RBSE Solutions Class 12 Chemistry Chapter 17 Chemistry in Daily Life

RBSE Class 12 Chemistry Chapter 17 Text Book Questions

RBSE Class 12 Chemistry Chapter 17 Very Short Answer Type Questions

 

Question 1. What is saponification?
Answer: Soaps are special salts made from sodium or potassium and long-chain fatty acids, often having 15 to 18 carbon atoms. Examples include stearic acid and palmitic acid. The process of making these soaps is called saponification. For example, sodium palmitate (\( \text{C}_{15}\text{H}_{31}\text{COONa} \)) is a common type of soap.
This reaction happens when fats or oils (like triglycerides) react with a strong base (like NaOH), producing soap and glycerol. Saponification is essentially the alkaline hydrolysis of an ester, producing soap and glycerol.
The process can be shown as:
\( \begin{array}{l} \text{CH}_2\text{-O-CO-R}_1 \\ | \\ \text{CH-O-CO-R}_2 \\ | \\ \text{CH}_2\text{-O-CO-R}_3 \end{array} \text{ (Oil or Fat)} + 3\text{NaOH} \xrightarrow{\text{Saponification}} \begin{array}{l} \text{CH}_2\text{-OH} \\ | \\ \text{CH-OH} \\ | \\ \text{CH}_2\text{-OH} \end{array} \text{ (Glycerol)} + \begin{array}{l} \text{R}_1\text{COONa} \\ \text{R}_2\text{COONa} \\ \text{R}_3\text{COONa} \end{array} \text{ (Soap)} \)
Here, R can represent groups like \( \text{-C}_{15}\text{H}_{31} \), \( \text{-C}_{17}\text{H}_{33} \) or \( \text{-C}_{17}\text{H}_{35} \).
In simple words: Saponification is how we make soap. It's a chemical process where fats or oils mix with a strong alkali (like lye) to create soap and glycerol.

🎯 Exam Tip: Remember that soaps are salts of fatty acids, and saponification is specifically the alkaline hydrolysis of fats or oils.

 

Question 2. What are soft and hard soaps?
Answer: Soft soaps are made from the potassium salts of fatty acids, which gives them a softer consistency. Hard soaps, on the other hand, are produced from the sodium salts of fatty acids and are typically solid and firm. The specific alkali used during saponification determines whether the soap will be soft or hard.
In simple words: Soft soaps use potassium salts, making them gentle, while hard soaps use sodium salts, making them firm.

🎯 Exam Tip: Always associate potassium with soft soaps and sodium with hard soaps to easily recall their composition.

 

Question 3. What are detergents?
Answer: Detergents are cleaning agents designed to overcome the issues soaps face when used with hard water. They are chemicals that possess all the cleaning abilities of soaps but are not chemically considered soaps themselves. This allows them to work efficiently in both soft and hard water without forming scum. Unlike soaps, detergents do not form insoluble precipitates with hard water ions.
For example, sodium lauryl sulphate \( (\text{CH}_3(\text{CH}_2)_{10}\text{CH}_2\text{OSO}_3\text{Na}) \) is a common detergent.
In simple words: Detergents are cleaning chemicals that act like soap but work better in hard water because they don't form sticky residues.

🎯 Exam Tip: Highlight that detergents are effective in hard water due to their chemical structure which prevents the formation of insoluble salts.

 

Question 4. What are biodegradable and non-biodegradable detergents?
Answer:
Biodegradable detergents: These are detergents that can be broken down naturally by tiny living things, called microorganisms, that live in water. They are environmentally friendly because they don't last long in nature. It has been found that detergents with straight chains of hydrocarbons are easily broken down by these organisms.
For example, sodium lauryl sulphate is a biodegradable detergent.
Non-biodegradable detergents: These detergents cannot be broken down by microorganisms. They remain in the environment for a long time, leading to pollution of water bodies. Often, detergents with branched hydrocarbon chains are non-biodegradable because their structure is harder for microbes to process.
An example of a non-biodegradable detergent is sodium 4-(1, 3, 5, 7 tetramethyl octyl) benzenesulfonate.
In simple words: Biodegradable detergents break down naturally and are good for the environment, while non-biodegradable ones do not break down easily and can cause pollution.

🎯 Exam Tip: The key difference lies in the hydrocarbon chain structure: straight chains are biodegradable, while branched chains are non-biodegradable.

