Acids and Bases 2

Question 1

Ionic equations

Answer 1

● Equations that only show the chemical species that have participated in the
reaction (such as ions and molecules).

● Ions that are chemically unchanged for the entire process are called spectator
ions - they can be removed from the equation.

● Like typical chemical symbol equations, ionic equations must be balanced.
The resulting (net) ionic equation should be as simple as possible.

Question 2

Single replacement - Displacement reactions

Answer 2

● Reactions between reactive metals and acids are single replacement reactions.

Mg (s) + 2 HCl (aq) → MgCl2
(aq) + H2 (g)

● The metal is more reactive than hydrogen so it displaces hydrogen
from its compound.

Question 3

Double replacement - precipitation

Answer 3

solution AB + solution CD → precipitate AC + solution BD

When two aqueous ionic solutions are mixed together, if an insoluble
ionic compound is produced, a precipitate will be formed.

During the process, the cations and the anions of the two solutions are
exchanged.

Question 4

Supernate

Answer 4

It is a solution which remains above a precipitate

Question 5

precipitate

Answer 5

it settles and falls to the bottom of the solution

Question 6

Precipitation of silver chloride

When colorless silver nitrate solution is added to colorless sodium chloride
solution

Answer 6

white precipitate of silver chloride is produced.

Overall equation: AgNO3
(aq) + NaCl (aq) –> AgCl(s) + NaNO3
(aq)
Ionic equation: Ag+
(aq) + Cl-(aq) –> AgCl(s)

Question 7

what is concentration

Answer 7

Concentration refers to the amount (number of moles) of solute dissolved in a
unit volume (dm3) of solution.

Unit: mol dm^-3

Question 8

what does the strength mean in acids and bases

Answer 8

Strength refers to the degree / extent of dissociation of the acid/ base when
dissolved in water.

Question 9

strong acids

Answer 9

Hydrochloric acid HCl
Sulphuric acid H2SO4
Nitric acid HNO3

Question 10

strong bases

Answer 10

Group 1 metal hydroxides
- Sodium hydroxide NaOH
- Potassium hydroxide KOH

Barium Hydroxide
- Ba(OH)2

Question 11

what happens when strong acids dissociate in water

Answer 11

They dissolve completely or fully in water

Question 12

weak acid

Answer 12

Ethanoic acid CH3COOH
Carbonic acid H2CO3

Question 13

weak base

Answer 13

Ammonia NH3

Question 14

concentration vs strength

Answer 14

Concentration = number of moles found in 1
dm3 of solution.

Strength = Degree of dissociation of acid in
aqueous solution

Question 15

Organic acids

Answer 15

Organic acids are acidic because they contain COOH group. They are weak acids.

propanoic acid - monoprotic
oxalic acid - diprotic
citric acid - triprotic

Question 16

dissociation of carbonic acid

Answer 16

● Carbonic acid is an aqueous solution of carbon dioxide.

● It is formed by bubbling CO2 (g) in water:

CO2 (g) + H2O (l) ⇌ H2CO3 (aq)
● Dissociation: H2CO3 (aq) ⇌ H+ (aq) + HCO3-(aq)

● To write the equation for the dissociation of acids or bases in water, we use “→” for strong acids and bases, but we use “⇌” for weak acids and bases

Question 17

Comparing strength of acids / bases (1)

Answer 17

1. Extent of dissociation - the stronger the acid / base, the larger the extent of
   dissociation.

● Strong acid fully dissociates: HCl (aq) → H+ (aq) + Cl- (aq)

● Weak acid partially dissociates: CH3COOH (aq) ⇌ CH3COO- (aq) + H+ (aq)

With the same concentration of acid/ base, the ion concentration of a strong acid/
base is higher.

● With the same concentration of acids, the H
+ ion concentration of a stronger acid
is larger.

○ The pH of 1M HCl(aq) is lower than the pH of 1M CH3COOH(aq)

● With the same concentration of bases, the OH-
ion concentration of a stronger
base is larger.

○ The pH of 1M NaOH(aq) is higher than the pH of 1M NH3
(aq)

Question 18

Comparing strength of acids / bases (2)

Answer 18

Vigor of reaction - under same concentration, the stronger the acid or base, the more vigorous the reaction and the faster the reaction rate.

● Reactions between stronger acids and metals / metal carbonates - rate of
bubble production is higher

● Reaction between stronger acids and bases - more heat produced and
greater temperature change

Question 19

Comparing strength of acids / bases (3)

Answer 19

Electrical conductivity - it depends on the presence of mobile ions in the solutions.

● Stronger acids / bases have higher concentration of mobile ions in the solution, causing the electrical conductivity to be higher.

● This can be tested by connecting the solution in a complete circuit with a light
bulb and observe its brightness, or measure the current using an ammeter.