Maharashtra Board Class 7 Science Chapter 15 Materials We Use Solutions

Question a. The substance that helps water to remove dirt from the surface of material is called ................. .
Answer: soap
In simple words: Soap is a substance that helps water lift and remove dirt from surfaces, acting as a cleaning agent.

🎯 Exam Tip: Identify the primary function of soap in cleaning to correctly fill in the blank.

Question b. Fluoride is used in toothpaste to prevent ................. .
Answer: tooth decay
In simple words: Fluoride in toothpaste strengthens tooth enamel, helping to protect against cavities and tooth decay.

🎯 Exam Tip: Recall the main benefit of fluoride in oral hygiene products for health-related questions.

Question c. Soap is a salt of ................. and sodium hydroxide.
Answer: fatty acid
In simple words: Soaps are chemically formed when fatty acids react with an alkali like sodium hydroxide.

🎯 Exam Tip: Understand the basic chemical composition of soap, particularly the key components involved in its formation.

Question d. Synthetic detergents can be used in ................. water as well.
Answer: hard
In simple words: Synthetic detergents are effective for cleaning even in hard water, unlike traditional soaps that form scum.

🎯 Exam Tip: Note the key advantage of synthetic detergents over traditional soaps, especially concerning water type.

Question e. For construction purposes ................. Cement is the most commonly used cement.
Answer: white cement
In simple words: White cement is a common type of cement used for construction due to its versatile properties.

🎯 Exam Tip: Recognize the most common type of cement used in building and construction activities.

Exercise 2. Write Answers To The Following Questions.

Question a. How does the use of a detergent help to clean soiled clothes?
Answer:
1. A molecule of a detergent holds on to a water molecule at one end and an oil molecule at the other.
2. As a result the molecules of oil mix with the water.
3. This is how detergent acts on our soiled clothes. So detergent removes any oil or dirt sticking on to our clothes.
4. Due to the property of holding on to both oil and water, soap water spreads easily on many types of surfaces.
5. This property of spreading on a surface is called surface activity.
6. Detergents are surface active.
7. One effect of surface activity is lather formation.
In simple words: Detergents work by having molecules that attach to both water and oil/dirt, allowing the oil and dirt to mix with water and be washed away. Their surface activity helps them spread and form lather, enhancing cleaning.

🎯 Exam Tip: Focus on the dual nature of detergent molecules (hydrophilic and hydrophobic ends) and how this property aids in emulsification and dirt removal.

Question b. How will you check with the help of soap powder whether water is hard?
Answer:
1. In the hard water, (of a well or a tube-well), soap does not give lather but forms a scum.
2. As a result, soap loses its cleansing property. So with help of soap we will come to know that it is a hard water.
In simple words: To check for hard water, add soap powder to it; if it forms scum instead of lather, the water is hard. This is because minerals in hard water react with soap.

🎯 Exam Tip: The formation of scum instead of lather with soap is the definitive test for hard water. Highlight this observation in your answer.

Question c. What are the important ingredients of a tooth paste and what is the function of each?
Answer:
1. The important ingredients of a toothpaste are calcium carbonate and calcium hydrogen phosphate.
2. They remove the dirt on teeth. These ingredients also polish the teeth.
3. A certain proportion of fluoride in the tooth paste helps prevent tooth decay.
4. It is essential for the enamel covering of teeth.
In simple words: Toothpaste contains ingredients like calcium carbonate and calcium hydrogen phosphate for cleaning and polishing teeth, and fluoride to protect tooth enamel and prevent decay.

🎯 Exam Tip: List the primary abrasive and protective ingredients of toothpaste and their specific roles in oral hygiene.

Question d. What are the ingredients of cement?
Answer:
1. Cement is a dry, greenish grey powder with fine particles.
2. It is made from silica (sand), alumina (aluminium oxide), lime, iron oxide and magnesia (magnesium oxide).
In simple words: Cement is a fine powder composed primarily of silica (sand), alumina, lime, iron oxide, and magnesia.