 

Question 5. Give an example of cationic detergent.
Answer: Cationic detergents have a positively charged head part, which makes them useful as germicides. A common example of this type of detergent is cetyltrimethyl ammonium bromide.
Its structure can be represented as:
\( \begin{array}{c} \quad \text{CH}_3 \\ \quad | \\ \text{H}_3\text{C}-(\text{CH}_2)_{15}\text{-}\overset{+}{\text{N}}\text{-CH}_3 \quad \text{Br}^- \\ \quad | \\ \quad \text{CH}_3 \end{array} \)
In simple words: Cetyltrimethyl ammonium bromide is an example of a cationic detergent, which means it has a positive charge and can kill germs.

🎯 Exam Tip: Remember that cationic detergents are often used in hair conditioners and as antiseptics because of their positive charge.

 

Question 6. What are chromophores? Give an example.
Answer: Chromophores are specific parts of organic molecules that are responsible for the color we see. They absorb light at certain wavelengths, making the compound appear colored. These structures usually contain double or triple bonds.
Examples of chromophores include:
\( \text{O=C} \)
\( \text{-C=C-} \)
In simple words: Chromophores are the parts of a molecule that make it colorful by soaking up some light and letting other colors pass through.

🎯 Exam Tip: Recall that chromophores typically contain unsaturated bonds (double or triple bonds) that allow them to absorb light in the visible region.

 

Question 7. What are auxochromes? Give an example.
Answer: Auxochromes are specific groups that do not create color on their own. However, when they are attached to a chromophore (the color-producing part of a molecule), they make the color stronger, deeper, and can also change the shade by shifting the light absorption to longer wavelengths. They effectively enhance the chromophore's ability to produce color because they possess lone pairs of electrons.
Examples of auxochromes include: \( \text{-OH} \), \( \text{-NH}_2 \), \( \text{-NHR} \), and \( \text{-NR}_2 \).
In simple words: Auxochromes are like boosters for color. They don't make color alone, but when added to a color-making part, they make that color much stronger and sometimes change its shade.

🎯 Exam Tip: Remember that auxochromes are electron-donating groups, which stabilize the excited state of the chromophore, leading to bathochromic shifts (red shift) and increased intensity.

 

Question 8. What are mordant dyes? Give an Example.
Answer: Mordant dyes need a special binding material, called a mordant (like a metal hydroxide), to stick to fabric. The mordant helps the dye attach strongly to the material. Interestingly, the color produced by the dye can change based on the specific metal ion used as the mordant. This makes them highly versatile for dyeing natural fibers.
Alizarin is an important example of a mordant dye.
In simple words: Mordant dyes need a special helper chemical called a mordant to properly color clothes, and the color can change depending on the mordant used.

🎯 Exam Tip: Always state that mordant dyes form a complex with the mordant and the fiber, ensuring colorfastness.

 

Question 9. What are triphenylmethane dyes? Give an example.
Answer: Triphenylmethane dyes are a class of dyes that are amino derivatives of triphenyl methane. They are known for their bright, intense colors and are often used to directly color materials like wool and silk. Malachite green is a prominent example from this group, valued for its blue-green hue.
Here is a partial structural representation from the source:

     C
    / \
   +
  NMeCl
 / \
Me-N-Me

In simple words: Triphenylmethane dyes are a type of colorful chemical, like malachite green, that can directly dye wool and silk. They have a specific three-ring structure.

🎯 Exam Tip: Focus on the triphenylmethane backbone and the intense colors produced by these dyes, along with a key example like malachite green.

 

Question 10. What are vat dyes? Give examples.
Answer: Vat dyes are a historical class of dyes known from ancient times. These dyes are insoluble in water, meaning they cannot directly color fibers. To be used, they must first be reduced in a special container (a "vat") to a soluble, colorless form (called the leuco form). This soluble form then enters the fiber. Once exposed to air, it oxidizes back to its insoluble, colored state, becoming trapped inside the fiber, which gives it excellent colorfastness.
The process involves oxidation and reduction steps to apply the dye effectively.
For example, Indigo is a well-known vat dye:


In simple words: Vat dyes are old dyes that don't mix with water. They are first changed to a soluble form, used to dye cloth, and then changed back to their colored, insoluble form inside the fabric.

🎯 Exam Tip: Emphasize the reversible reduction-oxidation process unique to vat dyes for their application and colorfastness.

RBSE Class 12 Chemistry Chapter 17 Long Answer Type Questions

 

Question 1. What are soaps? How are they prepared? Explain its cleansing actions.
Answer: Soaps are cleansing agents made from the sodium or potassium salts of higher fatty acids, which typically contain 15 to 18 carbon atoms. Common examples include salts of stearic acid and palmitic acid.

