Topic 8 & 18 - Acids and bases Flashcards
Define Bronsted-Lowry acid and base
A Bronsted-Lowry acid donates a proton (BADP)
A Bronsted-Lowry base accepts a proton (BBAP)
Define Lewis acid and base
A Lewis acid accepts (a pair of) electrons (LAAE)
A Lewis base donates (a pair of) electrons (LBDE)
What are the requirements for a substance to be a Bronsted-Lowry acid or base?
An acid must be able to dissociate and release H+
A base must be able to accept H+ (must have a lone pair of electrons)
Deduce the conjugate acid and base pairs of a Bronsted-Lowry base and acid

What can we say about the relationship between Bronsted-Lowry and Lewis acids?
All Bronsted-Lowry acids are Lewis acids but not vice versa
What are alkalis?
Bases that dissolve in water to form OH-1
List four types of bases that are not hydroxides
- Metal oxides
- Ammonia
- (soluble) Carbonates
- Hydrogencarbonates
What is a universal indicator?
A mixture of several indicators that can be used to identify acids and bases on the whole pH scale
Define salt
The compound formed when the hydrogen of an acid is replaced by a metal or another positive ion
What are spectator ions in acid-base reactions?
Species that do not change during the reaction (can be cancelled out)
What is the reaction between acids and metals? Give three examples
Acid + metal → salt + hydrogen
2 HCl(aq) + Zn(s) → ZnCl2(aq) + H2(g)
H2SO4(aq) + Fe(s) → FeSO4(aq) + H2(g)
2 CH3COOH(aq) + Mg(s) → Mg(CH3COOH)2(aq) + H2(g)
What is the reaction between acids and bases? Give three examples
Acid + base → salt + water
HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)
HNO3(aq) + NH4OH(aq) → NH4NO3(aq) + H2O(l)
2 CH3COOH(aq) + CuO(s) → Cu(CH3COO)2(aq) + H2O(l)
What is the reaction between acids and carbonates? Give three examples
Acid + carbonate → salt + water + carbon dioxide
2 HCl(aq) + CaCO3(s) → CaCl2(aq) + H2O(l) + CO2(g)
H2SO4(aq) + Na2CO3(s) → Na2SO4(aq) + H2O(l) + CO2(g)
CH3COOH(aq) + KHCO3(s) → KCH3COO(aq) + H2O(l) + CO2(g)
Define effervescence
A reaction that gives off gas and produces visible bubbles (acid + metal, acid + carbonate)
Distinguish between strong and weak acids and bases
Strong acids and bases dissociate almost completely in solution.
Weak acids and bases only partially dissociate in solution.
What are three examples of strong acids?
- Hydrochloric acid, HCl
- Nitric acid, HNO3
- Sulfuric acid, H2SO4
What are three examples of weak acids?
- Ethanoic acid, CH3COOH
- Carbonic acid, H2CO3
- Phosphoric acid, H3PO4
What are four examples of strong bases?
- Lithium hydroxide, LiOH
- Sodium hydroxide, NaOH
- Potassium hydroxide, KOH
- Barium hydroxide, Ba(OH)2
What are two examples of weak bases?
- Ammonia, NH3
- Ethylamine, C2H5NH2
(other amines)
When are comparisons between the strength of acids and bases valid?
When the concentration and the temperature of the solutions are the same
List and describe three ways of distinguishing between strong and weak acids and bases
- Electrical conductivity
- Depends on the concentration of mobile ions
- Strong show higher conductivity than weak
- Can be measured by a conductivity meter or probe - Rate of reaction
- Strong will produce H+ ions at a faster rate than weak - pH
- The higher the H+ concentration, the lower the pH
What is the relationship between the concentration of H+ ions and pH?
pH = –log[H+]
[H+] = 10–pH
What is the change in [H+] when the pH changes by one unit?
A 10-fold change
What are values of pH for solutions that are acidic, neutral, and alkaline?
**Acidic **= pH < 7
**Neutral **= pH = 7
Alkaline (basic) = pH > 7
What is the expression for the ionic product constant of water (Kw)?
Kw= [H+][OH–]
Kw is dependent on?
Temperature
What is the relationship between the concentrations of H+ and OH–?
Inversely proportional
What is the pOH scale used for?
Describing the OH– concentration of solutions
What is the relationship between pOH and [OH–]?
pOH = –log[OH–]
[OH–] = 10–pOH
What is the relationship between pH and pOH at 25°C?
pH + pOH = 14
What is the relationship between pKw and Kw?
pKw = –log(Kw)
Kw = 10–pKw
What is the relationship between pH, pOH, and pKw?
pH + pOH = pKw
What are dissociation constants used for?
Expressing the strength of acids and bases
Define the acid dissociation constant
The greater the value of Ka, the greater the dissociation, and so the stronger the acid

