Page 354 - General Knowledge

GENERAL KNOWLEDGE 2019

 Aqueous solutions of salts that are products of strong acidic-weak base reactions are acidic.
+
 The Cations react with water and increases [H 3O ] in solutions.
 Salts of Weak Acid-Weak Base Reactions: such as NH 4C 2H 3O 2, NH 4CN, NH 4NO 2, etc.

 Solutions of salts that are products of weak acid-weak base reactions can be neutral, acidic,
or basic, depending on the relative magnitude of the K a of the weak acid and the K b of the
weak base.

5. ELECTROCHEMISTRY
A branch of chemistry that deals with the exploitation of spontaneous oxidation-reduction
reactions to obtain electrical energy and the use of electrical energy to drive nonspontaneous
reactions important in the industrial extraction of certain elements.
Electrode potentials and their measurements
 One of the most common redox reactions is that which occurs when metals are immersed
into solutions of dissimilar metal ions is the single replacement reaction.
 In other cases, mixing ions (in the presence of acid) leads to more complicated redox
reactions (recall the iodometric titration in the fall).
 Regardless of complexity, some metals and ions are more easily reduced than others.
 This difference in affinity for electrons drives chemical reactions.
 The ease of oxidation, or the more accepted ease of reduction, is known as the Standard
Electrode Potential.
 It is measured in volts which have the units, Joules/coulomb.
 It is more a theoretical idea than anything functional. It is a half-cell represents the "half
reaction" from balancing redox reactions last fall and "half" of a reaction cannot occur.
 Each metal will have a unique equilibrium with its ions that will result in a slight positive or
negative charge build-up on the electrode.
 This tendency cannot be measured directly but can be measured by connecting different
half-cells to each other.
-
-
 Electrons will flow from the electrode of higher e density to the electrode of lower e density
(akin to electrons "diffusing").
 To measure the difference in potential we connect two half-cells by joining the electrodes
with a wire and the cells to each other with a salt bridge to maintain electro-neutrality.
 As ions related to the electrode enter or leave the solution, spectator ions in the salt bridge
migrate into the solutions to maintain charge balance.
 The two half-cells, external electron circuit and the salt bridge is an Electrochemical Cell.
 The voltage is the potential difference between the two half-cells and is called the
electromotive force (emf) or the cell potential.

Galvanic and Electrolytic Cells
2+
-
 At anode Cd is oxidized, Cd goes into solution, balanced by NO 3 coming from salt bridge
2+
-
 At cathode, Ni is reduced, comes out of solution as Ni, balanced by NO 3 going into the
bridge
-
 Negative charge as NO 3 flows through bridge from cathode (Ni) to anode (Cd)
-
 Negative charge as e flows through wire from anode (Cd) to cathode (Ni)
2+
2+
+
 Conversely, Na moves through bridge to Ni side (Ni consumed) from Cd side (Cd
produced).

350 | P a g e shop.ssbcrack.com