Maharashtra State Board Class 7 Science Material we use Notes / Textbook Exercises and Extra Question and Answers.
Class 7 Science Material we use Notes
Toothpaste:
- Principal ingredients: Calcium carbonate, calcium hydrogen phosphate.
- Functions: Remove dirt and polish teeth.
- Contains fluoride to prevent tooth decay and strengthen bones and tooth enamel.
Detergents:
- Detergent defined as “a substance that cleans or wipes away dirt.”
- Examples of natural detergents: Soap nut (ritha) and soap pod (shikekai) containing saponin.
- Man-made detergent: Soap invented about 2000 years ago, traditionally made from animal fat and wood ash.
- Types of soaps: Hard soap for washing clothes (sodium salt of fatty acids), soft soap for bathing (potassium salt of fatty acids).
- Soap doesn’t work well in hard water (forms scum).
Synthetic Detergents:
- Replaced traditional soap, can be used in hard water.
- Made from fats or kerosene through various chemical processes.
Cement Production:
- Cement is vital in construction, used to make concrete materials.
- Composition of Portland cement: 60% lime (calcium oxide), 25% silica (silicon dioxide), 5% alumina, iron oxide, and gypsum.
- Named after the Isle of Portland in England.
- Historical use of cement dates back to ancient Romans, lost knowledge revived by John Smeaton in 1756.
- Concrete is prepared by mixing cement, water, sand, and gravel for various construction applications.
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 materials is called detergent.
(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, Portland cement is the most commonly used cement.