Define the base dissociation constant
The greater the value of Kb, the greater the dissociation, and so the stronger the base

What is the relationship between Ka, Kb, and Kw?
Ka X Kb = Kw
What are the relationships between Ka and pKa and between Kb and pKb?
pKa = –logKa pKb = –logKb
Ka = 10–pKa Kb = 10–pKb
The relationship between Ka and pKa and between Kb and pKbis inverse
→ The larger the pKa, the weaker the acid
→ The larger the pKb, the weaker the base
What is the relationship between pKa, pKb, and pKw?
pKa + pKb = pKw = 14
What is a buffer solution?
A solution that resist the changes in pH on the addition of small amounts of acid or alkali
What are the two types of buffer solution?
- Acidic buffers that maintain the pH below 7
- Basic buffers that maintain the pH above 7
How is an acidic buffer made? Give an example
By mixing an aqueous solution of a weak acid with a solution of its salt of a strong alkali
CH3COOH(aq) + NaCH3COO(aq)
The mixture will contain high concentration of CH3COOH and CH3COO– (acid and conjugate base) that are ready to react with OH– and H+
Describe the reaction of CH3COOH + NaCH3COO buffer solution with acid
H+ combines with the base CH3COO– to for CH3COOH, decreasing the acidity
Describe the reaction of CH3COOH + NaCH3COO buffer solution with base
OH–combines with the acid CH3COOH to form CH3COO–and H2O2, removing the OH– ions.
How is a basic buffer made? Give an example
By combining a weak base with its salt of a strong acid
NH3(aq) + NH4Cl(aq)
Basic buffers work exactly the same way as acidic except the other way round
How are pH and pOH of a buffer solution determined?

How does dilution influence buffers?
Does not change the pH but lowers its buffering capacity
What factors can influence buffers?
Temperature and dilution
What happens to the pH in anion hydrolysis?
It increases
What happens to the pH in cation hydrolysis?
It decreases
Outline the possible hydrolysis combinations and the nature of their salts
- Strong acid + strong base = neutral salt
- Weak acid + strong base = basic salt
- Strong acid + weak base = acidic salt
What is the equivalence point?
The point when stoichiometrically equivalent amounts of acid and base have been reacted together. At this point the solution contains only salt and water.
Give an example and draw the titration curve of the reaction of a strong acid and strong base
HCl + NaOH → NaCl + H2O

Give an example and draw the titration curve of the reaction of a weak acid and strong base
CH3COOH + NaOH ⇔ NaCH3COO + H2O

Give an example and draw the titration curve of the reaction of a strong acid and weak base
HCl(aq) + NH3(aq) ⇔ NH4Cl(aq)

Give an example and draw the titration curve of the reaction of a weak acid and weak base
CH3COOH(aq) + NH3(aq) ⇔ CH3COONH4(aq)

Describe the action of an acid-base indicator
HIn(aq) ⇔ H+(aq) + In–(aq)
- Weak acids or weak bases in which the undissociated and dissociated forms have different colours
- HIn has colour A and In– has colour B
- H+ concentration determines to which side the equilibrium shifts and thus changes colour
When do indicators change colour?
When the pH is equal to their pKa (the end point)
Ka = [H+] or pKa = pH
What can indicators be used for in titrations?
To identify the equivalence point