chemistry chap 10 (redox reaction)

What is a redox reaction in oxygen atoms? (gain/loss in…)

Oxidation is the gain of oxygen atoms

Reduction is the loss of oxygen atoms

What is a redox reaction in hydrogen atoms? (gain/loss in…)

Oxidation is the loss of hydrogen atoms

Reduction is the gain of hydrogen atoms

What is a redox reaction in electrons? (gain/loss in…)

Oxidation is the loss of electrons.

Reduction is the gain of electrons.

What is the redox reaction for oxidation state? (Increase/decrease)

Oxidation is the increase in oxidation state.

Reduction is the decrease in reduction state.

How do you find the oxidation state of atoms and ions?

1. Atoms of the same element (e.g. single atoms; molecules of an element; metallic elements) have oxidation state of 0.

2. Compound with no net charge: all oxidation states of constituent elements add up to 0.

3. Ion with a net charge: all oxidation states of constituent elements will add up to that net charge.

State the oxidation states of common elements as ions/in compounds

Group 1 (Na+, K+): +1

Group 2 (Mg2+, Ca2+): +2

Hydrogen: +1

Oxygen: -2

Chlorine: -1

Fluorine: -1

What is an oxidizing agent?

Oxidising agent is a substance that causes another substance to be oxidised (while itself is reduced)

What is a reducing agent?

Reducing agent is a substance that causes another substance to be reduced (while itself is oxidized)

How do you test for a reducing agent?

To test if the unknown is an oxidising agent, a reducing agent is added to it.

1. Add acidified potassium iodide (KI) solution

   • Results: Turns from colourless to yellow-brown

     eqn: 2I- (aq) → Fe3+ (aq) + e-

2. Add acidified iron(II) sulfate solution

   • Results: Turns from green to yellow

     eqn: Fe2+ (aq) →Fe3+ (aq) + e-

3. Dip a piece of starch-iodide paper in the unknown solution.

   • Results: Starch iodide paper turns from white to blue-black

     I^- is oxidised to I₂. I₂ reacts with starch to give blue-black.

How do you test for an oxidizing agent?

To test for a reducing agent, an oxidising agent is added to it.

1. For gases: add a piece of filter paper soaked with acidified potassium manganate(VII), KMnO₄, at the mouth of the test tube. 

   For solutions: add acidified potassium manganate(VII), KMnO₄, to the unknown solution.

   • Results: Turns from purple to colourless / decolourises

     eqn: MnO4- (aq) + 8H+ (aq) →Mn2+ (aq) + 4H2O (l)

What are the general rules of calculating oxidation state?

Rule 1

• The oxidation state of an element is always 0
  

Rule 2

• The oxidation state of a simple ion is the same as its charge

Rule 3

• The oxidation states of all the atoms or ions in a compound add up to 0