Download constructing relative reactivity tables

CONSTRUCTING RELATIVE
REACTIVITY TABLES
• we will examine the observations made
when a group of elements and their ions
are mixed together.
• We will then arrange these elements into a
table showing relative reactivity.
• This could be in terms of the easiest to the
most difficult to be oxidized or reduced; or
in terms of the best/worst oxidizing agent
or reducing agent
SAMPLE PROBLEM 1
•
Four elements, A, B, C, and D, form
diatomic molecules and ions with a 1charge.
1. B- + C2 → C- + B2
2. A- + C2 → No Reaction
3. D- + B2 → B- + D2
a) Write the equation for each reduction half reaction.
b) Arrange the equations in a relative reduction potential
table with the easiest to reduce at the top and the
hardest to reduce at the bottom.
c) Write the equation for each oxidation half reaction.
d) Arrange the equations in a relative oxidation potential
table with the easiest to oxidize at the top and the
hardest to oxidize at the bottom.
e) Which is the best oxidizing agent? Which is the best
reducing agent?
SAMPLE ANSWER 1
a) The reduction half reactions are:
C2 + 2e- → 2CB2+ 2e- → 2BA2+ 2e- → 2AD2+ 2e- → 2D-
b) Equation (2) indicates no reaction. However,
this means no forward reaction. The reverse
reaction will take place:
C- + A2 → A- + C2
• C2 reacts with B-, ∴ C2 is above B2 in table
• A2 reacts with C-, ∴ A2 is above C2
• B2 reacts with D-, ∴ B2 is above D2
• This works out to A2 is above C2 , C2 is above B2
, and B2 is above D2 .
Table for (b)
• Reactivity table for reduction half
reactions, easiest to reduce top, hardest
on bottom
• A2 + 2e- → 2A• C2 + 2e- → 2C• B2 + 2e- → 2B• D2 + 2e- → 2D-
c) The oxidation half reactions are:
• 2A- → A2 + 2e• 2C- → C2 + 2e• 2B- → B2 + 2e• 2D- → D2 + 2e
d)
• B- reacts with C2, ∴ B- is above C
• C- reacts with A2, ∴ C- is above A
• D-reacts with B2, ∴ D- is above B
So, D-is above B-, B- is above C-, and C- is above A-.
• 2D- → D2 + 2e• 2B- → B2 + 2e• 2C- → C2 + 2e• 2A- → A2 + 2ee) The best oxidizing agent is the one that is easiest to
reduce, A2. The best reducing agent is the one that is
easiest to oxidize, D-.
SAMPLE PROBLEM 2
• Four metals, Ca, Mn, Pb, and Mg and their
ions with a 2+ charges were involved in
experiments that gave the following
results:
1. Mg + Mn 2+ → Mg 2+ + Mn
2. Mg 2+ + Ca → Mg + Ca 2+
3. Pb + Mn 2+ → No Reaction
a) Write the equation for each reduction half
reaction.
b) Arrange the equations in a relative
reduction potential table with the easiest to
reduce at the top and the hardest to
reduce at the bottom.
c) Write the equation for each oxidation half
reaction.
d) Arrange the equations in a relative
oxidation potential table with the easiest to
oxidize at the top and the hardest to
oxidize at the bottom.
Practice 3
• Experiments were performed with 4 metals
and solutions of their positive ions: Zn/Zn2+
, Fe/Fe 2+ ,Ag/Ag +, Cu/Cu 2+ .The
following observations were made:
i) Fe 2+ + Zn → Fe + Zn 2+
ii) Fe 2+ + Cu → No Reaction
iii) 2Ag + + Cu → 2Ag + Cu 2+
• Answer parts a to e, like previous sample
problems.