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Chapter 5

CHM101H1 Chapter Notes - Chapter 5: Silver Iodide, Lead, Sulfuric Acid


Department
Chemistry
Course Code
CHM101H1
Professor
x
Chapter
5

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Chemistry Chapter Five
The Nature of Aqueous Solutions
Reactions in aqueous (water)solution are important because: (1) water is
inexpensive and is able to dissolve a vast number of substances; (2) in such
solutions, many substances are dissociated into ions which can participate chemical
reactions; and (3) these solutions are found everywhere, from seawater to living
systems.
Unlike metallic conductors in which electrons carry the electric charge, the electricity
conducted in aqueous solutions is carried by the ions. When a solute dissociates into
ions in an aqueous solution and becomes and electric conductor, it is known as an
electrolyte. ***Pure water contains so few ions that it does not conduct an electric
current. *** Based on how well a solution conducts electricity, we can deduce the
strength of the presence of ions. We can label a solute as a non-electrolyte, strong
electrolyte, or weak electrolyte. A non-electrolyte is a substance that is not ionized
and does not conduct electric current (e.g. the lamp fails to light up). Therefore, there
are no ions or extremely low concentration of ions. A strong electrolyte is a
substance that is essentially completely ionized in aqueous solution, and the solution
is a good electrical conductor (e.g. the lamp lights up brightly) and thus, has a
high concentration of ions. A weak electrolyte is partially ionized in aqueous
solution and the solution is only a fair conductor of electricity, thus, the concentration
o f ions in the solution is low (e.g. the lamp lights up only dimly). When determining if
a solution is more likely to be a strong electrolyte, weak electrolyte or non-electrolyte,
it is best to remember this generalization:
Essentially all soluble ionic compounds and only a relatively few molecular
compounds are strong electrolytes.
Most molecular compounds are either non-electrolytes or weak electrolytes.
Some examples of a strong electrolyte are: HCl, NaOH and KBr. Some examples of a
weak electrolyte are: HF, CH3COOH. Some examples of non-electrolytes are: H2O and
CH3OH.
If a solution contains strong electrolytes, the equation is written with the arrow of the
reaction going in one direction, usually right. This indicates that the ionization in
water is complete.
MgCl2(s) (H20) Mg 2+ (aq) + 2Cl-(aq)
In a situation where the solution is characterized as a weak electrolyte is best
described as a reaction that does not go to completion. In these cases, only a portion
of the solute molecules in the solution are ionized. The double arrows indicate that
the process is reversible. This means that while the forward reaction is taking place,
the reverse action is also occurring and its products are the reactants of the forward
reaction.
HC2H3O2H+ (aq) + C2H3O2- (aq)
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