🎯 Exam Tip: Remember the main mineral components that make up cement, distinguishing it from concrete.

Question e. What will happen if cement is not used in making concrete?
Answer:
1. In making concrete strong, the ingredients cement, water, sand and gravel should usually be mixed in the ratio of 1 : 2 : 3 : 0.5 to achieve maximum strength.
2. If enough cement is not used then the concrete will eventually fall apart, as cement is used as a binding agent.
In simple words: Cement acts as the binding agent in concrete, so without it, the mixture of sand, gravel, and water would not solidify and the concrete structure would lack strength and stability, eventually collapsing.

🎯 Exam Tip: Emphasize cement's critical role as a binding agent; its absence would result in a non-cohesive and unstable concrete structure.

Question f. Make a list of detergents, that you use. Answer: There are two types of detergents that we use, (a) Natural (b) Man-made detergents.
Answer:
1. Natural detergents are soap nut (ritha) soap pod (shikekai).
2. Man-made detergents are soap, hard soaps, soft soaps.
3. Synthetic detergents have taken the place of soap.
(i) Detergents are commonly available as powders or concentrated solution.
(ii) Detergents are for laundry, washing clothes and cleaning dishes.
4. Alkaline detergents used for hard surface cleaning.
In simple words: We use both natural detergents like soap nut and soap pod, and man-made detergents such as various types of soap and synthetic detergents available in powder or liquid forms for laundry, dishwashing, and general cleaning.

🎯 Exam Tip: Classify detergents into natural and man-made categories, providing examples for each and their common applications.

Question g. What should be expected from a detergent for delicate garments?
Answer:
1. Detergents should not be strong, they may spoil the texture, colour of delicate garments.
2. Now a days many detergents are available especially for woollen, delicate clothes.
3. They should not contain bleach, phosphorous which will harm delicate clothes.
In simple words: A detergent for delicate garments should be mild, free from harsh chemicals like bleach or phosphorus, and designed to preserve the fabric's texture and color.

🎯 Exam Tip: The key expectation for delicate garment detergents is gentleness and the absence of harsh chemicals that could damage fabric or color.

Question h. What is meant by surface activity? Name three chemicals responsible for the surface activity of various detergents.
Answer:
1. Due to the property of holding on to both oil and water, soap water spreads easily on many types of surfaces.
2. The property of a substance of spreading on a surface is called surface activity and the substance is called surfactant.
3. Detergents are surface active.
4. They increase the spreading and wetting ability of water by reducing its surface tension.
5. Chemicals responsible for the surface activity of various detergents is phenol, Aprotinin.
In simple words: Surface activity refers to a substance's ability to spread easily on a surface by reducing water's surface tension; substances with this property are called surfactants. Phenol and Aprotinin are examples of chemicals responsible for this action in detergents.

🎯 Exam Tip: Define surface activity as the ability to reduce surface tension and list chemicals (surfactants) that exhibit this property in detergents.

Exercise 3. What Are The Similarities And Differences Between:

Question a. Natural detergents and Man-made detergents
Answer:

In simple words: Natural detergents like soap nut are plant-based, contain saponin, are gentle on skin and fabric, and are naturally sourced. Man-made detergents, including soaps, are chemically produced from fatty acids and alkalis, can have chemicals that affect skin/fabric, and are manufactured.

🎯 Exam Tip: Differentiate between natural and man-made detergents based on their origin, chemical composition (e.g., saponin vs. fatty acid salts), and effects on skin and fabric.

Question b. Soap and Synthetic detergents
Answer:

In simple words: Soap, made from animal fat or oil and wood ash, is an older man-made detergent that struggles in hard water by forming scum. Synthetic detergents, derived from chemical processes involving fats or kerosene, are modern replacements that perform effectively even in hard water.

🎯 Exam Tip: Compare soap and synthetic detergents on their historical use, raw materials, and effectiveness in different water types, noting the advantages of synthetics.

