Module 2 (chapter 4) - acid and redox Flashcards
acid
a species that donates a proton (H+) when dissolved in water as it dissociates into its components
-they give PHs of less than 7
three common inorganic acids
- sulphuric acid (H2SO4)
- hydrochloric acid (HCl)
- Nitric acid (HNO3)
- hydrogen is always at the start of inorganic acids
three common organic acids
- ethanoic acid (CH3COOH) vinegar
- methanoic acid (HCOOH) in insert bites
- citric acid (C6H8O4) in citrus fruits
what is a strong acid?
-completely dissociates when dissolved in water or aqueous solution
-this meanest releases all its H+ atoms
(HCL –> H+ + Cl -)
what is a weak acid?
-only partially dissociates in water or aqueous solution
-only releases a small proportion of its available hydrogen atoms
(CH3COOH H+ + CH3COO-) the equilibrium sign indicates that the forward reaction is incomplete
what is important to note about compounds that contain hydrogen?
- they’re not all acidic
- e.g. each molecule of ethnic acid contains four hydrogen atoms but only the hydrogen atom on the COOH group is released as H+
bases
a species that is a H+ (proton) accepter
- a base neutralises an acid to form a salt
- common bases are metal oxides and hydroxides
- ammonia is also classified as a base as it has a lone pair
- alkalis are a type of base
alkalis
a type of base that dissolves in water to form hydroxide (OH-) ions
- a chemical which gives a solution above 7 when dissolved in water
- 3 common alkalis are ammonia, sodium and potassium hydroxide
- can sometimes be more corrosive and ore dangerous than acids
ammonia
- a gas that dissolves in water to form a weak alkaline solution (NH3 + H2O NH4+ + OH-)
- ammonia is a weak base because only a small proportion of the ammonia dissolves
what is a neutralisation reaction?
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 is the neutralisation of acids like?
-when neutralised by a metal oxide or hydroxide it forms salt and water only
acid + alkali – salt and water
-when neutralised with carbonate the products are salt, water and carbon dioxide
what is a titration?
a technique used to accurately measure the volume of one solution that reacts exactly with another
-They’re often used when finding the concentrating of a solution, identification of unknown chemicals and finding the purity of a substance
how do you prepare a standard solution?
use a volumetric flask
-weight the solid accurately first
-solid is dissolved in a beaker of distilled water
-transfer solution to a volumetric flask
-carefully fill to the graduation line by adding distilled water drop-wise. try to view the meniscus at eye level
-slowly invert the flask several times to mix the solution thoroughly
to increase accuracy:
- 2 or more decimal place balance, rinse beaker and transfer washings to flask, invert with stopper
what are the uncertainties in pipettes and burettes
- a 10cm3 pipette (+/- 0.04cm3)
- a 25cm3 pipette (+/- 0.06cm3)
- a 50cm3 pipette (+/- 0.1cm3)
- a burette reading is recoded to the nearest half division with the bottom of the meniscus on the mark of between two marks (each reading is measured to the nearest +/- 0.05cm3)
working out the mean titre
-repeat titre until two are concordant of each other and rejecting other inaccurate readings
what is oxidation?
- loss of electrons
- gain of oxygen
- loss of hydrogen
- rise in oxidation number/increase in oxidation state
what is reduction?
- gain of electrons
- loss of oxygen
- gain of hydrogen
- decrease in oxidation number/decrease in oxidation state
oxidation number
a measure of the number of electrons that an atom uses to bond with atoms of another element
- sum of oxidation numbers equals charge
- used to see what has been oxidised and what reduced
oxidation number rules of elements
-always zero for elements or things in tier elemental form (P4, S8)
oxidation number rules for compounds and ions
- each atom in a compound has an oxidation number
- an oxidation number is a sign placed before the number
combined oxygen
-2
combined hydrogen
+1
simple ion
charge on ion
combined halogens and fluorine
-1
peroxides
-1
key exceptions and points for oxidation numbers
- when bonded to metal hydrides, hydrogen has an oxidation number of -1
- the more electronegative an atom the more negative the oxidation state
- O bonded to F is +2
oxide, ate and ide endings
- ate with oxygen
- ide without oxygen
- oxide- oxygen attached to a non oxygen
NO2- and NO3-
- nitrite, +3
- nitrate, +5
rules for half equations
if electrons on the
- RHS its oxidation
- LHS its reduction
- balance elements and then the charges using electrons in half equations
- to form an ionic equation combine without electron notations and spectator ions
redox reaction
are when both oxidation and reduction both happen simultaneous
reducing agent
a species being oxidised so forcing another species to be reduced
oxidising agent
a species itself which is reduced so forcing the other species to be oxidised
disproportionation reaction
a type of redox where one species one species is both oxidised and reduced at the same time
