CR Chapter 10 Redox '23-24

If in a reaction, copper is reduced; its number of electrons has (a)   .

• increased

• decreased

• remained constant

• varies randomly

Answer explanation

When copper is reduced in a reaction, it gains electrons, so the number of electrons increases. Therefore, the correct answer is increased.

When a lithium atom forms an Li⁺¹ ion, the lithium atom (a)  

• loses an electron

• gains a proton

• gains an electron

• loses a proton

Answer explanation

When a lithium atom forms an Li+1 ion, it loses an electron, resulting in a positive charge.

In a voltaic cell, reduction happens at the (a)   .

• cathode

• anode

• salt bridge

• voltmeter

Answer explanation

In a voltaic cell, reduction happens at the cathode, making it the correct choice.

In a voltaic cell, oxidation happens at the...

• anode

• cathode

• salt bridge

• voltmeter

Answer explanation

In a voltaic cell, oxidation happens at the anode, making it the correct choice.

The oxidation number of nitrogen in N₂ is

Mathematical Equivalence

ON

What is oxidation number of P in K₃PO₄?

• +1

• +5

• -2

• -3

Answer explanation

The oxidation number of P in K3PO4 is +5 because the sum of the oxidation numbers in a compound is zero, and K has an oxidation number of +1 and O has an oxidation number of -2.

What is the oxidation number of Br in (BrO₃)^-1?

• +3

• -2

• +5

• +2

Answer explanation

The oxidation number of Br in (BrO3)-1 is +5 because the overall charge of the ion is -1, and the oxidation number of O is -2, so Br must be +5 to balance the charge.

How would you write the electrons in the half reaction O₂ → 2O^-2 ?

• +4e^- on the products

• +4e^- on the reactants

• +2e^- on the products

• +2e^- on the reactants

Answer explanation

The correct choice is +2e^- on the reactants because electrons are added to the reactant side to balance the charge in the half reaction.

In the reaction 2Ca(s) + O₂(g) → 2CaO(s), calcium is (a)  

• oxidized

• reduced

• synthesized

• none of the above

Answer explanation

In the given reaction, calcium gains oxygen atoms, indicating it is oxidized. This is evident as it goes from an oxidation state of 0 in Ca(s) to +2 in CaO(s).

What is the oxidation number of Fe in FeO?

• +1

• -1

• +2

• -2

Answer explanation

The oxidation number of Fe in FeO is +2 because oxygen typically has an oxidation number of -2, making Fe in FeO have an oxidation number of +2 to balance the charges.