Question c. Bath soap and Soap for washing clothes
Answer:

In simple words: Bath soaps are typically soft soaps (potassium salts of fatty acids) that dissolve easily, often containing perfumes and moisturizers for skin. Washing soaps are hard soaps (sodium salts of fatty acids) that dissolve less easily, sometimes with added germicides and anti-foaming agents for effective laundry cleaning.

🎯 Exam Tip: Distinguish between bath soap and washing soap based on their chemical composition (potassium vs. sodium salts of fatty acids), solubility, and common additives for their respective uses.

Question d. Modern cement and Ancient cement
Answer:

In simple words: Modern cement (Portland Cement) is precisely manufactured with specific proportions of lime, silica, alumina, iron oxide, and gypsum for construction. Ancient cement (Aqueous Cement), used by Romans, relied on volcanic ash mixed with moistened lime, known for its durability and crack prevention.

🎯 Exam Tip: Compare modern (Portland) and ancient (Roman/Aqueous) cements by their primary ingredients and historical usage, noting how each achieved durability and strength.

Exercise 4. Explain Why -

Question a. Soap cannot be used in hard water.
Answer:
1. In the hard water of a well or a tube well, soap does not give lather but forms a scum.
2. As a result soap loses its cleansing property. So soap cannot be used in hard water.
In simple words: Soap cannot be used in hard water because the minerals present in hard water react with soap to form insoluble scum, which prevents lather formation and reduces soap's cleansing effectiveness.

🎯 Exam Tip: The key reason is the reaction of soap with hard water minerals, leading to scum formation and loss of cleansing power.

Question b. Oil does not mix in water. However, oil and water become homogenous if a sufficient quantity of detergent is added.
Answer:
1. A molecule of a detergent holds on to a water molecule at one end and an oil molecule at the other.
2. As a result the molecules of oil mix with the water, and we will see that the water and oil have become homogenous and the colour of the mixture appears milky.
In simple words: Oil and water don't mix naturally, but adding detergent makes them appear homogenous because detergent molecules act as an intermediary, binding to both oil and water. This allows oil droplets to disperse evenly throughout the water, creating a milky mixture.

🎯 Exam Tip: Explain how detergent molecules, acting as surfactants, bridge the gap between immiscible oil and water, allowing them to form an emulsion and appear homogenous.

Question c. Synthetic detergents are superior to soap.
Answer:
1. Soap is a man-made detergent which has been in use since ancient times.
2. It was prepared by using animal fat and wood ash. In hard water, soap does not give lather, it loses its cleansing property.
3. So we can not use soap in hard water. Now synthetic detergents have taken the place of soap.
4. They can be used in hard water as well
5. Synthetic detergents have many more advanced properties like they are added with perfumes, conditioner for fabric, etc.
In simple words: Synthetic detergents are considered superior to soap because they are effective even in hard water, unlike soap which forms scum. Additionally, synthetic detergents often contain advanced additives like perfumes and fabric conditioners, enhancing their performance.

🎯 Exam Tip: Highlight the main advantages of synthetic detergents: effectiveness in hard water and the inclusion of advanced additives for improved performance.

Question d. Often coloured spots are formed on clothes during washing.
Answer:
1. Curry stains stick fast to the criss-crossing threads of the material of our clothes.
2. Curry contains turmeric a natural indicator which turns red in a basic solution.
3. Soaps are sodium salts of fatty acids and are basic in nature.
4. While washing the clothes, turmeric reacts with soap solution and turns red forming red spots on the clothes.
5. But the spots disappear after washing the clothes with plenty of water.
In simple words: Coloured spots, particularly red ones from curry stains, appear during washing because turmeric in curry acts as a natural indicator, turning red when it reacts with the basic soap solution. These spots usually disappear after rinsing with plenty of water.

🎯 Exam Tip: Explain the chemical reaction: turmeric (in curry) is a natural indicator that turns red in the basic pH of soap solution, causing the temporary red spots.

