IONS in AQUEOUS SOLUTIONS by MikeJenny

VIEWS: 253 PAGES: 34

									IONS
in AQUEOUS
SOLUTIONS
I. Ionic Salts

  A. Dissociation: separation of ions that occur
   when an ionic compound dissolves
• refers to ionic salts ONLY
• the salt separates in solution (usually water) to
  form cations and anions
• ex. ionic equation: NaCl(aq) ↔ Na+ + Cl-

  B. Forms electrolytes (ions), which enables the
  solution to conduct electricity
                Examples - Dissociation
Ex: LiCl (s)    Li +(aq) + Cl -   (aq)   What is the total number of
                                          moles of ions produced? _____

Ex. Ca(OH)2 (s)         +                What is the total number of
                                          moles of ions produced? _____



Ex. Al2(SO4)3 (s)       +                What is the total number of
                                          moles of ions produced? _____
II. Covalent Molecules

A. Ionization: the formation of ions from
  molecular solutes by action of the solvent
  – No ions existed before contact with the solvent
  – Refers to covalent molecules ONLY
  – Acids are good examples!
         Examples - Ionization
• Ex: HCl (aq)  H+ (aq) + Cl-   (aq)




• Ex: H3PO4 (aq)         +
B. Hydronium Ion   (H3O+)

   H2O + HCl ↔      H3O+ + Cl-
III. Net Ionic Equations:
• Includes only those substances that undergo a
   chemical change in the reaction in an aqueous
   solution
• Spectator Ions: ions that do not chemically
   change….not written in the net ionic equation
• Ex. For…..
• Cd (NO3)2 (aq) + (NH4)2S (aq) →



  Net Ionic Eq:

  Spectator Ions:
•Ex. AgC2H3O2 (aq) + CaCl2 (aq) →

Net Ionic Eq:

Spectator Ions:
•Ex.   NaOH (aq) + Fe(ClO3)3 (aq) →


Net Ionic Eq:

Spectator Ions:
IV. Molecular electrolytes:
• Strong Electrolytes:
   – any solute that is present entirely as hydrated ions
   – A high degree of ionization or dissociation. All or almost all of the
     compound forms ions in solution. 100% or close to that of ionization
     or dissociation.
       ex.      HCl, strong acids, ionic salts
                Strong acids include: HBr, HCl, HI
                Strong bases include: Gp IA and IIA hydroxides, except Be
• Weak Electrolytes:
   – a solute that yields a relatively low concentration of ions in aqueous
     solution…partial ionization
   – A low degree of ionization or dissociation.
       ex.      “weak” acids
                Weak acid =   HF, acetic acid
                Weak base =   NH4OH
The ammeter measures the flow of electrons (current)
through the circuit.
•If the ammeter measures a current, and the bulb glows,
then the solution conducts.
•If the ammeter fails to measure a current, and the bulb
does not glow, the solution is non-conducting.
V. Properties of electrolytic solutions:

A. Conductivity: the magnitude of the current
  depends on the solute ion concentration
  …Pure water is a poor conductor, but it does
  conduct some due to the self-ionization of
  water…making hydronium

B. Colligative Properties: influence of electrolytes
   on the BP and FP
   …depend on concentration of solute (or ions, if
   it is an electrolytic solution)
   VI. Colligative       Properties
 Properties that depend on the
  concentration of solute particles but
  not on their identity

 4 colligative properties:

Osmotic Pressure
Vapor Pressure Lowering
Freezing Point Depression (our focus)
Boiling Point Elevation (our focus)
The vapor pressure of a pure solvent is higher than a solution.
A. Freezing Point Depression
• Adding a solute lowers the FP of the solvent
• The “new” FP is in between the solute and
  solvent FPs
• Directly proportional to molal concentration
• Kf…molal FP constant
• Kf…for water….   -1.86 °C/m
B. Boiling Point Elevation
• Adding a solute raises the BP of the solvent
• Kb…molal BP constant

• Kb…for water…     0.51 °C/m
C. Math:
• ΔT = Kf m (#moles)

• ΔT = Kb m(# moles)

      where K is in °C/m

     expanded…ΔT = K• molsolute
                  kgsolvent
Non-Electrolytic Solutions:
Sugars and other hydrocarbons are nonpolar covalent and do not
form ions in solution These substances are termed non-
electrolytes. Sugars are not salts, acids or bases. Sugars are
organic molecular compounds and do not dissociate or ionize.




Ex. 1 What is the FPD of a 2.55 m
glucose aqueous solution?
Ex. 2 What is the
concentration (molality) of
a glucose solution that has
a -3.25ºC FPD?
Ex. 3 What is the BPE
of a glucose solution with
1.25 mol of glucose
dissolved in 0.500 kg of
water?
Ex. 4 What mass of glucose
(C6H12O6) would be needed
to cause a FPD of -1.14 ºC
in 750. g of water?
Ex. 5 What is the molar mass
of a non-electrolytic
substance if 155 g of the
substance dissolved in 0.855
kg of water causes a 2.00 ºC
BPE?
Electrolytic Solutions:

Ex. 6 What is the FPD of a 3.1 m
NaCl aqueous solution? What is
the new FP?
Ex. 7 How many moles of
NaCl are needed to lower
the FP of 3.6 kg of water
by 5.6 ºC?
Ex. 8 What mass of KCl is
needed to change the BP of
4.5 kg of water to 104.2 ºC?

								
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