Acids and Redox (F6examonly) Flashcards
(22 cards)
What are strong acids in terms of relative dissociation?
acids that dissociate nearly fully in water – nearly all the H+ ions are released
What are weak acids in terms of relative dissociation?
acids that only partially dissociate in water – only some H+ ions are released
What are titrations?
a technique used to accurately measure the volume of one solution that reacts exactly with another solution
What are titrations used for?
- finding the concentration of a solution
- identifying unknown chemicals
- finding the purity of a substance
Burette readings must be measured to the nearest…
0.05 cm3 (the reading must have two decimal places and end in a 0 or a 5)
What is a titre?
the volume of solution added from the burette (the volume of solution you let out of the tap)
Do titres need to be concordant? What does this mean?
yes, it means that the results are within 0.10 cm3 of each other
When working out the mean titre, how do you ensure it is accurate?
by only using concordant titres (within 0.10 cm3 of each other), and rejecting the inaccurate titres
How do you do titration calculations?
see notes (and do pass paper qs)
What is an oxidation number?
a number that tells you how many e- an atom has donated or accepted to form an ion/a part of a compound
What are the rules involving oxidation numbers for elements?
all pure elements have an oxidation number of 0 (e.g. H2)
What are the rules involving oxidation numbers for compounds?
- in a neutral compound, the sum of the oxidation numbers is 0
- each atom in a compound has an oxidation number (and the sum of all of those is 0)
What are the rules involving oxidation numbers for ions?
- a simple monatomic ion has an oxidation number the same as its charge
- in molecular ions, the sum of the oxidation numbers is the same as the overall charge
Oxidation numbers you need to know:
- oxygen is almost always -2
[except in peroxides (-1), and when bonded to F (+2)] - hydrogen is almost always +1
[except in metal hydrides (-1)] - fluorine is always -1
- group 1 elements are always +1
- group 2 elements are always +2
How are Roman numerals used to indicate the magnitude of oxidation number of an element?
the roman numeral stands for the oxidation number
e.g. iron (II) sulfate - iron has an oxidation number of +2, but in iron (III) sulfate - iron has an oxidation number of +3
What is oxidation and reduction in terms of electron transfer?
oxidation is loss of e-
reduction is gain of e-
OILRIG
What is oxidation and reduction in terms of changes in oxidation number?
oxidation = oxidation number increases
reduction = oxidation number decreases
Describe the redox reactions of metals with acids to form salts (including full equations):
- metal + acid → salt + hydrogen
(e.g. Mg + 2HCl → Mg(Cl)2 + H2) - the metal is always oxidised (loses e- to form positive metal ions in salts)
- the hydrogen ions (in the acid) are reduced (gain e- to form hydrogen molecules)
- in terms of oxidation numbers:
e.g. Mg + 2 HCl -> MgCl2 + H2
-the oxidation number of Mg increases from 0 to +2 so Mg is oxidised
-the oxidation number of H decreases from +1 to 0 so H is reduced
What is an oxidising agent?
it oxidises another species, and it itself is reduced
What is a reducing agent?
it reduces another species, and it itself is oxidised
How do you combine half equations?
balance the e- (same number of e- on both sides) to cancel them out
How do you write redox half equations?
- balance the key elements
- balance the oxygens with H2Os
- balance the H2Os with H+ ions
- the balance the elections
