Question

Explain the following:

Cleansing action of soap
Calcination and Roasting
Activity series of metals

Hint:

- Soap molecules have a hydrophilic (water-loving) and hydrophobic (water-hating) end, which helps in cleaning oil and grease. - Calcination involves heating in the absence of air, while roasting occurs in the presence of oxygen. - The activity series helps predict which metals will displace others in chemical reactions.

Answer 1

(i) Cleansing Action of Soap:
Soap is a surfactant that has both hydrophilic (water-attracting) and hydrophobic (water-repelling) ends. The cleansing action of soap is due to the ability of soap molecules to break the oil or grease particles into small droplets, which can be easily washed away with water.
Mechanism of Cleansing:
- The hydrophobic end of the soap molecule dissolves in the oil or grease.
- The hydrophilic end of the soap molecule interacts with water.
- This results in the formation of micelles, which trap the oil and grease particles in the center.
- The micelles are washed away with water, taking the dirt along with them.
(ii) Calcination and Roasting:
Calcination and roasting are two methods used in metallurgy to convert ores into metals, but they differ in the processes involved:
1. Calcination:
- Calcination is the process of heating an ore in the absence of air or in a limited supply of air.
- This is done to remove volatile components like water, carbon dioxide, or sulfur.
- Example: Heating limestone (\( \text{CaCO}_3 \)) to form quicklime (\( \text{CaO} \)): \[ \text{CaCO}_3 \xrightarrow{\text{heat}} \text{CaO} + \text{CO}_2 \]
2. Roasting:
- Roasting is the process of heating an ore in the presence of excess air or oxygen.
- It is typically used for ores containing sulfides, which are converted into oxides.
- Example: Heating copper sulfide (\( \text{Cu}_2\text{S} \)) in air to form copper oxide (\( \text{CuO} \)): \[ 2\text{Cu}_2\text{S} + 3\text{O}_2 \rightarrow 2\text{CuO} + 2\text{SO}_2 \]
(iii) Activity Series of Metals:
The activity series is a list of metals arranged in order of their reactivity, from the most reactive to the least reactive. It helps predict the outcome of displacement reactions and the extraction of metals.
Key Points:
- The metals at the top of the series, such as potassium, sodium, and calcium, are highly reactive and readily lose electrons.
- Metals at the bottom, such as gold and platinum, are less reactive and do not easily participate in reactions.
- Example of Activity Series:
- Potassium (\( \text{K} \)) is more reactive than sodium (\( \text{Na} \)), and sodium is more reactive than iron (\( \text{Fe} \)).
- A more reactive metal will displace a less reactive metal from its compound.

Example of Displacement Reaction:
\[ \text{Zn} + \text{CuSO}_4 \rightarrow \text{ZnSO}_4 + \text{Cu} \]
In this reaction, zinc displaces copper from copper sulfate because zinc is more reactive than copper.