Acid - Base equilibria Flashcards
What is a bronsted acid
Proton donor
What is a bronsted base
Proton acceptor
For the reaction NH3 + H2O ⇌ NH4+ + OH- , what are the conjugate acid base pairs?
- NH3 accepts a proton to become NH4+, NH3 acts as a brØnsted Lowry base
- H2O donates a proton, thus acting as a brØnsted Lowry acid
- NH3 and NH4+ are a conjugate acid base pair
- H2O and OH- are a conjugate acid base pair
What is a strong acid
Fully dissociates in solution, can be mono, di or tribasic
What is mono/di basic
monobasic - donates 1 proton per molecule of acid
di - donates 2 protons per molecule of acid
What is a weak acid ?
Partially dissociates in solution
What is the formula for pH?
pH = -log[H+]
What does [H+] equal
[H+] = antilog(-pH)
Draw out the table for converting between [acid] [H+] and pH
on page
What is the ionic product of water?
Kw = [H+][OH-]
units of mol^2dm^-6
At 25ºC , Kw = 1 x10 -14
What is Kw in pure water?
in pure water [H+] = [OH-] therefore Kw = [H+]^2
What is the table for converting between pH of strong alkalis
on page
What are the equations for pKw, pOH,
pKw = -log Kw pKw = 14.00 at 25ºC
pOH = -log[OH-]
pH + pOH = pKw
What is the general acid dissociation for a weak acid?
HA ⇌ H+ + A-
What is Ka
Ka = [H+][A-]
————-
[HA]
Always has units of moldm^-3
What does a higher Ka suggest
A higher Ka suggests a ‘stronger’ weak acid
What is the table for converting between a weak acid and pH?
on page
What happens when an acid or alkali is neutralised or diluted?
The concentration of the ions in solution changes
What is the formula for working out concentration of a diluted solution?
on page
What is the formula for working out The neutralisation
on page
What is a buffer?
A solution that resists small changes in pH on addition of small amounts of acid or alkali
What is the buffering action represented by?
HA ⇌ H+ + A-
What is the buffering action when extra acid is added
- Extra Hydrogen ions are added
- The anion in the buffer reacts with the H+
( H+ + A- →HA ) - The extra H+ ions are removed
- This maintains [H+] and maintains pH
What happens on the addition of alkali
- Extra hydroxide ions are added
- These react with the undissociated acid in the buffer solution (HA + OH- → A- + H2O)
- Extra OH- ions are removed
- This maintains [H+] and maintains pH
What is the henderson-Hasselbalch equation?
on page
Draw out the four different titration curves, state what the reaction is between and suggest a suitable indicator.
in book
What is the pH range for phenolphthalein and what titrations is it suitable for?
8.3 to 10.0
Strong - Strong
Weak - Strong
What is the pH range for methyl orange and what titrations is it suitable for?
3.1 - 4.4
Strong - Strong
Strong - Weak
What is the pH range for methyl red and what titrations is it suitable for?
4.4 - 6.2
Strong - Strong
Strong - Weak
What is salt hydrolysis?
When all or some of the H+ ions in an acid are replaced with positive ions
What are the four things that salts can be made from and what is the solution (acidic or alkaline)
- Strong acid - Strong base e.g. NaCl and solution is neutral
- Strong acid - Weak base e.g. NH4NO3, solution is acidic
- Weak acid - Strong base e.g. CH3COONa, solution is alkaline
- Weak acid - Weak base e.g. CH3COONH4, either acidic or alkaline
For the previous question, for 1, 2 and 3 what happens in water.
- Neither of the ions from the salt react with water
- The positive ion react with water donating a H+ to form the acidic hydronium ion
- The negative ion reacts with water, the water donates a H+ leaving OH- ions in solution
