Materials we Use | Class 7 | Science | Chapter 15 | Maharashtra State Board
Explore the fascinating world of everyday materials with our channel! Dive into the science behind toothpaste, soap, natural and synthetic detergents, cement, concrete, and more. Join us to discover how these common items are made, their uses, and their impact on our lives. Subscribe now to start your learning journey!
Questions & Answers
1. Fill appropriate terms in the blanks:
(white cement, soap, detergent, wearing of bones, tooth decay, hard, soft, Portland, fatty acid)
(a) The substance that helps water to remove dirt from the surface of material is called soap.
(b) Fluoride is used in toothpaste to prevent tooth decay.
(c) Soap is a salt of fatty acid and sodium hydroxide.
(d) Synthetic detergents can be used in hard water as well.
(e) For construction purposes white cement is the most commonly used cement.
2. Write the answers to the following questions.
(a) How does the use of a detergent help to clean soiled clothes ?
Ans. Detergents help clean soiled clothes by breaking down and removing dirt, grease, and stains. They contain surfactant molecules that surround and lift away particles from fabric. The hydrophobic (water-repelling) end of the surfactant attaches to grease and oil, while the hydrophilic (water-attracting) end allows these particles to be carried away by water during rinsing. This process helps to disperse and suspend dirt, making it easier to wash away, leaving your clothes clean.
(b) How will you check with the help of soap powder whether water is hard ?
Ans. To check if water is hard, mix a small amount of soap powder with the water. If the water is hard, you'll notice that the soap doesn't lather well and forms scum instead. In contrast, in soft water, soap lathers easily and doesn't produce scum.
(c) What are the important ingredients of a toothpaste , and what is the function of each ?
Ans. Important ingredients of toothpaste are:
1. Fluoride: Prevents tooth decay by strengthening tooth enamel.
2. Abrasive Agents (Calcium carbonate, Silica): Help remove plaque and surface stains.
3. Humectants (Glycerine, Sorbitol): Retain moisture, preventing the toothpaste from drying out.
4. Detergents (Sodium lauryl sulphate): Create foaming action for better distribution and cleaning.
5. Flavouring Agents (Peppermint, Spearmint): Provide a pleasant taste to encourage regular use.
6. Thickeners (Xanthan gum, Carrageenan): Give the toothpaste its texture and consistency.
7. Preservatives (Parabens, Benzoic acid): Extend the shelf life by preventing bacterial growth.
(d) What are the ingredients of cement ?
Ans. The primary ingredients of cement are:
1. Limestone (Calcium carbonate): Provides the main source of calcium.
2. Clay or shale: Contains silica, alumina, and iron oxide.
3. Silica sand: Adds silicon for strength.
4. Iron ore or mill scale: Provides iron.
5. Gypsum (Calcium sulphate): Regulates setting time and enhances workability.
(e) What will happen if cement is not used in making concrete ?
Ans. Without cement, concrete would lack the binding agent needed to hold the mixture together. Cement reacts with water to form a solid matrix, providing strength and durability to concrete. Without cement, the components (such as sand, gravel, and water) would not effectively bond, resulting in a weak and crumbly material that lacks structural integrity.
(f) Make a list of detergents that you use.
Ans. There are two types of detergents that we use, (a) Natural (b) Man-made detergents.
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.
• Detergents are commonly available as powders or concentrated solution.
• Detergents are for laundry, washing clothes and cleaning dishes.
4. Alkaline detergents used for hard surface cleaning.
(g) What should be expected from a detergent for delicate garments ?
Ans. A detergent for delicate garments should be mild, gentle, and free of harsh chemicals. It should effectively clean without causing damage or fading to delicate fabrics. Look for a detergent labelled as "gentle" or "delicate," as these are designed to maintain the integrity of fragile materials while still providing effective cleaning.
(h) What is meant by ‘surface activity’ ? Name three chemicals responsible for the surface activity of various detergents.
Ans. Surface activity refers to the ability of a substance to interact with the surface of another material. In the context of detergents, this involves the ability to reduce the surface tension of water and break down and lift away dirt. Three chemicals responsible for the surface activity of detergents are:
1. Surfactants (Surface-Active Agents)
2. Sodium lauryl
3. Alkyl benzene sulfonates
3. What are the similarities and differences between -
(a) Natural detergents and man-made detergents
Ans. Similarities:
1. Cleaning Function: Both natural and man-made detergents are designed to clean by removing dirt, grease, and stains from surfaces.