Question e. Tobacco masheri should not be used for cleaning teeth.
Answer:
1. Masheri is the smokeless form of tobacco. It is tobacco, containing teeth cleaning powder
2. It contains tobacco leaves.
3. Tobacco contains toxic and Carcinogenic chemicals which can cause cancer, oral cancer, mouth and throat cancer, gum disease, tooth decay.
4. Its use can cause abnormal delivery in pregnant women.
In simple words: Tobacco masheri should not be used for cleaning teeth because it is a smokeless tobacco product containing toxic and carcinogenic chemicals. These substances can lead to various health issues including oral cancer, gum disease, tooth decay, and complications during pregnancy.

🎯 Exam Tip: Emphasize the presence of toxic and carcinogenic chemicals in tobacco masheri and list the severe health risks associated with its use, especially for oral health and pregnant women.

Project:

Question 1. Visit a cement factory. See how cement is prepared and discuss the process.
Answer: [Text]
In simple words: Visiting a cement factory allows you to observe the entire manufacturing process, from raw material crushing and mixing to calcination in kilns and final grinding into cement powder.

🎯 Exam Tip: For a project, focus on observing and documenting the key stages of cement production, including raw material handling, clinker formation, and final grinding.

Question 2. Write a conversation based on cement houses, mud-houses and wattle-and-daub houses.
Answer: [Text]
In simple words: A conversation discussing cement, mud, and wattle-and-daub houses would compare their construction methods, durability, cost, environmental impact, and suitability for different climates and lifestyles.

🎯 Exam Tip: In a conversation, highlight the comparative strengths and weaknesses of each house type regarding materials, longevity, comfort, and historical context.

Exercise Fill In The Blanks:

Question 1. The principal ingredients of a toothpaste are ................. and ................. which remove the dirt on the teeth.
Answer: Calcium carbonate, calcium hydrogen phosphate
In simple words: Toothpaste uses calcium carbonate and calcium hydrogen phosphate as its main ingredients to effectively clean teeth by removing dirt.

🎯 Exam Tip: Identify the key abrasive compounds in toothpaste responsible for cleaning action.

Question 2. ................. in the toothpaste helps prevent tooth decay.
Answer: Fluoride
In simple words: Fluoride is the ingredient in toothpaste that helps protect teeth from decay.

🎯 Exam Tip: Recall the specific element added to toothpaste for cavity prevention.

Question 3. The property of a substance of spreading on a surface is called ................. .
Answer: surface activity
In simple words: The ability of a substance to spread out easily on a surface is known as surface activity.

🎯 Exam Tip: Define the term that describes a substance's ability to spread and wet surfaces efficiently.

Question 4. ................. and ................. are the natural detergent in common use.
Answer: Soap nut, Soap pod
In simple words: Soap nut and soap pod are commonly used natural detergents derived from plants.

🎯 Exam Tip: Name two common plant-based materials traditionally used as natural cleaning agents.

Question 5. Soap nut and soap pod contain a chemical named ................. .
Answer: Saponin
In simple words: The chemical responsible for the cleansing properties in soap nut and soap pod is saponin.

🎯 Exam Tip: Identify the specific chemical compound found in natural detergents like soap nut and soap pod.

Question 6. ................. is a man-made detergent.
Answer: Soap
In simple words: Soap is an example of a detergent that is created by human manufacturing processes.

🎯 Exam Tip: Recognize soap as a prime example of a detergent created through human synthesis.

Question 7. ................. is used for washing clothes.
Answer: Hard soap
In simple words: Hard soap is typically used for washing clothes due to its stronger cleansing properties.

🎯 Exam Tip: Recall the type of soap commonly designated for laundry tasks.

Question 8. ................. is used for bathing.
Answer: Soft soap
In simple words: Soft soap, being milder, is commonly used for personal bathing.

🎯 Exam Tip: Identify the type of soap generally preferred for personal hygiene due to its gentleness.

