Chapter 4 - Acids and Redox Flashcards
what atom do all acids contain?
hydrogen
what is released when an acid dissolves in water?
hydrogen atoms as protons
what is the difference between a strong acid and a weak acid?
a strong acid releases all of its hydrogen atoms into solution as protons and completely dissociates in aqueous solution
a weak acid releases a small proportion of its hydrogen atoms into solution as protons and partially dissociates in aqueous solution
what does the equilibrium sign indicate in neutralisation?
that the forward reaction is incomplete
are all compounds that contain hydrogen atoms acids?
no
what types of compound are classified as bases?
metal oxides, metal hydroxides, metal carbonates and ammonia
what happens when a base reacts with an acid?
a base neutralises an acid to form a salt
what is an alkali?
a base that dissolves in water releasing hydroxide ions into the solution
what happens during the neutralisation of an acid?
H+ ions react with a base to form a salt and neutral water. the H+ ions from the acid are replaced by metal or ammonium ions from the base
what can an acid be neutralised by to from a salt and water?
a metal oxide or metal hydroxide only
what happens when an acid and alkali react?
acid + alkali -> salt + water
on the ionic scale:
H+ + OH- -> H2O
what happens when an acid is neutralised with carbonates?
acid + carbonate -> salt + water + carbon dioxide
how does sulfuric acid behave as a strong acid and a weak acid?
each molecule in H2SO4 dissociates
- sulfuric acid first behaves as a strong acid:
H2SO4 -> H+ + HSO4 (^-)
- the resulting HSO4 ions only partially dissociate:
HSO4 = H+ + SO4 (^2-)
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
what equipment is used to make up a standard solution?
a volumetric flask
how do you prepare a standard solution?
- weigh the solid accurately
- dissolve the solid in a beaker using distilled water (less than will be needed to fill the volumetric flask)
- transfer the solution to a volumetric flask and rinse the beaker with distilled water into the flask
- fill the flask to the graduation line
- invert the flask several times to mic the solution thoroughly
what are the uncertainties of typical volumetric flasks?
- a 100 cm3 volumetric flask: 0.20cm3
- a 250 cm3 volumetric flask: 0.30cm3
what happens during an acid-base titration?
a solution of an acid is titrated against a solution of a base using a pipette and a burette.
what are the uncertainties of typical pipettes and burettes?
- a 10 cm3 pipette: 0.04 cm3
- a 25 cm3 pipette: 0.06 cm3
- a 50 cm3 burette: 0.10 cm3
how is a burette reading measured in a titration?
to the nearest 0.05 cm3
how do you carry out an acid-base titration?
- add a measured volume of one solution to a conical flask using a pipette
- add the other solution to a burette and record the initial reading
- add drops of indicator to the solution in the conical flask
- run the solution in the burette into the solution in the conical flask, swirling the flask throughout to mix, until the indicator changes colour to mark the end point of the titration
- record the final burette reading and calculate the titre by subtracting the initial from the final reading
- repeat until two titres are concordant and take a mean
what does concordant mean?
within 0.10 cm3
what do you know from the results of a titre?
- the concentration and the reacting volume of one of the solutions
- the reacting volume of the other solution
what is oxidation number?
the number of electrons involved in bonding to a different element
what is the rule for oxidation number for elements?
it is always zero for elements
what is the general rule for oxidation number for compounds and ions?
- each atom in a compound has an oxidation number
- an oxidation number has a sign, which is placed before the number (eg -1)
what is the oxidation number of an O ion?
-2
what is the oxidation number of an H ion?
+1
what is the oxidation number of an F ion?
-1
what is the oxidation number of a Na+, K+ ion?
+1
what is the oxidation number of a Mg2+, Ca2+ ion?
+2
what is the oxidation number of a Cl-, Br-, I- ion?
-1
what is the oxidation number of an H ion in metal hydrides?
-1
what is the oxidation number of an O ion in peroxides?
-1
what is the oxidation number of an O ion bonded to F?
+2
what is the rule for working out oxidation numbers?
sum of the oxidation numbers = total charge
what does a roman numeral symbolise in an element?
the oxidation number of the element
e.g. iron (II) has an oxidation number of +2
what do oxidation and reduction mean (in terms of oxygen)?
oxidation is the addition of oxygen
reduction is the removal of oxygen
what do redox reactions involve?
both reduction and oxidation
what do oxidation and reduction mean (in terms of electrons)?
OIL RIG
oxidation is the loss of electrons
reduction is the gain of electrons
do redox reactions always have to include oxygen?
no
what happens to Fe and Cl when forming FeCL3?
- iron loses electrons and is oxidised: 2Fe -> 2Fe3+ + 6e-
- chlorine gains electrons and is reduced: 3Cl2 + 6e- -> 6Cl-
what do oxidation and reduction mean (in terms of oxidation number)?
- reduction is a decrease in oxidation number
- oxidation is an increase in oxidation number
what happens during redox reactions between acids and metals?
dilute acid + (some) metals -> salt + hydrogen
