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)