Chemical Reactions

Step 1: Understanding the Concept:
This is a single displacement reaction. A more reactive metal displaces a less reactive metal from its salt solution.

Step 2: Detailed Explanation:
Iron ( ) is placed higher than Copper ( ) in the reactivity series, meaning it is more reactive.
When an iron nail is placed in an aqueous solution of copper sulfate ( ), iron displaces copper from the solution to form iron(II) sulfate ( ).
Observations:
1. The blue color of the copper sulfate solution gradually fades and turns light green due to the formation of iron(II) sulfate.
2. A reddish-brown coating of metallic copper is deposited on the surface of the iron nail.
Chemical Equation:


Step 3: Final Answer:
Iron displaces copper. The blue solution turns green, and brown copper coats the nail.

Step 1: Understanding the Concept:
Balancing an equation ensures the Law of Conservation of Mass is satisfied, meaning the number of atoms of each element is equal on both the reactant and product sides.

Step 2: Key Formula or Approach:
Count atoms on both sides and use coefficients to balance them step-by-step.

Step 2: Detailed Explanation:
Unbalanced equation:
Reactant side: , ,
Product side: , ,
1. Balance Fe atoms: Multiply Fe on the reactant side by 3.

2. Balance O atoms: Multiply on the reactant side by 4.

3. Balance H atoms: Now there are atoms on the reactant side. Multiply on the product side by 4.

Check: on both sides. The equation is balanced.

Step 3: Final Answer:
The balanced equation is .

Step 1: Understanding the Concept:
Fats and oils undergo oxidation when exposed to oxygen in the air, leading to a foul smell and bad taste. This is called rancidity.

Step 2: Detailed Explanation:
To preserve oily and fatty foods (like potato chips), food manufacturers flush the packaging bags with Nitrogen gas before sealing them.
Nitrogen is an inert, unreactive gas at room temperature.
By replacing the oxygen-rich air inside the packet with nitrogen, the oxidation process of the fats and oils is stopped or significantly slowed down.

Step 3: Final Answer:
They are flushed with nitrogen to provide an inert environment that prevents oxidation and rancidity of the food.

Step 1: Understanding the Concept:
Oxidation is the gain of oxygen or loss of electrons.
Reduction is the loss of oxygen or gain of electrons.

Step 2: Detailed Explanation:
In the given reaction:
1. Look at Sodium ( ): It starts as elemental Sodium and gains oxygen to become Sodium oxide ( ). Gaining oxygen means it is oxidized.
2. Look at Oxygen ( ): In terms of electrons, elemental Oxygen (oxidation state 0) gains electrons from Sodium to become oxide ions ( ) in . Gaining electrons means it is reduced.

Step 3: Final Answer:
Sodium is oxidized, and Oxygen is reduced.

Step 1: Understanding the Concept:
A physical change alters the state or appearance but not the chemical composition.
A chemical change results in the formation of new substances with different chemical properties.

Step 2: Detailed Explanation:
Let's analyze the options:
(A) Rusting of iron forms a new compound (iron oxide), so it's a chemical change.
(B) Respiration breaks down glucose to form carbon dioxide and water, so it's a chemical change.
(C) Melting of wax only changes solid wax to liquid wax. The chemical composition remains the same. It is a physical change.
(D) Burning of wax reacts wax with oxygen to produce carbon dioxide and water vapor, so it's a chemical change.

Step 3: Final Answer:
Melting of wax is a physical change, not a chemical change.