Unit 1.2 Acids and Bases Flashcards
Unit 1: Physical Chemistry
What is a dative or coordinate bond?
A covalent bond in which one of the atoms supplies both of the electrons
What is Kw
The dissociation constant of water
= 1.01x10-14 (at 25)
What is Arrhenius’s theories for acids and bases?
Acids- substances that produce H+ ions in solution
Bases- substances that produce OH- ions in solution
What is Bronsted-Lowry’s theory for acids and bases?
Acids- proton (H+) doners
Bases- Proton (H+) acceptors
What is a conjugate base?
The substance left after a acid donates its proton
What is a conjugate acid?
The substance that gains the proton
How does a stronger or weaker acid effect the conjugate base and acid?
The stronger the acid the weaker the conjugate base
The stronger the base the weaker the conjugate acid
What is an amphoteric substance?
These are substances that can react as an acid or base
What is an example of an amphoteric substance?
Water
What does pH stand for?
Potential of hydrogen
As the [H3O+] increases what happens to the pH?
The pH decreases
What is the pOH- of a solution measure?
[OH-]
What expression is used to calculate the [H+] when the pH is known?
[H3O+]=-Log10^-pH
What is the expression for calculating pOH?
pOH=-log10[OH-]
What is the definition for a strong acid?
An acid that completely dissociates into ions in aqueous solution and is therefore in a equilibrium with a high Ka
What are examples of strong acids?
-Hydrochloric acid
-Nitric acid
-Sufuric acid
What happens when you dilute a strong acid by a factor of 10?
The pH will change by 1 unit
What is the definition for a weak acid?
An acid that only partially dissociates in solution and is therefore in equilibrium with a low Ka
What are examples for weak acids?
-Carbonic acid
-Sulphurous acid
What does Ka mean?
The acid dissociation constant
What value is assigned to water in Ka?
1
What does a higher Ka mean?
There is a stronger more dissociated acid
What does a low and high Ka indicate?
High Ka- a strong acid
Low Ka- a weak acid
What is the expression to find the pH for a strong acid?
pH= -log10[H3O+] so
[H3O+]=10^-pH
What is the expression to find the pKa for a weak acid?
pKa= -log10Ka so Ka=10^-pKa
What is a Polyprotic acid?
Proyprotic acids have more than one ionisable proton. The protons are removed one by one, not all at once
Which stage is the easiest when removing protons in polyprotic acid?
The first proton
What does it mean if the acid is equimolar?
They contain the same number of moles per litre
What does it mean if the acids are monoprotic?
They both release one H+ per molecule
How does a pH value work with a base which doesn’t have H+ ions?
-Every water based solution sets up an equilibrium
-If additional hydroxide ions are present
-The [H+] will decrease to below that of water
-pH is a measure of the conc of theses [H+] ions
What is a weak base?
They only partially dissociated into ions in aqueous solution
Examples of weak base?
Ammonia and amines
How is a salt produced?
A substance that is produced when H+ ion of an acid is replaced by a positive ion, usually a metal
What happens when a strong acid fully neutralises a strong base?
The pH of the salt solution will always be 7 at 25C
Do strong bases and strong acids affect the water dissociation?
It does not affect the water dissociation equilibrium so there are equal concentrations of H+ and OH- ions in solution and pH=7
Strong acid/strong base salt pH?
=7
Strong acid/ weak base salt pH?
<7
Weak acid/ Strong base salt pH?
> 7
Weak acid/ Weak base salt pH?
Approximately 7
What is the end point of a reaction?
The point in a titration that is shown by a change in colour
What is an equivalence point?
The point in a neuralisation reaction when the moles of base = moles of acid so the solution only contains salt and water (neutral)
What do indicators change colour in response too?
pH
What is KIn?
Acid dissociation constant for indicators
What pH of an indicator should be chosen for a strong acid / strong base?
One will a pKIn value one less than the pH of the equivalent point , If using a strong base against strong acid it should be one greater than the pH at the equivalent point
What pH of an indicator should be used for a weak acid / strong base?
pH ~ 7.5
What is a buffer solution?
A solution in which the pH remains approximately constant when small volumes of acid, base or water are added
What is an acid buffer made from?
A weak acid and one of its salts from a strong base
The salt will supplies the conjugate base of the acid
What does the pH of an acid buffer depend on?
The Ka of the weak acid and the ratio of [acid] to [conjugate base] (salt)
How can you change the pH of a buffer?
By changing the ratio of acid to salt, or by choosing a different acid and one of its salts
How is a basic buffer solution prepared?
A basic buffer consists of a solution of a weak base and one of its salts
How does a buffer maintain a constant pH on the addition of acid?
If a small amount of acid is added to the buffer, the weak base removes the excess H+
What happens to the pH of a buffer when water is added?
The ration remains unchanged between the base and its salt so the pH stays the same
