Chapter 4 - Acids and redox Flashcards
What is an acid?
A substance which in an aqueous solution will release H+ ions
Why are acids referred to as proton donors?
They release a proton in the form of a H+ ion to ‘donate’ to a base
What is a strong acid?
A substance where every molecule of the acid is split up into H+ and a negative ion in aqueous solution. None of it exists as the whole molecule (100% ionised), it completely disassociates
What are the four main strong acids?
Hydrochloric, sulfuric, nitric, phopshoric
What is the equation for a strong acid in solution?
HA → H+ + A-
What is the equation for hydrochloric acid being ionised in solution?
HCl → H+ + Cl-
What is the equation for sulfuric acid being ionised in solution?
H2SO4 → H+ + HSO4-
What is the equation for nitric acid being ionised in solution?
HNO3 → H+ + NO3-
What is the equation for phosphoric acid being ionised in solution?
H3PO4 → H+ + H2PO4-
What is a weak acid?
A substance where only some of the acid molecules are split up into H+ and a negative ion in aqueous solution. Some of it still exists as the whole molecule, it partially disassociates
What is the equation for a weak acid being ionised in solution?
AH ⇌ H+ + A-
What are some examples of weak acids?
Carboxylic acids and most organic acids
What is a base?
A substance that neutralises an acid to form a salt
What is an alkali?
A base that dissolves in water to release hydroxide (OH-) ions into the solution
What is the word equation for a neutralisation reaction between an acid and an alkali?
acid + alkali → salt + water
What is the word equation for the reaction between an acid and metal oxide or hydroxide?
acid + metal oxide/hydroxide → salt + water
What is the word equation for the reaction between an acid and a metal carbonate?
acid + metal carbonate → salt + water + carbon dioxide
What is the ionic equation for a neutralisation reaction?
H+ + OH- → H2O
What is a titration?
A technique used to accurately measure the volume of one solution that reacts exactly with another solution
What can titrations be used for?
- finding the concentration of a solution
- identification of unknown chemicals
- finding the purity of a substance
What is a standard solution?
A solution of known concentration
When do you stop the repeats of a titration?
When the results are concordant (within 0.10 cm³ of each other)
What is an oxidation number?
The total number of electrons that an atom either gains or loses in order to form a chemical bond with another atom
What is the oxidation number for elements?
It is always zero
What are the rules for working out oxidation numbers?
- on simple ions, oxidation state = charge on ion
- in elements, oxidation state is always 0
- sum of oxidation numbers = total/overall charge
- in molecules, the more electronegative element is assumed to be the negative ion
- H is nearly always +1 and oxygen -2
What is the oxidation number of the Group 1 metals always?
+1
What is the oxidation number of the Group 2 metals always?
+2
What is usually the oxidation number of O, and what are the exceptions?
usually -2, except in peroxides and F2O
What is usually the oxidation number of hydrogen, and what are the exceptions to this?
usually +1, except in metal hydrides where it is -1
What is the oxidation number of fluorine always?
-1
What is the oxidation number of chlorine usually, and what are the exceptions to this?
usually -1, except in compounds with O or F
What is oxidation?
Oxidation can be defined as:
- the loss of electrons
- the addition of oxygen
- an increase in oxidation number
What is reduction?
Reduction can be defined as:
- the gain of electrons
- the removal of oxygen
- a decrease in oxidation number
What are redox reactions?
Redox reactions are ones involving both reduction and oxidation
What is a salt?
A substance where the H+ ion in the acid has been replaced by a metal ion (formed from reaction between acid and base)
