2.1.4 Acids + 2.1.5 Redox

Question 1

Strong acid

Answer 1

Completely dissociates in aqueous solution to release all of its H+ ions
E.g. HCl → H+ + Cl-

Question 2

Weak acid

Answer 2

Partially dissociates in aqueous solution to only release a small proportion of H+ ions
E.g. CH3COOH ⇌ H+ + CH3COO-
- Most organic acids are weak acids

Question 3

Base

Answer 3

Bases neutralise an acid to form a salt and water
acid + base → salt + water
H+ + OH- → H2O
- Alkali is a base that dissolves in water to release OH- ions into solution
- Carbonates neutralise acids to form salt, water and carbon dioxide gas
acid + metal carbonate → salt + water + carbon dioxide (g)
H+ + CO3 → H2O + CO2

Question 4

Acid-base titration

Answer 4

1) Fill burette with acid until the O mark and record initial burette reading (nearest 0.05cm3) - make sure there are no air bubbles
2) pipette measured volume (25cm3) of base solution to conical flask and add indicator solution (methyl orange) into conical flask
3) open the tap and add the acid to the base one drop at a time, swirling in between until first permanent colour change achieved
4) record final burette reading (read from bottom of meniscus at eye level) and use as rough aim
5) repeat the process until you get concordant titres (within 0.1cm3) and calculate the mean titre

Question 5

Titration calculations

Answer 5

n = c x v

Amount (mols) = Concentration (mol/dm3) x Volume (dm3)

Question 6

Reduction

Answer 6

Removal of oxygen
Gain of electrons
Decrease in oxidation number

Question 7

Oxidation

Answer 7

Addition of oxygen
Loss of electrons
Increase in oxidation number