Download Intro to Soln Stoich

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Solutions where water is the solvent
◦ Chemical is dissolved in water
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Water is the “universal solvent”
◦ O-H bonds are covalent, e- not shared equally
◦ Oxygen has a slight negative, hydrogen slight
positive
 Polar molecule
 Oxygen has a strong attraction to cations, hydrogen to
anions
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Molecules “fall apart” or dissolve when
surrounded by water molecules
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Once dissolved, ions exist separately
Solution contains both cation and anion
Solubility (dissolve-ability) of substances
varies greatly
Nonpolar molecules (fats, oils) do not
dissolve in water
“Like dissolves like”
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Solutions with a large number of ions present
in solution are excellent conductors of
electricity
◦ Completely ionized
◦ Strong electrolyte
 Strong acids (HCl, H2SO4), strong bases (NaOH, KOH),
salts (NaCl, KBr)
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Weak conductors have only a few ions present
in solution
◦ Partially ionized
◦ Weak electrolyte
 Weak acids (HF, HC2H3O2), weak bases (NH3)
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Show the amount of ionization occurring
◦ Example: Magnesium chloride dissolving in water
MgCl2(s)

Mg2+(aq) + 2 Cl-(aq)
◦ Positive ends of water surround the chlorine,
negative ends surround magnesium
 Ions are hydrated
 Strong electrolyte
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Acetic acid in water
HC2H3O2(aq)     H+(aq) + C2H3O2-(aq)
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Partially dissociates
◦ Weak electrolyte
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Ethanol in water
C2H5OH(aq)
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No ionization
No ionization
◦ No ions in solution
◦ Non electrolyte – sugars, alcohols
Molarity (M) =
mol of solute
L of solution
3 M KOH: 3 mol of KOH
1 L of solution
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Concentration of ions in solution can be
calculated
MgCl2(s)
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Mg2+(aq) + 2 Cl-(aq)
If MgCl2 is 0.2 M, what is concentration of Mg2+?
Of Cl-?
Concentration of Mg2+is 0.2 M and Cl- is 0.4 M
◦ 1:1 ratio of MgCl2 : Mg2+
◦ 1:2 ratio of MgCl2 : Cl-
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Square brackets are used to denote concentration
[MgCl2] = 0.2 M
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Calculate the number of moles of Cl- in
1.75 L of 1.0 x 10-3 M ZnCl2
water
ZnCl2 
Zn+ + 2 Cl-
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Solutions are often more concentrated than
you need.
M1V1 = M2V2
What volume of 16 M sulfuric acid must be
used to prepare 1.0 L of a 0.20 M H2SO4
solution ?
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Occurs when certain cations and anions join
to form insoluble compounds
◦ Compounds don’t dissolve in water
◦ Form (insoluble) solids – precipitates
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Ionic compound bonded so strongly, water
can’t pull it apart
We need to know solubility rules!
◦ Sadly, lots of memorization 
◦ Thankfully, your teacher gave you a handy chart 
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An “easy” way to think about them
Always Soluble
Except With
NH4+, NO3-, ClO3-, ClO4-, C2H3O2No exceptions!
and IA metals
Cl-, Br-, I-
Ag+, Hg2+ and Pb2+
SO42-
Ca2+, Sr2+ Ba2+, Ag+, Hg2+ and
Pb2+
F-
IIA Metals
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Based on solubility rules, we can predict what
will happen in reactions
Will a precipitate form when solutions of
silver nitrate and lithium bromide are mixed?
AgNO3(aq) + LiBr(aq)  AgBr(?) + LiNO3(?)
Is Br- soluble with Ag+?
Is NO3- soluble with Li+?
AgNO3(aq) + LiBr(aq)  AgBr(s) + LiNO3(aq)
◦ Nitrate – ALWAYS, IA – ALWAYS
◦ Br- - sometimes, but not with Ag+
 If
there is no precipitate, the
reaction does not occur
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Ions would all still be in solution
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Ions switch partners
Mix together solutions of MgCl2 and AgNO3
MgCl2(aq) + 2 AgNO3(aq)  Mg(NO3)2(?) + 2 AgCl(?)
Is Mg(NO3)2 soluble? Is AgCl?
MgCl2(aq) + 2 AgNO3(aq)  Mg(NO3)2(aq) + 2 AgCl(s)
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Can calculate the mass or concentration of
ions/precipitate is formed.
AgNO3(aq) + NaCl(aq)  AgCl(s) + NaNO3(aq)
If 0.275 L of .100 M AgNO3 is mixed with
0.135 L of 1.00 M NaCl, how many grams of
AgCl would be formed?
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Find moles of each reactant to find limiting
reactant
Find out how many moles of solid AgCl
forms
Convert to grams