Acids and Bases Flashcards
Define a Bronsted-Lowry acid.
A proton donor.
Define a Bronsted-Lowry acid.
A proton donor.
Define a Bronsted-Lowry base.
A proton acceptor.
When acids and bases react, what happens to the protons?
They are transferred from the acid to the base.
Is water an acid or a base?
It can act as both.
Give an example of a strong acid and explain why it is classified as such.
HCl, because it almost completely dissociates in water. For the sake of calculation, we assume it dissociates completely.
Give an example of a strong base and explain why it is classified as such.
NaOH, because it almost completely dissociates in water. For the sake of calculation, we assume it dissociates completely.
Give an example of a weak acid and explain why it is classified as such.
CH3COOH, because it only dissociates slightly in water. Only small numbers of H+ ions are formed. It forms an equilibrium that lies well over to the left.
Give an example of a weak base and explain why it is classified as such.
NH3, because it only dissociates slightly in water. Only small numbers of OH- ions are formed. It forms an equilibrium that lies well over to the left.
What happens when a strong or weak acid is added to water?
Water acts as a base and accepts the proton, forming H3O+ ions. This is an equilibrium.
What equilibrium exists in water?
2H2O –> H3O+ + OH- or
H2O –> H+ + OH-
These are equilibriums that lie well over to the left.
What is Kw?
The ionic product of water.
Why does Kw exist?
Because water only dissociates very slightly, we take the concentration of water to be constant. If we use the equation for Kc, and multiply it by [H2O], this gives us another constant.
What is the equation for Kw?
Kw = [H+][OH-] or, in pure water, Kw = [H+]^2
What are the units of Kw?
mol^2 dm^-6
What is the value of Kw at 298K?
1.00x10^-14
What condition affects Kw?
Temperature.
How can we calculate the pH of a strong base from it’s concentration?
There is one mole of OH- ions for every one mole of the base, assuming it dissociates completely in water. So, [OH-] = [B]. We can then use the equation for Kw to calculate [H], and use this to calculate the pH.
Give the equation for pH.
pH = -log10[H+]
What do square brackets represent?
Concentration in mol dm^-3
Define a monoprotic acid.
Each molecule of acid will release one proton when it dissociates.
Define a diprotic acid.
Each molecule of acid will release two protons when it dissociates.
How can we calculate the pH of a strong monoprotic acid from it’s concentration?
Assuming the acid completely dissociates in water, the H+ concentration is the same as the acid concentration. We then use this to calculate pH.
How can we calculate the pH of a strong diprotic acid from it’s concentration?
Assuming the acid completely dissociates in water, the H+ concentration is double the acid concentration. We then use this to calculate pH.
What is Ka?
The acid dissociation constant.
What are the units of Ka?
mol dm-3
Give an expression for Ka.
Ka = [H+][A-] all over [HA] or, Ka = [H]^2 over [HA] (assuming all the H+ ions come from the acid, [H+] = [A-])
Give the equation for pKa.
pKa = -log10(Ka)
What indicator would you use for a strong acid-strong base titration?
Methyl orange or phenolphthalein.
What indicator would you use for a strong acid-weak base titration?
Methyl orange
What indicator would you use for a weak acid-strong base titrarion?
Phenolphthalein
What indicator would you use for a weak acid-weak base titration?
No indicator will work, because there’s no sharp pH change.
Define a Bronsted-Lowry base.
A proton acceptor.
When acids and bases react, what happens to the protons?
They are transferred from the acid to the base.
Is water an acid or a base?
It can act as both.
Give an example of a strong acid and explain why it is classified as such.
HCl, because it almost completely dissociates in water. For the sake of calculation, we assume it dissociates completely.
Give an example of a strong base and explain why it is classified as such.
NaOH, because it almost completely dissociates in water. For the sake of calculation, we assume it dissociates completely.
Give an example of a weak acid and explain why it is classified as such.
CH3COOH, because it only dissociates slightly in water. Only small numbers of H+ ions are formed. It forms an equilibrium that lies well over to the left.
Give an example of a weak base and explain why it is classified as such.
NH3, because it only dissociates slightly in water. Only small numbers of OH- ions are formed. It forms an equilibrium that lies well over to the left.
What happens when a strong or weak acid is added to water?
Water acts as a base and accepts the proton, forming H3O+ ions. This is an equilibrium.