Question 9. Hard soap is ................. salt of fatty acids.
Answer: Sodium
In simple words: Hard soap is chemically a sodium salt derived from fatty acids.

🎯 Exam Tip: Connect the "hard" characteristic of soap to its specific alkali metal component.

Question 10. Soft soap is ................. salt of fatty acids.
Answer: Potassium
In simple words: Soft soap is chemically a potassium salt derived from fatty acids.

🎯 Exam Tip: Connect the "soft" characteristic of soap to its specific alkali metal component.

Exercise Name The Following:

Question 1. A substance which is spread on a given surface and used for cleaning.
Answer: Surfactant
In simple words: A surfactant is a substance designed to spread on surfaces and assist in cleaning by reducing surface tension.

🎯 Exam Tip: Understand that substances facilitating spreading and cleaning are broadly called surfactants.

Question 2. A chemical contained in soap nut and pod.
Answer: Saponin
In simple words: Saponin is the active chemical found in soap nut and soap pod responsible for their natural detergent properties.

🎯 Exam Tip: Recall the specific active compound in natural cleaning agents like soap nut.

Question 3. An element which helps prevent tooth decay which is used in toothpastes.
Answer: Fluoride
In simple words: Fluoride is the element commonly added to toothpastes to help protect against tooth decay.

🎯 Exam Tip: Identify the mineral element known for its protective role in dental health when used in toothpaste.

Question 4. The latin word which means detergent.
Answer: Detergere
In simple words: The Latin root word for detergent is "Detergere."

🎯 Exam Tip: Know the etymological origin of the word "detergent."

Question 5. A cement used for construction purpose.
Answer: Portland cement
In simple words: Portland cement is a widely used type of cement for various construction applications.

🎯 Exam Tip: Recognize Portland cement as the standard and most common type of cement in modern construction.

Question 6. A mixture of cement, water, sand and gravel.
Answer: Concrete
In simple words: Concrete is the mixture formed when cement, water, sand, and gravel are combined and allowed to harden.

🎯 Exam Tip: Understand that the combination of cement, water, sand, and gravel forms concrete.

Question 7. A natural detergent.
Answer: Soap nut
In simple words: Soap nut is an example of a detergent found naturally, used for cleaning.

🎯 Exam Tip: Identify a common example of a detergent derived from natural sources.

Exercise Choose The Correct Option:

Question 1. Which one of these material grows on an animal
(cotton, rubber, wood, wool)
Answer: (d) Wool
In simple words: Wool is the only material among the given options that originates and grows on animals, typically sheep.

🎯 Exam Tip: Differentiate between plant-based, synthetic, and animal-derived materials to correctly identify the source.

Question 2. Which of these is man-made?
(oranges, apples, plastic bags, tomatoes)
Answer: (c) Plastic bags
In simple words: Oranges, apples, and tomatoes are natural products, while plastic bags are synthetically manufactured, making them man-made.

🎯 Exam Tip: Categorize the items as natural or manufactured to identify the man-made option.

Question 3. The statue is made from marble, marble is a ................. material.
(weak, elastic, man-made, natural)
Answer: (d) Natural
In simple words: Marble is a natural stone, a metamorphic rock, used in sculpting and construction.

🎯 Exam Tip: Classify common building and artistic materials based on their origin as natural or man-made.

Question 4. Toy Duck is made from plastic. Plastic is a ................. material.
(natural, man-made, raw, precious)
Answer: (b) Man-made
In simple words: Plastic is a synthetic material, entirely created through chemical processes by humans, not found in nature.

🎯 Exam Tip: Recognize plastic as a synthetic material, distinguishing it from naturally occurring substances.

Question 5. Which of these materials is natural?
(Nylon, Rock, Plastic, Polythene)
Answer: (b) Rock
In simple words: Among the options, rock is the only naturally occurring material; nylon, plastic, and polythene are synthetic.