Preparation (Saponification): Soaps are prepared through a chemical process known as saponification. This involves heating fats or oils (which are triglycerides) with a strong alkali, such as sodium hydroxide (NaOH) or potassium hydroxide (KOH). This reaction breaks down the fat or oil into two main products: glycerol and the fatty acid salts, which are the soaps. This reaction is a type of alkaline hydrolysis of esters.
The process of saponification can be shown as:
\( \begin{array}{l} \text{CH}_2\text{-O-CO-R}_1 \\ | \\ \text{CH-O-CO-R}_2 \\ | \\ \text{CH}_2\text{-O-CO-R}_3 \end{array} \text{ (Oil or Fat)} + 3\text{NaOH} \xrightarrow{\text{Saponification}} \begin{array}{l} \text{CH}_2\text{-OH} \\ | \\ \text{CH-OH} \\ | \\ \text{CH}_2\text{-OH} \end{array} \text{ (Glycerol)} + \begin{array}{l} \text{R}_1\text{COONa} \\ \text{R}_2\text{COONa} \\ \text{R}_3\text{COONa} \end{array} \text{ (Soap)} \)
Here, R can represent groups like \( \text{-C}_{15}\text{H}_{31} \), \( \text{-C}_{17}\text{H}_{33} \) or \( \text{-C}_{17}\text{H}_{35} \).

Cleansing Action: The cleansing power of soaps comes from their unique molecular structure and the formation of micelles. Each soap molecule has a dual nature: a long, non-polar hydrocarbon tail that repels water (hydrophobic) and a short, polar, negatively charged ionic head that attracts water (hydrophilic).
Dirt, grease, and oil on clothes are typically non-polar. When soap is dissolved in water and a dirty cloth is introduced, the hydrophobic tails of the soap molecules penetrate the oily dirt, while the hydrophilic heads remain in the water. Many soap molecules surround each oil or grease particle, forming a tiny, spherical cluster called a micelle. In a micelle, the hydrophobic tails point inwards, trapping the dirt, while the hydrophilic heads point outwards into the water.
Because the outer surface of these micelles is negatively charged (due to the hydrophilic heads), they repel each other and stay suspended in the water, forming a stable emulsion. This prevents the dirt from reattaching to the fabric. The mechanical action of washing helps break off these dirt-laden micelles, which are then rinsed away with the water.
In simple words: Soaps are made by mixing fats with alkali. They clean by forming tiny balls (micelles) around dirt, pulling the dirt away from clothes into the water so it can be washed off.

🎯 Exam Tip: When explaining cleansing action, clearly describe the hydrophobic tail, hydrophilic head, and the micelle formation with negative surface charge that keeps dirt suspended.

 

Question 2. What are detergents? Give its classification and its cleansing action.
Answer: Detergents are cleaning agents similar to soaps but are not actual soaps. They are synthetic substances that work effectively even in hard water because they do not form insoluble precipitates with mineral ions like calcium and magnesium.

Classification of Detergents: Detergents are broadly categorized into three types based on the charge of their hydrophilic (water-attracting) part:
1. Anionic detergents: In these detergents, the active cleaning part carries a negative charge. They are commonly sodium salts of sulphonated long-chain alcohols or hydrocarbons, like sodium lauryl sulphate (\( \text{CH}_3(\text{CH}_2)_{10}\text{CH}_2\text{OSO}_3\text{Na} \)). They are widely used in laundry products and toothpastes.
2. Cationic detergents: These detergents have a positively charged active group. They are usually quaternary ammonium salts, such as cetyltrimethyl ammonium bromide (\( \text{CH}_3(\text{CH}_2)_{15}\overset{+}{\text{N}}(\text{CH}_3)_3\text{Br}^- \)). They are often found in hair conditioners and as germicides.
3. Non-ionic detergents: These detergents do not have any charged ions. Instead, their polar heads consist of long chains containing ether linkages. They are excellent for degreasing and are typically used in dishwashing liquids. Polyethylene glycol stearate is an example.

Cleansing Action: The cleansing action of detergents operates on the principle of micelle formation, much like soaps. A detergent molecule has a long, hydrophobic (water-repelling) hydrocarbon tail and a hydrophilic (water-attracting) polar head. When detergent is added to water containing dirt (often oily or greasy), the hydrophobic tails surround the oil/grease particles, while the hydrophilic heads orient outwards into the water. This forms spherical structures called micelles, with the dirt trapped inside.
The outer surface of these micelles is charged (for anionic and cationic detergents) or highly polar (for non-ionic), which causes them to repel each other and prevents the dirt from re-depositing on the fabric. This stable suspension of dirt-laden micelles can then be easily rinsed away with water. Detergents maintain this micelle-forming ability even in hard water, ensuring consistent cleaning.

