Oxidation Numbers

Author:Lawrie Ryan & Roger Norris
AS and A Level
IMPORTANT

Important Questions on Oxidation Numbers

EASY
IMPORTANT

When KBr reacts with hydrazine, N2H4, nitrogen gas is evolved.

2KBrO3+3N2H4         2KBr+3N2+6H2O

Explain, using oxidation numbers, why 2 moles of KBrO3 react with 3 moles of N2H4?

EASY
IMPORTANT

When KBr reacts with hydrazine, N2H4, nitrogen gas is evolved.

2KBrO3+3N2H4         2KBr+3N2+6H2O

Deduce the oxidation number change for each nitrogen atom when N2H4 is converted to N2.

EASY
IMPORTANT

When KBr reacts with hydrazine, N2H4, nitrogen gas is evolved.

2KBrO3+3N2H4         2KBr+3N2+6H2O

Deduce the oxidation number change of the bromine atom when KBrO3 is converted to KBr.

EASY
IMPORTANT

The compound KBrO3 decomposes when heated:

2KBrO3            2KBr+3O2

State the oxidation number of bromine in KBr.

EASY
IMPORTANT

The compound KBrO3 decomposes when heated:

2KBrO3            2KBr+3O2

State the oxidation number of bromine in KBrO3.

EASY
IMPORTANT

When a salt containing iodide ions is warmed with concentrated sulphuric acid and MnO2, iodine is evolved:

2I-+MnO2+6H++2SO42-           I2+Mn2++2HSO4-+2H2O

Deduce the oxidation number of S in the SO42- ion.

EASY
IMPORTANT

Iodine, I2, reacts with thiosulphate ions S2O32-, to form iodide ions, I-, and tetrathionate ions, S4O62-as I2+2S2O32-               2I-+S4O62-. State the oxidation number of each sulphur atom in a S4O62- ion.

EASY
IMPORTANT

Iodine, I2, reacts with thiosulphate ions S2O32-, to form iodide ions, I-, and tetrathionate ions, S4O62-as I2+2S2O32-               2I-+S4O62-. State the oxidation number of each sulphur atom in a S2O32- ion.

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IMPORTANT

Aluminium reacts with hydrochloric acid to form aluminium chloride, AlCl3, and hydrogen. This is a redox reaction. Deduce the change in oxidation number when a hydrogen ion turns into a hydrogen atom.

EASY
IMPORTANT

The unbalanced equation for the reaction of sulphur dioxide with bromine is as shown below:

SO2+Br2+H2O              SO42-+Br-+H+

State the change in oxidation number for each bromine atom.

EASY
IMPORTANT

The unbalanced equation for the reaction of sulphur dioxide with bromine is as shown below:

SO2+Br2+H2O              SO42-+Br-+H+

State the change in oxidation number for each S atom.

EASY
IMPORTANT

The unbalanced equation for the reaction of sulphur dioxide with bromine is as shown below:

SO2+Br2+H2O              SO42-+Br-+H+

State the oxidation number of bromine in Br-.

EASY
IMPORTANT

The unbalanced equation for the reaction of sulphur dioxide with bromine is as shown below:

SO2+Br2+H2O              SO42-+Br-+H+

State the oxidation number of bromine in Br2.

EASY
IMPORTANT

The unbalanced equation for the reaction of sulphur dioxide with bromine is as shown below:

SO2+Br2+H2O              SO42-+Br-+H+

State the oxidation number of sulphur in SO42-.

EASY
IMPORTANT

The unbalanced equation for the reaction of sulphur dioxide with bromine is as shown below:

SO2+Br2+H2O              SO42-+Br-+H+

State the oxidation number of sulphur in SO2.

EASY
IMPORTANT

Calcium reacts with cold water to form calcium hydroxide, CaOH2, and hydrogen, H2. State the oxidation number of hydrogen in hydrogen gas.

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IMPORTANT

Calcium reacts with cold water to form calcium hydroxide, CaOH2, and hydrogen, H2. State the oxidation number of hydrogen in water.

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IMPORTANT

Calcium reacts with cold water to form calcium hydroxide, CaOH2, and hydrogen, H2. State the oxidation number of calcium in calcium metal.

EASY
IMPORTANT

Look at the equation: Cr2O72-+2H++3SO2           2Cr3++H2O+3SO42-. Which one of these statements about the oxidation number changes is correct?