Acids and Bases, Ionic Equations

Question 1

Reactivity Series

Answer 1

Please - Potassium
Stop - Sodium
Complaining - Calcium
My - Magnesium
Aluminium - Aluminium
Zipper - Zinc
Is - Iron
Too - Tin
Loose. - Lead
Help - Hydrogen
Correct - Copper
My - Mercury
Spoiled - Silver
Gown. - Gold

Question 2

Acid

Answer 2

An acid is a substance that ionises/dissociates
in water to form H+ ions.

E.g.
H2SO^4 (aq) → 2H+ (aq) + SO4^2− (aq)

• Always simple covalent

Hydrochloric acid: HCl, s, m
Nitric acid: HNO3, s, m
Sulfuric acid: H2SO4, s, d
Phosphoric acid: H3SO4, w, t
Ethanoic acid: CH3COOH, w, m
Carbonic acid: H2CO3, w, d

Question 3

Strength (of Bases), Concentration, Basicity of Acids

Answer 3

Strength (Degree of dissociation/ionisation of acids & bases)
- Strong acid/base: fully dissociates/ionises in water to produce lots of H+/OH- ions.
- Weak acid/base: partially dissociates/ionises in water, some ions recombine and remain as molecules

Concentration (Amount of solute in solution)
- Concentrated acid (E.g. HCl): a lot of HCl dissolved in given vol. of H2O
- Diulte acid (E.g. dilute HCl): little HCl dissolved in given vol. of H2O

Basicity (Max. no. of H+ ions formed when a molecule of acid ionises in water)
- Monobasic: Produce 1 H+ ion per molecule of the acid. (1:1)
- Dibasic: Produce 2 H+ ions per molecule of the acid. (2:1)
- Tribasic: Produce 3 H+ ions per molecule of the acid. (3:1)

Question 4

Role of Water (In Acidity)

Answer 4

• Acids dissolve and ionise in water (not organic solvents) to produce hydrogen ions
• Hydrogen ions are responsible for acidic properties
• Hence only exhibit acidic properties when they are dissolved in water

Question 5

Base

Answer 5

A base is a substance that reacts with an acid to form salt and water only. (neutralisation reaction).
Generally, bases are metal oxides or hydroxides e.g. sodium oxide, barium hydroxide, etc.

• Alkali: Soluble bases that ionise/dissociate in water to form hydroxide ions.
• Salt: A salt is a substance that is formed when the hydrogen ion (H+) of an acid is replaced by a metal ion or an ammonium (NH4^+) ion.

Sodium hydroxide: NaOH, s
Potassium hydroxide: KOH, s
Barium hydroxide: Ba(OH)2, s
Aqueous ammonia: NH3, w, partially dissociate

Question 6

Chemical properties of acids and alkalis

Answer 6

Property 1: Acids + reactive metals -> salt + h2
Property 2: Acids + metal carbonates -> salt + co2 + h2o
Property 3: Acids + metal oxides / hydroxides -> salt + h2o (neutralisation)
- H+ (aq) + OH- (aq) -> H2O (l)

Property 1: Alkalis + acids -> salt + h2o (neutralisation)
- H+ (aq) + OH- (aq) -> H2O (l)
Property 2: Alkalis + ammonium salts -> ∆ (heat is added) salt + h2o + nh3 gas.

Question 7

Ionic Equations

Answer 7

Purpose: An ionic equation shows only the chemical species that are involved in a reaction, shows how ions present are reacting

Question 8

Oxides

Answer 8

Metallic oxides
- Basic oxides react with acids to form salt and h2o;
- ALL METALS, exceptions in amphoteric

• Acidic oxides react with alkalis to form salt and h2o;
• NON-METALS; s2, co2, p2o5

Non-metallic oxides
- Amphoteric oxides react with both acids and alkalis to form salt;
- Al2O3, PbO, ZnO (Aluminium, lead, zinc)

• Neutral oxides do not react with either acids or alkalis;
• GASES; co2, h2o, no

Question 9

pH scale

Answer 9

• acid <7, alkali >7; 0-14
  1. 0-3 strong acid
  2. 4-6 weak acid
  3. 8-10 weak base
  4. 11-14 strong base

Question 10

titration curve

Answer 10

• determines conc. of substances
• start pt. & end pt. deduce strength of acid + alkali
• check that end-pt lies in range of suitable indicator; SOME DON’T HAVE

Question 11

importance of pH

Answer 11

• important control soil pH bc affects growth & development of plants
• most plants grow best when pH neutral/slightly acidic
• CANNOT grow if soil TOO ACIDIC when too much fertiliser added & leeches soil nutrients
• also can be due to acid rain

to remove, add: CALCIUM oxide (lime)/hydroxide (slaked lime)/carbonate
- carbonate best: cheapest, will NOT make soil alkaline