Redox Reaction

In which of the following reactions is the underlined substance reduced?

• Cl₂ + 2I^– –> 2Cl^- + I₂

• Zn + H₂SO₄ –> ZnSO₄ + H₂

• Fe²⁺ + H₂O₂ –> Fe³⁺ + H₂O

• CuO + H₂ –> Cu + H₂O

Which conversion involves the smallest change in oxidation number of the underlined element?

• C(s) –> CO_{2 (g)}

• NO₃^-(aq) –> NO₂(g)

• SO₃^2-(aq) –> SO₄^2-(aq)

• MnO₄^-(aq) –> Mn²⁺(aq)

The oxidation states of chlorine in ClO₄^- and Cl₂O are respectively

• +1 and +3

• +3 and +7

• +7 and +1

• +7 and +2

Which statement is true about oxidizing agents?

Hint: oxidizing agents are themselves reduced. Hence, they ....... electrons.

• Their oxidation state is zero

• They are easily oxidized

• They never contain hydrogen

• They readily accept electrons

What does an oxidizing agent do? They help other reducing agent being oxidised by themselves

• It turns acidified potassium dichromate (VI) green

• It turns potassium manganate (VII) colorless

• It turns Universal Indicator red

• It turns aqueous potassium iodide brown

The oxidation number of manganese, Mn in Mn(NO₃)_{2. Hint: N has +5, O has -2. Do like this -> Mn + 2 (N+3O) calculation}

• -1

• +2

• 0

• -3

• +6

The equation for the reaction between zinc metal and copper (II) sulfate solution is

Zn (s) + CuSO₄ (aq) ==> ZnSO₄ (aq) + Cu (s).

The net ionic equation is:

Zn (s) + Cu²⁺ (aq) ==> Zn²⁺ (aq) + Cu (s).

Hint: CuSO4 is blue in colour.

Which statements are CORRECT? (tick 3 CORRECT ANSWERS) Take your time here. I give 10min here.

• Zn is oxidised because the oxidation number increases from 0 in Zn to +2 in Zn ²⁺

• The blue colour of CuSO₄ remains unchanged throughout the reaction, before and after the reaction.

• Before experiment starts, the CuSO₄ solution is blue. At the end of the experiment, the blue colour fades (decolourised) at times. Pink/brown deposit of Cu metal coats the Zn surface

• Zinc metal is oxidising agent in this reaction. It accepts 2 electrons from Cu²⁺ ions (Zn + 2e ==> Zn²⁺)

• CuSO₄ is reduced to Cu. Copper(II) ion in CuSO₄ gains electrons to become Cu. A gain of electrons is reduction (Cu²⁺ + 2e- ==> Cu)

Which of the following statements are INCORRECT?

[ tick 2 correct answers here]

• An oxidising agent is an electron acceptor

• An reducing agent is an electron donor

• Reduction is defined as the loss of electrons

• Reduction is defined as the removal of hydrogen atoms

• Oxidation occurs when oxygen atoms are gained and electrons are lost

Which statements are CORRECT? [tick 3 correct answers]

• The oxidation number of nitrogen in NO₃^- is +5

• The oxidation number of sulfur in an ion of sulfate, SO₄^2- = +6

• The oxidation number of hydrogen in calcium hydride, CaH₂ is +1

• The oxidation number of carbon in CO₂ is +4

• The oxidation number of nitrogen in NH₃ is +3

Define oxidising agent and reducing agent correctly. Tick 2 correct answers

• Oxidising agent is substance which oxidises another substance during a redox reaction.

  Reducing agent is substance which reduces another substance during a redox reaction.

• In simple word

  Oxidising agents are reduced. KMnO4 and K2Cr2O7

  Reducing agents are oxidised. KI.

• Oxidising agent is substance which reduces another substance during a redox reaction.

  Reducing agent is substance which oxidises another substance during a redox reaction.

• In simple word

  Oxidising agents are oxidised. KI.

  Reducing agents are reduced. KMnO4 and K2Cr2O7