2. Surfactants: Both types contain surfactants, which are responsible for reducing the surface tension of water, aiding in the removal of dirt and oil.
Differences:
1. Source: Natural detergents are derived from plant or animal-based ingredients, while man-made detergents are synthesized from chemical compounds.
2. Biodegradability: Natural detergents tend to be more biodegradable and environmentally friendly compared to some synthetic detergents, which may contain non-biodegradable compounds.
3. Ingredients: Natural detergents often contain ingredients like soap, plant-based oils, and extracts. Man-made detergents use a variety of synthetic chemicals, including surfactants like sodium lauryl sulphate.
4. Effectiveness: Man-made detergents may be formulated for specific cleaning purposes and can sometimes be more effective in removing certain types of stains or soils.
5. Foaming: Natural detergents may produce less foam compared to some synthetic detergents, as the latter often include foaming agents for a perceived cleaning effect.
6. Scent: Natural detergents may have scents derived from essential oils, while synthetic detergents may use artificial fragrances.
(b) Soap and synthetic detergent
Ans. Similarities:
1. Cleaning Function: Both soap and detergents are used for cleaning by removing dirt, grease, and oils from surfaces.
2. Surfactants: Both contain surfactants, which reduce the surface tension of water and help in the removal of dirt and oil.
3. Water-soluble: Both are water-soluble and can be easily rinsed away with water.
Differences:
1. Source: Soap is typically made from natural ingredients such as fats or oils combined with an alkali (e.g., sodium hydroxide), while detergents are synthetic compounds often derived from petrochemicals.
2. Hard Water Reaction: Soap tends to form a scum in hard water (water with high mineral content), reducing its effectiveness. Detergents usually perform better in hard water.
3. Biodegradability: Soap is generally more biodegradable and environmentally friendly compared to many synthetic detergents.
4. Effectiveness in Hard Water: Detergents are generally more effective than soap in hard water because they do not react with minerals to form soap scum.
5. Sensitivity: Some people may be sensitive or allergic to certain ingredients in soaps, while detergents may be formulated to be less irritating.
6. Foaming: Soap tends to produce more foam than most detergents, which may affect its perception of cleaning effectiveness.
7. Usage: Soap is commonly used for personal care products, such as hand soap and body wash, while detergents are more prevalent in household cleaning products like laundry detergents and dishwashing liquids.
(c) Bath soap and soap for washing clothes
Ans. Similarities:
1. Cleaning Function: Both bath soap and laundry soap are designed to clean by removing dirt, oils, and stains from surfaces.
2. Surfactants: Both types of soap contain surfactants that help in the emulsification and removal of dirt and oils.
3. Water-soluble: Both are water-soluble and can be rinsed away easily with water.
Differences:
1. Ingredients: Bath soap is typically formulated with ingredients suitable for skin care, such as moisturizers and fragrances. Laundry soap is designed with a focus on removing stains and dirt from fabrics.
2. Surfactant Types: While both contain surfactants, the specific types may vary. Laundry soaps often have stronger surfactants to tackle tougher stains on fabrics.
3. Residue: Bath soap is formulated to leave a moisturizing residue on the skin, whereas laundry soap is designed to rinse away completely without leaving a residue on clothes.
4. Fragrance: Bath soaps often have pleasant fragrances for personal care, while laundry soaps may have a milder or no fragrance to avoid clashing with fabric softeners or dryer sheets.
5. pH Levels: Bath soaps are usually formulated to be more skin-friendly, with a pH closer to that of the skin. Laundry soaps may have a different pH to optimize fabric cleaning.
6. Packaging: Bath soaps are typically available in bars or liquid form for personal use, while laundry soaps are commonly found in powder or liquid form for use in washing machines.
(d) Modern cement and ancient cement
Ans. Similarities:
1. Basic Function: Both modern and ancient cement are used as binding materials in construction to create strong and durable structures.
2. Raw Materials: Both types involve the use of similar raw materials, such as limestone and clay, in varying proportions.
Differences:
1. Composition: Ancient cement, like Roman cement, was often made from a mixture of lime, volcanic ash, and chunks of pottery. Modern cement, such as Portland cement, has a different composition, typically involving limestone, clay, and other additives.
2. Production Technology: The manufacturing processes differ significantly. Ancient cement production methods relied on natural materials and mixing techniques, while modern cement production involves high-temperature kilns and advanced chemical processes.
