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2470883
Acid and Bases
Descrição
Mapa Mental sobre Acid and Bases, criado por Amy Holden em 10-04-2015.
Sem etiquetas
aqa
a level chemistry
acid and bases
chapter 3
Mapa Mental por
Amy Holden
, atualizado more than 1 year ago
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Criado por
Amy Holden
mais de 9 anos atrás
65
3
0
Resumo de Recurso
Acid and Bases
Acid-base theories
Lewis
Acid - electron pair acceptor
Base - electron pair donor
Bronsted-Lowry
Acid - proton donor
Base - proton acceptor
Conjugate systems
Acids are related to bases
ACID <=> PROTON + CONJUGATE BASE
Bases are related to acids
BASE + PROTON <=> CONJUGATE ACID
For an acid to behave as an acid, it must have a base present to accept a proton
acid + base <=> conjugate base + conjugate acid
HA + B <=> BH+ + A-
pH = -log10[H+]
The smaller the pH, the greater the conc. of H+
pOH = -log10[OH-]
Kw = [H+][OH-]
water is weakly dissociated
Weak acids and bases
weak acids and weak bases dissociate only in aqueous solution
Ka = ([H+][A-]) / [HA]
Ka is the dissociation constant for a weak acid
Ka = [H+]2 / [HA]
The weaker the acid..
the less it dissociates
the fewer ions you get
the smaller Ka
pKa
very weak acids have very small Ka values
Its is easier to compare the strength as pKa
pKa = -log10 (Ka)
species that can act as an acid or base are amphoteric
Strong acids
a strong acid is one which dissociates completely in water into H+ and A-
Examples
HCl
HNO3
H2SO4
Strong acids do not dissociate fully at high concentrations
There is not enough water
diluting the acid tenfold causes the pH to increase by one unit
Titrations
Curves
Indicators
Buffers
A solution that resists change of pH when small amounts of acid or base are added or on dilution
Acidic buffers
They are made from a mixture of a weak acid and a soluble salt of that acid
It will maintain a pH of below 7
The weak acid component is to act as a source of HA to remove any added OH-
HA + OH- --> A- + H2O
The salt component is to act as a source of A- to remove any added H+
A- + H+ --> HA
It is possible to saturate a buffer
Basic buffers
It will maintain a pH of above 7
They are made from a mixture of a weak base and a soluble salt of that base
Aqueous ammonia and ammonium chloride acts as a bsic buffer
NH3 + H+ --> NH4+
NH4+ + OH- --> NH3 + H2O
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