Acids, Bases & Buffers Flashcards
What is the Arrhenius concept?
- Acids are substances that when dissolved in water, increase the H+ concentration
- Bases are substances that when dissolved in water, increase the hydroxide ion concentration
What is the Brønsted Lowry theory?
- An acid is a substance that can donate protons to another substances
- A base is a substance that can accept H+ from another substance
What is the Lewis theory?
- An acid is a substance that can accept electrons from another substance
- A base is a substance that can donate electrons to another substance
What is a monoprotic acid?
An acid that can transfer 1 H+ per molecule during an acid-base reaction
What is a diprotic acid?
An acid that can transfer 2 H+ per molecules during an acid-base reaction
What is a tripotic acid?
An acid that can transfer 3 H+ per molecule during an acid-base reaction
What is the auto-ionisation of water?
The ability of water to act as either a proton acceptor (base) or a proton donor (acid)
In the presence of a base, how does water act?
As an acid
In the presence of acid, how does water act?
As a base
What does Kw mean?
The ionisation constant of water
What is the ionisation constant equation?
Kw = [H3O+] [OH-] = 1.0 x 10 -14
How do you calculate H+ from OH-?
1 x 10 -14
/
Concentration of OH-
PH = -log [ans] =
What is the concentration of H+ in a solution that contains 0.01M OH-?
[H+] = 1 X 10 -14 / .01M = 1 x 10 -12 M
-log10 [1 x 10 -12] = 12
What are conjugate base pairs?
Consists of 2 substances that differ by the presence of a proton
If the acid is strong, is the conjugate base strong or weak?
Weak
If the base is strong, is the conjugate acid strong or weak?
Weak
How do you calculate the pH of a strong acid?
PH. -log10 [H+]
How do you calculate the pH of a strong base?
pOH = -log10 [OH-]
14 - pOH
Which type of acid dissociates fully?
Strong acids
What does Ka mean?
Acid-dissociation constant
The larger the Ka value, the stronger the acid
What is the equation to work out Ka?
[Hydrogen ion] [Conjugate base]
/
[Weak acid]
What does Kb mean?
Base-dissociation constant
How do you calculate the pH of a strong acid?
-log10 (concentration)
How do you calculate the pH of a weak acid?
1. Ka = [H+]²
/
[HA]
2. REARRANGE
Ha (Ka) = H+
3. Square root
4. -Log10 (ans)What is a buffer?
Weak acid-base conjugate pairs
What 2 factors determine pH?
- Value of Ka
- Ratio of conjugate acid base pair concentrations
Why do buffers resist changes in pH?
Because it contains:
- an acidic species to neutralise OH-
- a basic species to neutralise H+
What is the Henderson-Hasselbalch equation?
pH = pKa + log [Base]
/
[Acid]
How is the acid-dissociation constant (Ka) calculated?
[Hydrogen ion] [Conjugate base]
/
[Weak acid]
How is the base-dissociation constant (Ka) calculated?
[Hydroxide ion] [Conjugate acid]
/
[Weak base]
How do you determine pKa?
-log Ka
