Unit 3 Revision

Redox

100

Oxidation involves the _____ of electrons and reduction involves the _____ of electrons

Oxidation involves the loss of electrons and reduction involves the gain of electrons

(remember the acronym OIL RIG!)

200

What is the net reaction and the two half reactions occurring in a hydrogen fuel cell?

O: H₂ + 2OH^- --> 2H₂O + 2e^- (x2 this also okay)

R: O₂ + 2H₂O + 4e^- --> 4OH^-

Overall: 2H₂ + O₂ --> 2H₂O

300

CaCO₃ undergoes thermal decomposition when heated in the following reaction:

CaCO₃ --> CaO + CO₂

Identify the oxidation state of each element in both the reactants and products ($200) and justify if this is a redox reaction ($100)

CaCO₃ --> CaO + CO₂

CaCO₃ - Ca:+2, C:+4, O:-2

CaO - Ca: +2, O:-2

CO₂ - C: +4, O:-2

There is no change in the oxidation states, so it is NOT a redox reaction

400

In a redox reaction in acidified solution, Fe²⁺ is oxidized to Fe³⁺ and MnO₄^- is reduced to Mn²⁺​

​​​What are the two half reactions ($200) and the overall balanced equation ($300)?

O: Fe²⁺ --> Fe³⁺ + e^-

R: 5e^- + 8H⁺ + MnO₄^- --> Mn²⁺ + 4H₂O

Overall: 5Fe²⁺ + 8H⁺ + MnO₄^- --> Mn²⁺ + 4H₂O + 5Fe³⁺

d-block Chemistry

100

In [Cu(H₂O)₆]²⁺, what kind of bond exists between the metal and the ligand? Describe its electronic nature

Dative covalent bond/coordinate bond: the 2 electrons in the bond come from 1 atom (in this case, the O in the water ligand)

200

What is the shape and color of [CoCl₄]^2- and [Cu(H₂O)₆]²⁺?

[CoCl₄]^2-: deep blue, tetrahedral

[Cu(H₂O)₆]²⁺: pale blue, octahedral

300

Write the reaction of Fe³⁺ in excess OH^- aqueous solution. What qualitative changes do you expect to see?

[Fe(H₂O)₆]³⁺ + 3OH^- --> [Fe(H₂O)₃(OH)₃]³⁺ + 3H₂O

You would observe a brown precipitate form from the yellow solution

400

In solution, 1 molecule [Co(H₂O)₆]²⁺ reacts with 3 molecules of ethane-1,2-diamine to form a new complex ion. Write the reaction & explain why this might be favorable.

[Co(H₂O)₆]²⁺ + 3H₂NCH₂CH₂NH₂ --> [Co(H₂NCH₂CH₂NH₂)₃]²⁺ + 6H₂O

This is favorable because the number of particles increases, therby increasing entropy (chelate effect)