Acid & Bases Flashcards
What are ssome common acids and their uses?
Acetic acid - flavouring; preservative
Citric acid: flavouring
Phosphoric acid: rest remover
Boric acid: ,o;d amtosptic/insecticide
Hydrochloric acid: Brick / ceramic tile cleaner
Sodium hydroxide: oven cleaner
Ammonia: Household cleaner
Sodium carbonate: Water softener, grease remover
sodium hydrogen carbonate: Fire extinguisher, backing powder
What does Arrhenius define an acid as?
H+ producer in aqueous solution
What does Arrhenius define a base as?
OH- produced in aqueous solution
What does Bronsted Lowry define an acid as?
Proton (H+) donor
What does Bronsted Lowry define a base as?
Proton (H+) acceptor
What is H+?
H+ is short for H3O+ in the reaction which is hydronium
What is a strong acid/base?
A strong acid or base has equilibrium to the right (I.e. it is fully ionised/dissociatied). (Complete dissociation)
What is a weak acid/base?
A weak acid or base has equilibrium to the left (partial ionisation/dissociation)
What is Ka and Kb?
The acid dissociation constant (Ka) is a quantitative measure of the strength of an acid in solution while the base dissociation constant (Kb) is a measure of basicity—the base’s general strength.
Uses the same formula as in Keq, and ignore liquid and solid states
What is a conjugate acid
A conjugate acid, within the Brønsted–Lowry acid–base theory, is a chemical compound formed when an acid gives a proton (H +) to a base—in other words, it is a base with a hydrogen ion added to it, as it loses a hydrogen ion in the reverse reaction.
I.e. NH4+ is the conjugate acid of NH3
What is a conjugate base
A conjugate base is basically an acid that lost its hydrogen ion. Its formula is the acid formula, minus the hydrogen ion.
I.e. NH3 is the conjugate base of NH4+
What is meant by the autoionisation of water?
It is the ability of water to react with itself and form a hydronium and hydroxide ion. The ability of water to react with itself is known as autoionisation.
What is the ionisation/equilibrium constant for autoionisation of water?
Kw = 10^-14 = [H3O+][OH-]
What is [H+] in a neutral solution?
[H+] = [OH-] = 1.0 x 10^-7
What is [H+] in a acidic solution?
[H+] > 1.0 x 10^-7
What is [H+] in a basic solution?
[H+] < 1.0 x 10^-7
What is the pH equation?
-log[H+]
What is the pOH equation?
-log[OH-]
What is the relationship between pH and pOH?
pH + pOH = 14
What pH is acidic?
pH < 7
What pH is neutral?
pH = 7
What pH is basic?
pH > 7
What is a strong acid or base?
these completely ionise in water
Equilibrium is completely to the right –> Ka or Kb = infinity
What are some examples of strong acids (6)
H2SO4 (Sulfuric acid)
HCl (Hydrochloric acid)
HBr(Hydrobromic acid)
HI ( Hydroiodic acid)
HNO3 (Nitric acid)
HClO4 (Perchloric acid)
What are some examples of strong bases?
All hydroxides of groups 1 and 2 except for Be
If there is 0.1M of a strong acid/base, what would the concentration of the hydroxide or hydronium ions be after dissociation (assuming it is monoprotic)
0.1M as well
What is a weak acid/base?
If they are weak, they don’t completely ionise in water (partially ionise/dissociate)
How do we calculate pKa?
-log(Ka)
How do we calculate pKb?
-log(Kb)
What is the relationship between Ka and pKa?
The larger the value of Ka, the stronger the acid and the lower the value of pKa
Can we assume small change? What is the condition (rarely needed)
Yes we can assume small change, however, the general accepted rule is that small change needs to be maximum 5% of the original subtraction (i.e. 0.1-x, it can be a maximum of 0.005)
What is the relationship between Ka, Kb and Kw?
Ka x Kb = Kw = 10^-14
What is the relationship between pKa and pKb?
pKa + pKb = 14
Why does Ka decrease as we remove hydrogens?
because ionization happens in steps because as protons are removed, the remaining negatively charged ions experience increased repulsion, making it harder to remove additional protons
Harder to remove charge against increased negative charge
How can you tell if a salt is an acidic, neutral or basic given that it is a salt of a weak acid or base?
We look at what creates the salt. If there is a strong acid/base, the salt will be a acid/basic depending on which one was strong in creating the salt. I.e. for NH4Cl, it is a salt of NH4OH (weak base) and HCl (strong acid)
As the acid “wins”, the pH < 7 –> the salt is acidic
However, the more refined:
What are the general rules for acidic, neutral or basic salts?
Whenever an acid and a base react, they have the potential to form a salt. For example, when sodium hydroxide reacts with hydrochloric acid in water, they form sodium chloride, a salt. Salts come in three different forms: basic salts, neutral salts and acid salts. When a strong base reacts with a strong acid, a neutral salt is formed. When a strong base reacts with a weak acid, a basic salt is formed. When a strong acid reacts with a weak base, an acidic salt is formed.
What is the school’s method of classifying a certain salt as either acidic, neutral or basic?
- State what the salt ionises to form
- State which ion is neutral (which can be determined by which came from a strong acid or base), and state that it cant hydrolyse further
- State that the other ion (which came from a weak acid or base) comes from a certain weak acid or base, and that it will undergo hydrolysis in water
- Concluding statement: Excess OH- or H+ in solution makes solution (basic/acidic). Thus pH is greater or less than or equal to 7 (depending)
What is the common ion effect?
Used to describe the effect on an equilibrium when one or more species in the reaction is shared with another reaction –> results in shifting equilibrium properties
I.e. when an ion is the same as ions already existing in the equilibrium reaction
Adding a common ion prevents the weak acid or weak base from ionizing as much as it would without the added common ion. The common ion effect suppresses the ionization of a weak acid by adding more of an ion that is a product of this equilibrium.
What is a buffer system?
It is a solution containing both a weak acid/base and its conjugate acid/base on opposite sides of the reaction. Buffer systems are able to withstand changes in pH when acid or base (limited amounts) are added
How do we do buffer system and pH change questions, where a random substance is added?
Technically we use two ice tables, where the thing that is added is used up, and the system shifts to adjust for this, and each reactant and product is adjusted for this (check example in ppt 31)
And then solve the next ice table kind of thing
What is the Henderson hasselbach equation?
pH = pKa + log ([initial base] / [initial acid])
What is the condition for the ideal buffer capacity?
pH = pKa
What is buffer capacity?
It is the amount of strong acid or base that can be added without causing a significant pH change
What can optimise buffer capacity?
Highest when [HA] and [A-] are large
Highest when [A] = [A-]
Most effective buffers have acid/base ratio less than 10 and more than 0.1 –> pH range is +- 1
Why are buffers important in natural systems?
Biological systems such as blood contain buffers:
pH control is essential because biochemical reactions are very sensitive to pH
What is the ideal pH of human blood?
It is slightly basic, pH = 7.39 - 7.45
What are dangerous levels of pH in the human blood?
pH < 7.2 = acidosis
pH > 7.6 = alkalosis
Death occurs for pH less than 6.8 or greater than 7.8
What are the buffer systems involved in the blood?
Extracellular buffer:
H+ (aq) + HCO3 (aq) ⇌ H2CO3 (aq)
H2CO3 (aq) ⇌ H2O (l) + CO2 (g)
pH can be reduced by:
H2CO3 (aq) + OH- (aq) ⇌ HCO3- (aq) + H2O (l)
CO2 + H2O ⇌ H2CO3 ⇌ H+ + HCO3-