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An Ionic Compound, CuCl2, in Water
CCR, page 177
How do we know ions are present in aqueous solutions?
The solutions conduct electricity!
They are called ELECTROLYTES
HCl, CuCl2, and NaCl are strong electrolytes. They dissociate completely (or nearly so) into ions.
Aqueous Solutions
Aqueous Solutions
Acetic acid is a weak acid, it ionizes only to a small
extent, so it is a weak electrolyte.
CH3CO2H(aq) <--->
CH3CO2-(aq) + H+(aq)
Acids ---> H+ in water
ACIDS
HCl(aq) ---> H+(aq) + Cl-(aq)
HCl is a strong acid
Other strong acids include:HI, HBr, HNO3, H2SO4, HClO4
Weak acids have H+ as the cation, and are not STRONG acids.
Base ---> OH- in water
BASES
NaOH(aq) ---> Na+(aq) + OH-(aq)
NaOH is a strong base
Other strong bases include:LiOH and KOH
Weak bases have OH- as the anion, and are not STRONG bases.
Ammonia, NH3
An Important Weak Base
Aqueous Solutions
Some compounds dissolve in water but do not conduct electricity. These are molecular compounds, made of molecules, so they do not split into charged particles. They are called nonelectrolytes.
Examples include:sugarethanolethylene glycol
KISS Rules – Keep it Simple Solubility Rules
#1 – Soluble Cations: sodium, potassium, and ammonium are always soluble
#2 – Soluble Anions – nitrate, acetate, chlorate, perchlorate are always soluble
#3 – Soluble Anions – chloride, bromide, iodide are soluble EXCEPT with the SILVER GROUP – silver, mercury and lead
#4 – Soluble Anions – sulfate is soluble EXCEPT with the Silver Group or with strontium or barium
#5 – EVERYTHING ELSE IS INSOLUBLE
Net Ionic Equations
Mg(s) + 2 HCl(aq) --> H2(g) + MgCl2(aq)
We really should write
Mg(s) + 2 H+(aq) + 2 Cl-(aq) --->
H2(g) + Mg2+(aq) + 2 Cl-(aq)The two Cl- ions are SPECTATOR IONS — they do not participate. Could have used NO3
-.
Net Ionic Equations
Mg(s) + 2 HCl(aq) --> H2(g) + MgCl2(aq)
Mg(s) + 2 H+(aq) + 2 Cl-(aq) H2(g) + Mg2+(aq) + 2 Cl-(aq)
We leave the spectator ions out —Mg(s) + 2 H+(aq) ---> H2(g) + Mg2+(aq)
to give the NET IONIC EQUATION
Precipitation Reactions
The “driving force” is the formation of an insoluble compound — a precipitate.
Pb(NO3)2(aq) + 2 KI(aq) 2 KNO3(aq) + PbI2(s)
Net ionic equation
Pb2+(aq) + 2 I-(aq) PbI2(s)