Chapter 4 (2.1.4/5) Flashcards
Rules of oxidation numbers
- always 0 for elements
- in a pure element, bonding is to atoms of the same element
- each atom in a compound has an oxidation number
- number has a sign placed before it
- numerically the same as the ions charge, some exceptions
- sum of oxidation numbers = total charge
Special cases for oxidation numbers
- H in metal hydrides: -1
- O in peroxides: -1
- O bonded to F: +2
Roman numerals
- indicate magnitude of oxidation number when an element may have compounds/ions with different oxidation numbers
Oxidation
- addition of oxygen
- loss of electrons
- increase in oxidation number
Reduction
- removal of oxygen
- gain of electrons
- decrease in oxidation number
What is a salt?
When the H+ ion in an acid is replaced by a metal ion or an ammonium ion.
Define an acid
Proton donor
Define a base
Proton acceptor
Formula of common acids: hydrochloric, sulfuric, nitric, ethanoic
- HCl
- H2SO4
- NO3
- CH3COOH
Formula of common bases: sodium hydroxide, potassium hydroxide, ammonia
- NaOH
- KOH
- NH3
What happens when acids dissolve in water?
They release H+ ions into the aqueous solution
What happens when an alkali dissolves in water?
They release OH- ions into the aqueous solution
What is an alkali?
A water-soluble base
What is a strong acid?
A strong acid releases all its hydrogen atoms into solution as H+ ions and completely dissociates in aqueous solution
What is a weak acid?
A weak acid only releases a small proportion of its available hydrogen atoms into solution as H+ ions and partially dissociates in aqueous solution. (double arrow used in equations)
Name general examples of bases
- metal oxides
- metal hydroxides
- metal carbonates
- ammonia
Neutralisation reaction
H+ (aq) + OH- (aq) –> H2O (l)
General equations for neutralisation of acids
acid + metal oxide/hydroxide –> salt + water
acid + alkali –> salt + water
acid + metal carbonate –> salt + water + carbon dioxide
acid + metal –> salt + hydrogen
How do you prepare a standard solution?
- accurately weigh solid
- dissolve in distilled water
- transfer to volumetric flask
- add more distilled water to graduation line
- slowly invert flask several times to mix
Percentage uncertainty formula
uncertainty/capacity X 100
Percentage purity formula
mass of pure/mass of impure X 100
Describe a titration
- add a measured volume of unknown concentration solution to a conical flask using a pipette
- add solution of known concentration to burette and record initial reading
- add a few drops of indicator
- run solution and swirl the flask. stop at endpoint
- record final reading and calculate titre
- using the rough titre, repeat the titration but now adding solution in a dropwise manner as endpoint is approached. repeat until 2 concordant results are obtained.
What is a disproportionation reaction?
A reaction in which the same element is reduced and oxidised
