pH Calculations/Acids/Bases Flashcards
Outline the equation for pH
pH=-log10[H+]
Outline the equation for [H+]
[H+]=10^-pH
Define a Strong Acid
Fully dissociates (Ionises) in H2O
Outline the Strong Acids
HCl
HNO3
H2SO4
H3PO4
Define Monoprotic Acids
1 mol of protons per mole of acid
Define Diprotic Acids
2 mol of protons per mole of acid
Define Weak Acids
Partially dissociates (Ionises) in H2O
Outline Weak Acids
All Organic Acids - COOH, HF
Outline the 3 pH calculation steps for Dilutions
- Find [H+] of OG Acid
- [H+] of diluted = OG [H+] X OG volume(cm3)/Diluted volume(cm3)
- Diluted pH=-log[H+] of Diluted
Define Ka
Equilibrium Constant for Acids
Outline the Equation for Ka
E.G: HCl -> H+ + Cl-
Ka= [H+] [Cl-]/[HCl]
When do you use Ka?
Used for weak acids
Outline the equation for pKa
pKa=-log10(Ka)
Outline the equation of Ka in regards of pKa
Ka = 10^-pKa
What happens to pKa when at 1/2 neutralisation
pKa=pH
Outline the feature of H2O
It’s amphoteric (can be acid & base)
Outline the pH of pure H2O at 298K only
pH 7
Outline the Kw equation
Kw(mol2dm6) = [H+] [OH-]
When do you use Kw?
Neutral or strong base solutions
What is the value of Kw when pure H2O is neutral at 298K
Kw= 1x10^-14 mol2dm6
What is the new definition of neutral when H2O is neutral at 298K
[H+] = [OH-]
Therefore
Kw = [H+]^2
What is the definition of a base by Bronsted-Lowry?
A proton acceptor
Define a Strong Base
A base that fully dissociates in H2O
Define a Weak Base
A base that partially dissociates in H2O
Define Monobasic Bases
1 mol of OH- per mole of base
Define Dibasic Bases
2 mol of OH- per mole of base
Outline the steps for finding the pH of a buffer when the weak H+ is in excess
- Find excess moles of Weak H+ by - all OH- moles
- Use Ka=[H+][A-]/[HA] & C = (1000 X n)/new V to find [A-] and [HA] with new moles
- Find [H+] and then -log10[H+]
Outline the steps for finding the pH of a buffer when the base is in excess
- Find excess moles of OH- by - all weak H+ moles
- Use Kw=[H+][OH-] & C = (1000 X n)/new V to find [OH-]
- Find [H+] and then -log10[H+]
How do Acidic buffers minimise the effect of added H+ ions?
Weak acids and salt concentration is high so salt ions react with H+ ions to remove them