🎯 Exam Tip: Identify natural materials by their direct extraction from the environment, in contrast to synthetic compounds.

Question 6. Which one of these is a natural material?
(Lemonade, Cola, Water, Ice cream)
Answer: (c) Water
In simple words: Water is a fundamental natural material; lemonade, cola, and ice cream are processed products.

🎯 Exam Tip: Distinguish between raw natural substances and processed food/drink items.

Question 7. The toy plane made from wood. Wood is a ................. material.
(man-made, natural, weak)
Answer: (b) Natural
In simple words: Wood is a natural material, derived directly from trees.

🎯 Exam Tip: Recognize wood as a natural, plant-derived material.

Question 8. Which one of these materials is natural?
(Nylon, cotton, polythene, polyesters)
Answer: (b) Cotton
In simple words: Cotton is a natural fiber derived from the cotton plant, whereas nylon, polythene, and polyesters are synthetic materials.

🎯 Exam Tip: Differentiate between natural fibers (like cotton) and synthetic fibers/polymers.

Exercise Match The Following:

Question 1.

Answer:

In simple words: This match links fluoride to tooth decay prevention, soap nut as a natural detergent, soap as a man-made detergent, cotton as a natural material, nylon as a man-made material, hard soap as a sodium salt of fatty acid, calcium carbonate as a main toothpaste ingredient, and soft soap as a potassium salt of fatty acid.

🎯 Exam Tip: Carefully match each item in Column A with its correct description or category in Column B, focusing on material properties, origins, and functions.

Find Out:

Exercise Answer The Following Questions:

Question 1. What is the source of the fluoride in a tooth paste or tooth powder?
Answer: A naturally occurring mineral found in tooth paste and drinking water. Sodium Fluoride (NaF) is the source of fluoride in toothpaste.
In simple words: The fluoride in toothpaste comes from naturally occurring minerals, primarily in the form of sodium fluoride (NaF), which is also found in drinking water.

🎯 Exam Tip: State that fluoride is derived from naturally occurring minerals, specifying Sodium Fluoride (NaF) as the common source in dental products.

Question 2. Note down all the information given on a tooth powder/toothpaste container or carton and discuss.
Answer:
1. The carton shows the name of the company and name of toothpaste and its contains all the ingredients present in toothpaste.
2. Licence No. of company, Regd. Trade Mark of Colgate-Palmolive Co- manufactured by Colgate-Palmolive (India) Ltd. Licenced user of Trade Mark made in India. Tooth paste contains 1000 ppm max of available fluoride when packed.
Expt. Date:
Batch No.:
3. Ingredients: Calcium carbonate, sorbitol, sodium lauryl sulphate, silica, sodium silicate flavour, sodium monoflouro phosphate, sodium bicarbonate, benzyl alcohol.
4. Direction for use: Brush thoroughly atleast twice a day.
5. Children under 6 years of age should have adult supervision and use only appropriate amount.
In simple words: Toothpaste packaging provides crucial information like company details, ingredients (e.g., fluoride, calcium carbonate), usage directions, and safety warnings for children. This ensures consumers are well-informed about the product.

🎯 Exam Tip: Students should focus on identifying the key categories of information found on product packaging, such as ingredients, manufacturer, and usage instructions, for full marks.

Question 3. Now a days why are the roads made of concrete?
Answer:
1. Concrete is prepared by mixing cement, limestone, sand, gravel, and water. It is solid, more durable and strong.
2. There is no erosion for many years and roads are smoother. So the roads are made of concrete.
In simple words: Roads are now made of concrete because it's a very durable and strong mixture of cement, sand, gravel, and water. This construction leads to smooth roads that resist erosion for a long time.

🎯 Exam Tip: Emphasize the durability, strength, smoothness, and erosion resistance of concrete as the primary reasons for its use in modern road construction.

