neutral, regardless of pH?
[H+] = [OH-]
Write the equation for the reaction of a strong acid with water
HA + H2O –> H3O+ + A-
Write the equation for the reaction of a weak acid with water
HA + H2O <–> H3O+ + A-