3. Strength and Durability: Modern cement, especially Portland cement, generally offers higher compressive strength and durability compared to ancient cement varieties.
4. Setting Time: The setting time of ancient cement might have been longer, and the curing process was often gradual, whereas modern cement formulations allow for more controlled setting times.
5. Consistency: The manufacturing processes for modern cement provide a more consistent product, allowing for standardized construction practices. Ancient cement formulations and production methods could result in variations in quality and performance.
6. Application: Ancient cement was primarily used for specific construction purposes, such as in Roman structures. Modern cement is widely used in various construction applications globally.
7. Admixtures: Modern cement formulations often include admixtures for specific properties, such as accelerating or retarding setting times, improving workability, or enhancing durability. Ancient cement did not benefit from such additives.
4. Explain why -
(a) Soap cannot be used in hard water.
Ans. Soap reacts with minerals present in hard water, particularly calcium and magnesium ions, to form insoluble compounds known as soap scum. This reduces the effectiveness of the soap, making it less capable of producing lather and cleaning. Instead of forming a lather, soap combines with minerals to create a residue that can stick to surfaces, including fabrics, leaving them feeling less clean and possibly dingy. In hard water, the presence of these minerals interferes with the cleaning action of soap, making it less suitable for use compared to detergents in such water conditions.
(b) Oil does not mix in water. However, oil and water become homogeneous if a sufficient quantity of detergent is added.
Ans. Oil and water don't mix because they have different properties: oil is hydrophobic (repellent to water), and water is hydrophilic (attracts water). Detergents have special molecules called surfactants. One end of the surfactant is attracted to water, and the other end is attracted to oil. When you add detergent to oil and water, these surfactant molecules surround the oil droplets, forming tiny structures called micelles. The water-attracting parts face outward, while the oil-attracting parts face inward, creating a sort of protective shield around the oil droplets. This allows the oil and water to mix, forming a homogeneous solution, and making it easier to wash away the oil with water.
(c) Synthetic detergents are superior to soap.
Ans. Synthetic detergents are often considered superior to soap for several reasons:
1. Hard Water Tolerance: Synthetic detergents perform well in hard water, which contains high levels of minerals like calcium and magnesium. Soap tends to form scum in hard water, reducing its effectiveness, while synthetic detergents can work efficiently in both hard and soft water.
2. Rinsing: Soap leaves a soap scum residue that can be difficult to rinse off, especially in hard water. Synthetic detergents do not form this scum, making rinsing easier and leaving surfaces cleaner.
3. Effectiveness in Cold Water: Synthetic detergents are generally effective in cold water, whereas soap may not lather well or clean as effectively in colder temperatures.
4. Compatibility with Fabrics: Synthetic detergents are often formulated to be gentler on fabrics, reducing the likelihood of damage or fading compared to some soaps.
5. Versatility: Synthetic detergents can be formulated for specific purposes, such as laundry, dishwashing, or personal care. They can be tailored to address various cleaning needs more effectively than a standard soap.
6. Biodegradability: While some traditional soaps are biodegradable, certain synthetic detergents can also be formulated to be environmentally friendly, making them a sustainable choice.
(d) Often coloured spots are formed on clothes during washing.
Ans. Many common personal care and beauty products, as well as environmental factors, can contribute to stains and colour changes in clothes. Substances like toothpaste, perspiration, facial soap, deodorants, hair sprays, strong perfumes with alcohol, and even rain can leave stains or affect the colour of fabrics. Some stains may not be immediately visible but can become apparent over time due to factors like aging and exposure to heat.
(e) Tobacco masheri should not be used for cleaning teeth.
Ans. Using tobacco masheri for cleaning teeth is not recommended for several reasons:
Oral Health Risks: Tobacco contains harmful substances, including nicotine and tar, which can contribute to various oral health problems. Using tobacco masheri for cleaning teeth can lead to stained teeth, bad breath, and an increased risk of gum disease and tooth decay.
Cancer Risk: Tobacco use, including its application in dental cleaning, is associated with an increased risk of oral cancer. The chemicals in tobacco can be damaging to the soft tissues in the mouth and may contribute to the development of cancerous lesions.
Addiction Potential: Tobacco is an addictive substance, and using it in any form, even for dental cleaning, can contribute to the development of addiction and dependence on nicotine.
Note: If you have any additional questions or feedback, please leave them in the comment section below. We will try to answer them and update this blog accordingly as soon as possible.