Question 4. What causes the hardness of water?
Answer:
1. Hardness is a measure of amount of dissolved salts in water.
2. It is caused by dissolved salts like carbonates, chlorides mostly of calcium and magnesium
3. Presence of these makes washing of clothes by soap difficult.
4. Hard water is water that has high mineral content.
5. Hard water is formed when water percolates through deposits of limestone and chalk.
In simple words: Water hardness is due to high levels of dissolved mineral salts, mainly calcium and magnesium carbonates and chlorides, which makes it difficult for soap to lather and clean effectively.

🎯 Exam Tip: Clearly state that dissolved calcium and magnesium salts (carbonates and chlorides) are the main culprits behind water hardness, affecting soap's cleansing action.

Can You Tell?

Question 1. Which substances were used earlier for cleaning teeth?
Answer: In olden times neem twigs, coal powder ash, tooth powder, salt, pomegranate rind, were used for cleaning teeth.
In simple words: Historically, people used natural items like neem twigs, coal ash, salt, and pomegranate rind to clean their teeth.

🎯 Exam Tip: List at least 3-4 historical methods or substances used for dental hygiene to score well.

Question 2. What do we use today to clean our teeth?
Answer: Now a days we use variety of toothpastes and tooth powders to clean our teeth.
In simple words: Currently, we primarily use various toothpastes and tooth powders for daily dental cleaning.

🎯 Exam Tip: A straightforward answer highlighting modern dental cleaning agents like toothpastes and tooth powders is sufficient.

Question 3. What do we use for cleansing our body?
Answer: Soap, many liquid body wash are also used to clean our body.
In simple words: For body cleansing, we use soap and increasingly, liquid body washes.

🎯 Exam Tip: Mention both traditional soap and modern liquid body washes as common cleansing agents.

Question 4. What are the materials used for construction?
Answer: Metals, wood, stone, cement, concrete, timber, bricks, metal sheet, soil, Earth, marble, aluminium, iron, steel, bamboo, glass, plastic. Concrete: is a wet mixture of sand, gravel, cement, and water used to create building foundations, footpaths or roads.
In simple words: Many materials are used for construction, including natural resources like wood, stone, and soil, as well as manufactured ones like cement, concrete (a mix of cement, sand, gravel, water), metals, bricks, glass, and plastic.

🎯 Exam Tip: Provide a comprehensive list of diverse construction materials, differentiating between natural and manufactured options where possible.

Question 5. Which of the houses seen in the pictures here have a strong structure? Why?
Answer:
ℹ️ चित्र व्याख्या (Diagram Explanation): इस चित्र में तीन प्रकार के घर दिखाए गए हैं - मिट्टी और पुआल से बने कच्चे घर, घास-फूस की छत वाली झोपड़ी, और पत्थर, ईंट व सीमेंट से बना आधुनिक पक्का घर। यह चित्र विभिन्न निर्माण सामग्रियों और उनसे बनी आवास संरचनाओं को दर्शाता है।
The houses made from stone, bricks, and cement and concrete have a strong structure.
In simple words: The houses built with stone, bricks, cement, and concrete have strong structures because these materials are durable and provide stability.

🎯 Exam Tip: Identify the specific materials (stone, bricks, cement, concrete) that contribute to a strong house structure and briefly explain why (durability, stability).

Write Short Notes On Or Explain:

Question 1. Natural detergent
Answer:
1. It is naturally available soap nut (ritha) and soap pod (shikekai) are the natural detergents in common use.
2. They contain a chemical named saponin.
3. Soap nut and soap pod do not have any harmful effect on human skin or on silk, woollen threads, and cloth.
In simple words: Natural detergents like soap nut (ritha) and soap pod (shikekai) are derived from plants, contain saponin, and are gentle on skin and delicate fabrics.

🎯 Exam Tip: Define natural detergents by listing examples (ritha, shikekai), mentioning their active component (saponin), and highlighting their mildness.