In simple words: Detergents are cleaners that work like soaps but are better in hard water. They are split into three types: anionic (negative part cleans), cationic (positive part cleans), and non-ionic (no charge). They clean by forming tiny balls around dirt and washing it away.

🎯 Exam Tip: Clearly define each detergent type with an example and highlight how their molecular structure (hydrophobic tail, hydrophilic head) enables micelle formation for effective cleaning.

 

Question 3. Explain Witt theory for structural properties of dyes.
Answer: In 1876, Otto Witt developed the "Chromophore Auxochrome Theory" to explain how dyes get their color based on their chemical structure.

The important points of this theory are:
(i) Chromophores: These are specific unsaturated groups (containing double or triple bonds) within a molecule that absorb light and cause the compound to be colored. A compound must have at least one chromophore to show color. Examples include: \( \text{-C=C-} \), \( \text{-C=N-} \), \( \text{-C=O-} \), \( \text{-N=N-} \), and \( \text{-NO}_2 \).
(ii) Chromogens: These are organic compounds that contain chromophores. While they possess the potential for color, their color might be weak or unstable. The color-producing capacity increases with a higher number of chromophores in the molecule. Some chromophores like \( \text{-N=N-} \) can produce color on their own, while others like \( \text{>C=O} \) require more than one.
(iii) Auxochromes: These are groups that do not produce color by themselves but significantly deepen and intensify the color when attached to a chromophore. They also help in binding the dye to the fabric. Auxochromes are typically electron-donating groups, such as \( \text{-OH} \), \( \text{-NH}_2 \), \( \text{-NHR} \), and \( \text{-NR}_2 \). They work by extending the electron conjugation, which shifts the light absorption to longer wavelengths (known as a bathochromic shift) and makes the color more vibrant and fast.

This theory helps classify dyes based on their application properties, which relate to their structure:
(i) Direct Dyes: These dyes can be applied directly to fibers from a hot aqueous solution without a mordant. They are especially effective for fabrics that contain hydrogen bonds, such as cotton, rayon, wool, silk, and nylon.
Examples include Martius yellow and Congo red:

(ii) Acidic Dyes: These dyes are typically used in a slightly acidic solution and are generally sulphonic acid derivatives. They are water-soluble but do not have a strong affinity for cotton. Instead, they are used for dyeing silk, wool, and wood.
An example is Orange-I:

(iii) Basic Dyes: These dyes contain basic groups, such as the \( \text{-NH}_2 \) group, and react with anionic (negatively charged) sites on the fabric. They are commonly used to dye nylon and polyester, which often have such sites.
An example is Aniline yellow:

In simple words: Witt's theory explains why chemicals have color by looking at their parts. Some parts (chromophores) make color, and other parts (auxochromes) make the color stronger and help it stick. Dyes can be direct, acidic, or basic depending on how they are used and what they stick to.

🎯 Exam Tip: Structure your answer by clearly defining chromophores, chromogens, and auxochromes, providing examples for each. Then, explain how these concepts apply to different dye types.

 

Question 5. Classify dyes on the basis of structure.
Answer: Dyes can be classified based on their chemical structure, which significantly influences their properties and how they interact with different fabrics. Here are some major structural classifications:

(i) Nitro and Nitroso Dyes: These are older classes of dyes characterized by the presence of nitro (\( \text{-NO}_2 \)) or nitroso (\( \text{-NO} \)) groups, which act as their primary chromophores. Hydroxyl (\( \text{-OH} \)) groups are typically present as auxochromes, enhancing the color and dye binding. An example is picric acid.
Examples include 1-Nitroso-2-napthol and 2-Nitroso-1-napthol:

(ii) Diphenyl Methane Dyes: These dyes possess a basic structure derived from diphenylmethane. They are known for their bright colors, although specific examples and structures are often discussed in conjunction with triphenylmethane dyes.

(iii) Triphenyl Methane Dye: These are dyes that are amino derivatives of triphenylmethane. They are known for producing bright colors and are directly used to color materials such as wool and silk. Malachite green is a prominent example.

