What is a Bronsted Acid ?
An acid is a proton (ie. H+) donor
HA + H2O ⇔ ? + ?
H3O+ + A-
What is the equation for the equilibrium constant Ka ?
Name the two catergories of Acids in general chemistry ?
- Binary Acids
- Oxy Acids
Describe binary acids ?
Acids composed of hydrogen and a non-metal e.g. HCl
Describe the trend displayed by halogen containing binary acids ?
As halogen size increases, acid strength also increases.
Bond length also increases, which means bond strength decreases, leading to increased acidity.
What are Oxyacids ?
Anions containing a non-metal oxygen such as hydroxide or nitrate ions. They contain:
H - O - X
Describe the acidity of Oxyacids ?
The more oxygen atoms bound to the central atom, the more acidic the oxyacid.
What are diprotic acids ?
Acids with two protons e.g. H2SO4.
Describe the equilibrium constant Ka for diprotic or polyprotic acids ?
The acids would have Ka values for each of its protons, e.g. Ka1 for the first, Ka2 for the second.
The acids ionise in successive steps with their own Ka's.
Ka1 is typically > Ka2
Give 8 examples of strong acids
- Perchloric HClO4
- Chloric HClO3
- Nitric HNO3
- Hydrochloric HCl
- Sulfuric H2SO4
- Hydrobromic HBr
- Hydroiodic HI
- Hydronium ion H3O+
What is a base ?
A proton accepter
B + H2O ⇔ ? + ?
HB+ + OH-
What is the equilibrium constant for a base ?
Give examples of strong and weak acids ?
Strong bases include any hydroxide of the Group 1A metals e.g. Na, K, Li etc...
The most common weak bases are ammonia and any organic amine.
Why is water amphoteric ?
It can act as an acid and a base
How does Ka relate to relative acid strength
The greater the magnitude of Ka, the stronger the acid (the more the reaction proceeds to the right).
What is a conjugate acid-base pair ?
The acid [HA] and the base produced when it ionises [A-].
E.g. HCN and CN-
Describe relative strength in conjugate acid-base pairs ?
If the main acid or base is strong, the conjugate acid or base will be weak, and vice versa.
Explain why an amino acid is an example of a conjugate acid-base ?
It has two groups, the acidic carbonyl group, and the base amine group.
Give a biological example of a Zwitterion ?
In blood plasma (pH 7.4) the predominant form of amino acids is COO-, NH3+
What is the ion product constant for water at STP ?
Kw = [H+] [OH-] = 1.0 x 10 -14
This is the equilibrium constant for the reaction in which water undergoes an acid-base reaction with itself.
What is the pH of a solution ?
An expression of the concentration of hydrogen ions in a solution.
pH = -log10[H+]
If the [H+] of solution of pure water is [H+] = 10-7, what is the pH ?
If pH is > 7, how is the solution described ?
If the pH is < 7, how is the solution described ?
How can pH be measured quantitatively and qualitatively ?
Quantitative = pH meter
Qualitative - indicator
What is the most commonly encountered weak acid ?
Acetic acid HOAc
If the Ka of an acid is 1.75 x 10 -15, what is the relative strength of the acid ?
N.B. Log 10=1, Log 1=0)
What is a salt ?
An ionic compound in which the anion is not OH-, or O2-, and the cation is not H+.
What is a neutralisation reaction ?
When acids and bases react with each other, forming a salt and water.
What is a Bronsted base ?
The salt of a weak acid
What is Kh of a salt ?
The hydrolysis constant of the salt.
What is the equation for a strong acid + a strong base ?
E.g. HCl + NaOH
HCl + NaOH ⇔ NaCl + H2O
N.B. Salts in which the cation and anion are both conjugates of a strong base and a strong acid form neutral solutions.
What is the equation for strong acid and a weak base ?
E.g. HCl + NH3
HCl + NH3 ⇔ NH4Cl
N.B. Salts that are formed based on a strong acid and a weak base for acidic solutions.
What is the equation for a weak acid and a strong base ?
E.g. HOAc + NaOH
HOAc + NaOH ⇔ NaOAc + H2O
What is the equation for a weak acid and a weak base ?
E.g. HOAc + NH3
HOAc + NH3 ⇔ NH4OAc
The pH is dependent on the relative strengths of the acid and the base
What is a buffer ?
A solution that resists change in pH when a solution is diluted , or a small amount of acid or base is added.
What does a buffer solution consist of ?
A mixture of a weak acid and its salt, or a weak base and its salt.
Why are buffers made up of weak acids/bases, and not strong ?
Strong acids/bases do not have any buffering capacity as the dissociation would be irreversible.
When is the buffering capacity of a solution at its maximum ?
When pH = pKa
What is an amphoteric species ?
A substance, e.g. water, that can act as either an acid or a base. Many metal oxides and hydroxides also act amphoterically.
What is the general purpose of a titration reaction ?
To determine the concentration of a given sample of acid or base (analyte).
What is the end/equivalent point of a titration ?
They are not always the same thing.
The end point is where a physical change in solution (e.g. colour) occurs.
The equivalence point is where a reaction is theoretically complete.
In practice, this difference can usually be seen as negligable.