acids, bases and ions in aqueous solution
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Chapter 7. Acids, bases and ions in aqueous solution. 7.1 Introduction. Liquid water is approximately 55 molar H 2 O,. 7.2 Properties of water. structure. Part of the structure of ordinary ice; it consists of a 3-dimensional network of hydrogen-bonded H 2 O molecules. - PowerPoint PPT PresentationTRANSCRIPT
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Acids, bases and ions in aqueous solution
Chapter 7
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7.1 Introduction
Liquid water is approximately 55 molar H2O,
7.2 Properties of water
structure
Part of the structure of ordinary ice; it consists of a 3-dimensional network of hydrogen-bonded H2O molecules.
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The variation in the value of the density of water between 283 and 373 K.
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The self-ionization of water
If a pure liquid partially dissociates into ions, it is self ionizing.If a pure liquid partially dissociates into ions, it is self ionizing.
Water as a Brønsted acid or base
A Brønsted acid can act as a proton donor, and a Brønstedbase can function as a proton acceptor.
A Brønsted acid can act as a proton donor, and a Brønstedbase can function as a proton acceptor.
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Brønsted base
Brønsted acid
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Activity
When the concentration of a solute is greater than about0.1 mol/dm3, interactions between the solute molecules orions are significant, and the effective and real concentrationsare no longer equal.
The relative activity, ai, of a component i is dimensionless
i is the activity coefficient of the solute, and mi is the molality
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7.4 Some Brønsted acids and bases
Carboxylic acids: examples of mono-, di- and polybasic acids
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Inorganic acids
Each of the hydrogen halides is monobasic and for X = Cl, Br and I, the equilibrium lies far to the right-hand side, making these strong acids
Hydrogen fluoride, on the other hand, is a weak acid (pKa = 3.45).
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oxoacid
Examples of oxoacids include hypochlorous acid (HOCl),perchloric acid (HClO4), nitric acid (HNO3), sulfuric acid(H2SO4) and phosphoric acid (H3PO4).
oxoacids may be mono-, di- or polybasic; not all the hydrogen atoms in an oxoacid are necessarily
ionizable.
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Dr. Said M. El-Kurdi 11
It is not possible to isolate pure H2SO3 - sulfurous acid
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phosphinic acid has the formula H3PO2, is monobasic
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Inorganic bases: hydroxides
Many inorganic bases are hydroxides, and the term alkali iscommonly used.The group 1 hydroxides NaOH, KOH, RbOH and CsOH are strong bases, being essentially fully ionized in aqueous solution; LiOH is weaker (pKb = 0.2).
Inorganic bases: nitrogen bases
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7.5 The energetics of acid dissociation in aqueous solution
Hydrogen halides
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H2S, H2Se and H2Te
the explanation of the trend in values is not simplethe decrease in the XH bond strength with the increasing atomic number of X plays an important role
as group 16 is descended and X becomes more metallic, its hydride becomes more acidic.
as group 16 is descended and X becomes more metallic, its hydride becomes more acidic.
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7.6 Trends within a series of oxoacidsEOn(OH)m
empirical methods for estimating Ka
Bell’s ruleWhich relates the first acid dissociation constant to the number of ‘hydrogen-free’ O atoms in an acid of formula EOn(OH)m.
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The increase in acid strength with increase in the number of O atoms attached to atom E is generally attributed to the greater possibility in the conjugate base of delocalization of negative charge onto the O atoms.
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7.7 Aquated cations: formation andacidic properties
When a metal salt dissolves in water, the cation and anion are hydrated.
ion–dipole interaction
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Hexaaqua ion
the first hydration shell
each H2O molecule acts as a Lewis basewhile the metal ion functions as a Lewis acid.
the MO interaction is essentially covalent
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7.8 Amphoteric oxides and hydroxides
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Periodic trends in amphoteric properties
some elements that lie next to the line ‘diagonal line’ (e.g. Si) are semi-metals
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Be(OH)2 and BeO are amphoteric
Al2O3, Ga2O3, In2O3, GeO, GeO2, SnO, SnO2, PbO, PbO2, As2O3, Sb2O3 and Bi2O3 are amphoteric.
7.9 Solubilities of ionic salts
Solubility and saturated solutions
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The temperature-dependence of the solubilities in water
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Sparingly soluble salts and solubility products
The energetics of the dissolution of an ionic salt: solGo
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7.11 Coordination complexes: anintroduction
Definitions and terminology
The word ligand is derived from the Latin verb ‘ligare’ meaning ‘to bind’.
In a coordination complex, a central atom or ion is coordinated by one or more molecules or ions (ligands) which act as Lewis bases, forming coordinate bonds with the central atom or ion; the latter acts as a Lewis acid.
In a coordination complex, a central atom or ion is coordinated by one or more molecules or ions (ligands) which act as Lewis bases, forming coordinate bonds with the central atom or ion; the latter acts as a Lewis acid.
Atoms in the ligands that are directly bonded to the central atom or ion are donor atoms.
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In a complex:a line is used to denote the interaction between an anionic ligand and the acceptor;an arrow is used to show the donation of an electron pair from a neutral ligand to an acceptor.
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When a Lewis base donates a pair of electrons to a Lewis acid, a coordinate bond is formed and the resulting species is an adduct. The centred dot in, for example, H3BTHF indicates the formation of an adduct.
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Investigating coordination complexformation
7.12 Stability constants of coordination complexes
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Stepwise stability constants for the formation of[Al(OH2)6xFx](3x)+ (x = 1–6).
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For ions of similar size, the stability of a complex with a specified ligand increases substantially as the ionic charge increases, e.g. Li+ < Mg2+ < Al3+.
For ions of similar size, the stability of a complex with a specified ligand increases substantially as the ionic charge increases, e.g. Li+ < Mg2+ < Al3+.
The stabilities of complexes of the non-d-block metal ions of a given charge normally decrease with increasing cation size .Thus, for a complex with a given ligand, L, the order of stability is Ca2+ > Sr2+ > Ba2+.
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Hard and soft metal centres and ligands
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The principle of hard and soft acids and bases (HSAB)
hard, metal ions and ligands containing particular donor atoms exhibit trends in stabilities as follows:
soft, metal ions and ligands containing these donor atoms are:
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Pearson’s classification of hard and soft acids comes from a consideration of a series of donor atoms placed in order of electronegativity:
A hard acid is one that forms the most stable complexes with ligands containing donor atoms from the left-hand end of the series. The reverse is true for a soft acid.
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Polarizability
The polarizability, of an atom is its ability to be distorted by an electric field (such as that of a neighboring ion)
Small, highly charged cations have polarizing ability. Large, highly charged anions are easily polarized. Cations that do not have a noble-gas electron configuration
are easily polarized.
Fajan’s rules
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Which would be the more polarizable, an F ion or an I ion?
Which would be more polarizing, Na+ or Cs+?