KEMINO Review 2

What is the oxidation state of oxygen is H₂O₂

• +2

• -2

• +1

• -1

Answer explanation

Oxidation state = number of electrons gained or removed from the atom

charge = total number of protons - electrons

oxygen is usually -2

The oxidation state of G1 Metals is _____ and the oxidation state of G7 Halogens is _____

• +1, +7

• +1, -1

• +2, +7

• +2, -1

Answer explanation

G2 metals is +2 not G1

The oxidation state in Fe (s) is

• -3

• 0

• +3

• +2

Answer explanation

free / uncombined elements have oxidation state of 0

but ions Fe^3+/2+ will have O.S. of the charge (i.e. +3/+2)

What is the oxidation state of Hydrogen in NaH

• +1

• 0

• -1

• -2

Answer explanation

Sum of O.S. for element = O.S. in its compound

so in this case Hydrogen is -1 instead of usual +1 since it is a metal hydride with Sodium (O.S. +1)

What is the theoretical maximum number of O.S. that an element can have

• 1

• 3

• 6

• 9

Answer explanation

within the range of being isoelectronic with a noble gas e.g. Nitrogen can range from -3 to +5

What oxidizes and reduces in the following equation:

2Mg (s) + O₂ (g) --> 2MgO (s)

• Mg oxidizes

• Mg reduces

• O₂ oxidizes

• O₂ reduces

Answer explanation

An Ox = increasing in oxidation state

Red Ca = decreasing in oxidation state

OILRIG for gain / loss in electrons

oxdiant reduces and reductant oxidizes

order of steps in balancing redox eqn.

1 - add OH- to cancel out H+ IF it rxn is done in alkaline conditions

2 - H₂O to balance out oxygen and H⁺ to balance out Hydrogen

3 - write unbalanced eqn as 2 half equations for red and ox

4 - in half equations, balance out all molecules except H and O

5 - balance electrons between half equations

6 - in half equations balance charges with electrons

7 - combine half equations and cancel out common species

• 1, 2, 3, 4, 5, 6, 7

• 7, 6, 5, 4, 3, 2, 1,

• 1, 3, 2, 4, 6, 7, 5

• 3, 4, 2, 6, 5, 7, 1

• 2, 6, 4, 7, 5, 3, 1

Reaction where same element of different oxidation state reacts to form the same element in intermediate oxidation state

• disproportionation

• comproportionation

Answer explanation

disproportionation is the opposite. intermediate O.S. element reduces and oxidizes at the same time into 2 different O.S. in products side

which electrochemical cell is spontaneous and produces electricity from chemical energy

• downs cell

• galvanic/voltaic

• electrolytic

• all

Answer explanation

electrochemical cells convert between electrical and chemical energy

downs cell is a voltaic cell (electricity used to drive non sponty redox rxn) which does electrolysis of molten NaCl

Side on the left of galvanic cell diagram, where oxidation occurs

• anode

• cathode

• electrode

• chemode

Answer explanation

cathode is on the right, where reduction occurs