Question 2. Man-made detergents
Answer:
1. Detergent which is made by processing naturally available material, soap is a man-made detergent which has been in use since ancient times.
2. In those days soap was prepared by using animal fat and wood ash.
In simple words: Man-made detergents, such as soap, have been used for a long time and are produced by processing natural materials, historically from animal fat and wood ash.

🎯 Exam Tip: Explain that man-made detergents are processed from natural materials and provide historical examples of their composition (animal fat, wood ash).

Question 3. Soap
Answer:
Two types of soap are:
1. Hard soap is used for washing clothes. It is a sodium salt of fatty acids.
2. (a) Softsoap is used for bathing. It is a potassium salt of fatty acids, (b) It does not cause irritation of the skin, (c) But we can't use soap in hard water because soap does not give lather but forms a scum, (d) So, soap loses its cleansing property so now synthetic detergents have taken the place of soap, (e) Synthetic detergents are obtained by subjecting these raw materials (fats and kerosene) to a variety of chemical processes, (f) These can be used in hard water as well.
In simple words: Soap comes in two main types: hard soap (sodium salt of fatty acids) for washing clothes, and soft soap (potassium salt of fatty acids) for bathing. While soft soap is gentle on skin, traditional soaps struggle in hard water, leading to the rise of synthetic detergents.

🎯 Exam Tip: Differentiate between hard and soft soaps based on their chemical composition (sodium vs. potassium salts of fatty acids) and usage, and note the limitation of soap in hard water.

Question 4. Concrete
Answer:
1. Concrete is prepared by mixing cement, water, sand and gravel.
2. For making a strong and leak proof slab certain substances are mixed in concrete.
3. Now a days, roads are made of concrete because they are very durable, strong and smooth.
In simple words: Concrete is a strong construction material made from cement, water, sand, and gravel. It's used for durable, leak-proof slabs and smooth roads due to its strength and longevity.

🎯 Exam Tip: Describe concrete's composition (cement, water, sand, gravel) and its key properties like strength, durability, and smoothness, especially in road construction.

Question 5. Surface activity
Answer:
1. Soap molecule has the property of holding on to both oil and water soap water spreads easily on many types of surfaces.
2. The property of a substance of spreading on a surface is called surface activity and the substance is said to be a surfactant.
3. Detergents are surface-active. One effect of surface activity is lather formation.
In simple words: Surface activity is the ability of a substance, like soap, to spread easily on surfaces by interacting with both oil and water, reducing surface tension and leading to effects like lather formation. Substances with this property are called surfactants.

🎯 Exam Tip: Define surface activity as the spreading property of a substance (surfactant) due to its interaction with both oil and water, and connect it to lather formation.

Question 6. Explain the method of preparation of soap.
Answer:
Material required for preparation soap are 15 g sodium hydroxide, 60 ml coconut oil, 15 g salt, perfume, a glass rod, beaker, tripod, wire gauze, burner, water mould etc.
Procedure:
1. Take 60 ml of coconut oil in a beaker.
2. Dissolve 15 g sodium hydroxide in 50 ml water. Mix the sodium hydroxide solution in the oil slowly, while stirring with a glass rod.
3. Heat the mixture, and boil it for 10-12 minutes, stirring it all the while.
4. Take care that the mixture does not boil over while heating.
5. Dissolve 15 g salt in 200 ml water, pour this solution into the above mixture and stir.
6. The soap formed by the chemical reaction now floats on the water. After some time, it becomes thick.
7. Now separate the thick soap and add the perfume to it, shape the bar of soap using the mould.
8. In this process, fat and alkali combine to form salts of fatty acids.
9. Chemically, soap is a sodium or potassium salt 4 of fatty acids.
In simple words: Soap is made by combining coconut oil with a sodium hydroxide solution under heat and stirring. Salt is then added to separate the soap, which is then shaped and perfumed, chemically forming fatty acid salts.

🎯 Exam Tip: Detail the saponification process by listing key ingredients (oil, sodium hydroxide, salt), outlining the steps (mixing, heating, separation), and stating the chemical outcome (formation of fatty acid salts).