Class 7th Science

  1. State differences between acids and bases. Solution: Acids Bases Acids are sour in taste Bases are bitter in taste Acids turn blue litmus paper into red color The base does not change the colour of blue litmus paper Acids does not change the colour of the red litmus Bases turn red litmus paper to blue color Acids do not change the colour of turmeric Bases turn turmeric to red 2. Ammonia is found in many household products, such as window cleaners. It turns red litmus blue. What is its nature? Solution: The answer is basic in nature 3. Name the source from which litmus solution is obtained. What is the use of this solution? Solution: Litmus solution is extracted from lichens. Litmus solution is used as an indicator to find acidic and basic nature of a solution. 4. Is the distilled water acidic/basic/neutral? How would you verify it? Solution: Distilled water is neutral in nature, and this can be tested by using red and blue litmus paper. In either of the cases, colour remains uncha

  Acids An  acid  is a chemical substance that has a sour taste. Many food items such as lemons, curd, vinegar and orange taste sour because of the presence of acid in them. Acidic Substances  are the substances that contain acid in them. Natural Acids  are the acids that occur in nature, for example, acids found in fruits are natural acids. Bases A  base  is a chemical substance that has a bitter taste and a soapy texture. Bases are found in different substances such as bleach, ammonia, washing powder and soap. Bases are also called  Alkaline . Basic Substances  are the substances that contain a base in them. Figure 1: Acids and Bases found in Nature Neutral Substance  is any substance which is neither acidic nor basic in nature. Indicators We cannot taste every object and find its nature. Therefore, we use indicators. An indicator is a substance that can determine if another substance is acidic or basic in nature. The indicators indicate the presence of an acid or base in a substance