09107 Lecture Notes - Ionic Bonding, Lead, Silver Iodide

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Published on 10 Sep 2013
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Course
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September 6, 2013
Honors Chemistry Lecture 5
Today: Qualitative analysis using precipitation in water
For our purposes, when dealing with precipitates we will assume the following:
Our solvent is water
We are dealing with a neutral pH of 7
We will not really discuss sulfides (S2-) or oxides (O2-)
Ionic bonding in solids:
Coulomb’s law: E = ~ (q1 q2) / r (where E = energy, q = charge of ion, ~ = constants we arent worried
about, r = distance between two ions)
Therefore O2- and S2- will form very stable solids
Therefore SO42- is soluble because its so big; its size causes Coulombs law to
counteract the charge
General Solubility Rules:
Group 1 alkali metals are always soluble
Compounds containing NO3 are always soluble
Compounds containing NH4+ are soluble
Compounds containing OH- are insoluble (except with Group I alkali metals and Ba2+, Ca2+, Sr2+)
Compounds containing S2- are insoluble (except with Group I alkali and Group II alkaline metals)
Compounds containing SO3-, CO3-, CrO4-, and PO43- are insoluble (except for those with NH4+ or
Group I alkali metals)
Besides the general solubility rules, you can also remember solubility rules for certain groups of ions
(i.e., the silver group, the copper-arsenic group, the aluminum-nickel group, and the barium-magnesium
group)
The Silver Group:
The silver group is made up of silver (I) [Ag+], mercury (I) [Hg+], and lead (II) [Pb2+]
All of these form insoluble chlorides
In general, chloride salts are soluble
Tend to form white precipitates (ppt)
Remember that Hg+ is a paramagnetic species so it cannot stay in this form. Instead, it becomes
Hg22+ [Hg+ Hg22+]
Side note: Pb4+ is always insoluble
Some Compounds with Ag+ and their Solubility
Soluble (all colorless)
Insoluble (form colored ppt)
AgNO3, AgF, Ag2SO4 (slightly soluble),
Ag(CN)2 (basic solution)
AgCl (white), AgBr (yellow), AgI (yellow), Ag2O
(brown), Ag2CO3 (yellow), Ag2CrO4 (dark red)
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