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Chapter 4
Types of Chemical Reactions and Solution Stoichiometry
Water, the Common Solvent
Oxygen has a greater attraction for electrons than does hydrogen
The oxygen atom gains a slight excess of negative charge (partial negative charge ), and the hydrogen atoms become slightly positive (partial positive charge ).
Water is said to be a polar molecule.
An Ionic Solid Dissolving in Water
The positive ends of water molecules are attracted to the negatively charge anions.
The negative ends are attracted to the positively charge cations.
This process is called hydration.
Polar water molecules
Ethanol molecule in Water
Strong Electrolytes
Soluble salts: NaCl, KCl, NH4Cl
Strong acids: HCl, HNO3, H2SO4
Strong bases: NaOH, KOH
HCI container
NaOH container
Weak Electrolytes
Weak acid: acetic acid
HC2H3O2(aq) → H+(aq)+C2H3O2
-(aq)
Weak base: ammonia dissolving in water
NH3(aq)+H2O(l) →NH4+
(aq) +OH-
(aq)
Acetic acid
NH3 in water
Standard Solution A standard solution is a solution whose concen
tration is accurately known. Primary Standard : A primary standard is a hi
ghly purified compound that serves as a reference material in all volumetric and mass titrimetric methods.
Secondary Standard: A second standard is a solution of known concentration by titration with a solution of primary standard.
Preparing Standard Acid Solutions Hydrochloric acid is widely used for titration of
bases. Dilute solutions of HCl are stable indefinitely and
do not cause troublesome precipitation reactions with most cations.
0.1 M solutions of HCl can be boiled for as long as one hour without loss acid.
0.5 M solutions of HCl can be boiled for at least 10 min without significant loss.
Solutions of perchloric acid and sulfuric acid are also stable and are useful for titration where chloride ion interferes by forming precipitates.
Solutions of nitric acid are seldom encountered because of their oxidizing properies.
Requirements for a Primary Standard
High purity Atmospheric stability Absence of hydrate water - composition of t
he solid does not change with relative humidity
Ready availability at modest cost Reasonable solubility in the titration medium Reasonably large molar mass - the relative e
rror associated with weighing
Several Excellent Primary Standards
1. Potassium Hydrogen Phthalate KHC8H4O4 (KHP)
2. Benzoic Acid: its solubility in water is limited, this reagent is ordinarily dissolved in ethanol prior to dilution water.
3. Potassium Hydrogen Iodate KH(IO3)2: is an excellent primary standard with a high molecular mass per mole of protons.
Preparation of standard solutionor stock solution
Types of Chemical Reactions
Precipitation reactions
Acid-base reactions
Oxidation-reduction reactions
Precipitation Reactions
K2CrO4 /Ba(NO3)2
Reaction of KCI/AgNO3
Ag/Ba/Fe precipitation