\( \text{Me}_2\text{N} \)
         \( \text{C} \)
        \( + \)
     \( \text{NMe}_2 \text{Cl} \)

Malachite Green
(iv) Phthalein Dyes: This class of dyes is formed by the chemical combination of phthalic anhydride with phenolic compounds. They can sometimes contain a xanthene ring structure. Phenolphthalein (used as an acid-base indicator) and fluorescein (a fluorescent dye) are important examples of phthalein dyes, with fluorescein being a xanthene derivative.
The general structure involves complex ring systems, as shown below for a common phthalein dye:

(v) Azo Dyes: This is the largest and most varied group of synthetic dyes, capable of producing nearly all colors. Their defining characteristic is the presence of an azo group (\( \text{-N=N-} \)), which acts as the chromophore responsible for their color. They are highly versatile and widely used across many industries.
In simple words: Dyes are grouped by their main chemical structure. Some have nitro or nitroso parts, others are built on methane structures like triphenylmethane (e.g., malachite green). Phthalein dyes come from combining certain compounds, and azo dyes are the biggest group, known for their N=N bond that makes them colorful.

🎯 Exam Tip: For each structural classification, remember to name the characteristic chromophore or structural feature and provide a relevant example.

 

Question 5. Classify dyes on the basis of structure.
Answer: Dyes are classified by their chemical structure into several main types:
(iii) Triphenyl Methane Dyes: These dyes are derived from triphenyl methane and are amino derivatives. A notable example is malachite green, which is used to directly color materials like wool and silk.

\[ \text{Me}_2\text{N}-\langle \text{Benzene Ring} \rangle -\overset{+}{\text{C}}=\langle \text{Benzene Ring} \rangle =\text{NMe}_2 \text{ Cl}^- \]

(iv) Phthalein Dyes: These compounds are formed when phthalic anhydride reacts with phenolic compounds. Phenolphthalein is an important example that has a phthalein ring structure. Fluorescein is another example, which is a xanthene derivative. These dyes are widely used in indicators and for their vibrant colors.

\[ \text{HO}-\langle \text{Benzene Ring} \rangle -\text{C}=\text{C}-\text{O}-\text{C}=\text{C}-\langle \text{Benzene Ring} \rangle -\text{OH} \]

(v) Azo – Dyes: This is the largest group of synthetic dyes. They are recognized by the presence of an azo group (\( \text{-N=N-} \)) in their chemical structure. Azo dyes come in almost all colors and are very common due to their versatility in dyeing different materials.

(vi) Indigo Dyes: This is a very important group of natural dyes. The dye is traditionally extracted from the Indigofera tinctoria plant, which belongs to the bush pea family. Indigo dye is famous for its blue color. These dyes have been used since ancient times. This type of dye is insoluble in water and cannot directly dye fibers without a special process called vat dyeing.

\[ \text{O=C}-\overset{\text{H}}{\text{N}}-\text{C}=\text{C}-\overset{\text{N}}{\text{H}}-\text{C=O} \]

(vii) Anthraquinone Dyes: These dyes are based on the anthraquinone structure, which features a carbonyl group (\( >\text{C=O} \)) as the chromophore. These dyes can be used with a mordant (a binding material like metal hydroxide) to produce different colors depending on the metal ion used. For instance, alizarin, an important anthraquinone dye, can give various colors with different metal ions like pink with \( \text{Al}^{3+} \), black-violet with \( \text{Fe}^{3+} \), brown-violet with \( \text{Cr}^{3+} \), blue with \( \text{Ba}^{2+} \), and violet with \( \text{Mg}^{2+} \). This ability to change color makes them valuable in textile dyeing.

(viii) Heterocyclic dyes: These dyes are characterized by having at least one cyclic ring in their structure that contains atoms other than carbon (like nitrogen, oxygen, or sulfur). This is a broad and constantly expanding category as new dyes with such structures are continually being discovered. An example is Acriflavine, which is often used as an antiseptic dye.
In simple words: Dyes are grouped by how their molecules are built. Some come from a three-ring carbon structure (triphenyl methane), others from a specific acid (phthalic acid), and many have a special nitrogen-nitrogen bond (azo dyes). Natural dyes like indigo come from plants. Some dyes have a unique ring of atoms (heterocyclic), and others can change color depending on the metal they are mixed with (anthraquinone). This helps us understand how they give color.

🎯 Exam Tip: When classifying dyes, remember to provide a brief description of each type, mention key structural features (like the azo group or anthraquinone base), and include one or two clear examples. Understanding the basic chemical group responsible for the color helps you remember the classification.