What equilibrium exists in water?
2H2O –> H3O+ + OH- or
H2O –> H+ + OH-
These are equilibriums that lie well over to the left.
What is Kw?
The ionic product of water.
Why does Kw exist?
Because water only dissociates very slightly, we take the concentration of water to be constant. If we use the equation for Kc, and multiply it by [H2O], this gives us another constant.
What is the equation for Kw?
Kw = [H+][OH-] or, in pure water, Kw = [H+]^2
What are the units of Kw?
mol^2 dm^-6
What is the value of Kw at 298K?
1.00x10^-14
What condition affects Kw?
Temperature.
How can we calculate the pH of a strong base from it’s concentration?
There is one mole of OH- ions for every one mole of the base, assuming it dissociates completely in water. So, [OH-] = [B]. We can then use the equation for Kw to calculate [H], and use this to calculate the pH.
Give the equation for pH.
pH = -log10[H+]
What do square brackets represent?
Concentration in mol dm^-3
Define a monoprotic acid.
Each molecule of acid will release one proton when it dissociates.
Define a diprotic acid.
Each molecule of acid will release two protons when it dissociates.
How can we calculate the pH of a strong monoprotic acid from it’s concentration?
Assuming the acid completely dissociates in water, the H+ concentration is the same as the acid concentration. We then use this to calculate pH.
How can we calculate the pH of a strong diprotic acid from it’s concentration?
Assuming the acid completely dissociates in water, the H+ concentration is double the acid concentration. We then use this to calculate pH.
What is Ka?
The acid dissociation constant.
What are the units of Ka?
mol dm-3
Give an expression for Ka.
Ka = [H+][A-] all over [HA] or, Ka = [H]^2 over [HA] (assuming all the H+ ions come from the acid, [H+] = [A-])
Give the equation for pKa.
pKa = -log10(Ka)
What indicator would you use for a strong acid-strong base titration?
Methyl orange or phenolphthalein.
What indicator would you use for a strong acid-weak base titration?
Methyl orange
What indicator would you use for a weak acid-strong base titrarion?
Phenolphthalein
What indicator would you use for a weak acid-weak base titration?
No indicator will work, because there’s no sharp pH change.
What is the point at which you have enough acid/alkali for neutralisation called?
Equivalence point.
How do diprotic acids nuetralise?
In two stages.
What does a titration curve with a diprotic acid look like?
It has two equivalence points.
Define a buffer.
A solution that resists changes in pH when small amounts of acid or alkali are added.
How do you make an acidic buffer?
Mix a weak acid with a salt of the acid (usually sodium).
Give the equation for an acidic buffer.
Weak acid –> H+ + acid ion (from the salt). This is an equilibrium.
What happens when you add small amounts of acid to an acidic buffer?
The H+ concentration will increase. Most of the extra H+ ions react with the acid ion to form the acid, shifting the equilibrium to the left and therefore restoring the H+ concentration to near it’s original value, so the pH doesn’t change.
What provides the large number of acid ions in an acidic buffer?
The salt of the acid completely dissociating.
What happens if a small amount of base is added to an acidic buffer?
The OH- concentration increases. Most of these ions react with the H+ ions to form water - removing H+ ion. This causes the equilibrium to shift to the right to produce more H+ ions, restoring the solution to near it’s original pH.
What provides the large number of acid molecules in an acidic buffer?
The weak acid barely dissociating.
How do you make a basic buffer?
Mix a weak base with the salt of that base (usually chlorine).
Give the equation for a basic buffer.
base + water –> +ve base ions + OH-
This is an equilibrium.
What provides the large amounts of +ve base ions in a basic buffer?
The basic salt completely dissociating
What provides the large amounts of base molecules in a basic buffer?
The weak base barely dissociating.
What happens to a basic buffer if small amounts of a base are added?
The OH- concentration increases. Most of these will react with the +ve base ions to form the base and water. The equilibrium will shift to the left, removing extra OH- ions from the solution, restoring the solution to near it’s original pH.
What happens to a basic buffer if small amounts of acid are added?
The H+ concentration will increase. Most of these will react with the OH- ions to from water. The equilibrium will then shift to the right to replace these OH- ions, restoring the solution to near it’s original pH.
Give an application of buffers.
Blood, shampoo, biological washing powders.
