Topic outline

    • Acids, Bases and Salts

      Q22. Give examples of some acids and bases.

      Ans. Acids - Curd, lemon juice, vinegar, orange juice etc.

      Base - baking soda, lime water etc.


      Q23. What are indicators?

      Ans. Solutions of substances that show different colour in acidic, basic and neutral solutions are called indicators.


      Q24. What is the effect of the China rose indicator on acidic and basic solutions?

      Ans. China rose indicator turns acidic solutions to dark pink (magenta) and basic solutions to green.


      Q25. Ammonia is found in many household products, such as window cleaners. It turns red litmus blue. What is its nature?

      Ans. Ammonia is basic in nature as it turns the red litmus blue.


      Q26. Why a turmeric stain on my white shirt is turned to red when it is washed with soap.

      Ans. A turmeric stain on my white shirt is turned to red when it is washed with soap because the soap solution is basic in nature.

      Q27. How to prepare lime water?

      Ans. To prepare limewater, dissolve some lime (chuna) in water in a bottle. Stir the solution and keep it for some time. Pour a little from the top. This is lime water.


      Q28. Blue litmus paper is dipped in a solution. It remains blue. What is the nature of the solution? Explain.

      Ans. The solution could be a base or neutral solution because blue litmus paper doesn’t change its colour in the neutral as well as in basic solution.


      Q29. What do you mean by neutral solution? Give examples.

      Ans. The solutions which do not change the colour of either red or blue litmus are known as neutral solutions. Examples- sugar solution, distilled water, salt etc.


      Q30. Is the distilled water acidic/basic/neutral? How would you verify it?

      Ans. Distilled water is neutral in nature. This can be verified by using red and blue litmus papers. Neither will show change in colour with distilled water. This proves that distilled water is neutral.


      Q31. How does rain become acidic?

      Ans. The rain becomes acidic because carbon dioxide, sulphur dioxide and nitrogen dioxide (which are released into the air as pollutants) dissolve in rain drops to form carbonic acid, sulphuric acid and nitric acid respectively.

      Q32. Why factory waste is neutralised before disposing it into the water bodies?

      Ans. The wastes of many factories contain acids. If they are allowed to flow into the water bodies, the acids will kill fish and other organisms. The factory wastes are, therefore, neutralised by adding basic substances.


      Q33. Calamine solution is applied on the skin when an ant bites. Give reason.

      Ans. When an ant bites, it injects the acidic liquid (formic acid) into the skin. The effect of the acid can be neutralised by rubbing moist baking soda (sodium hydrogen carbonate) or calamine solution, which contains zinc carbonate.


      Q34. Name the source from which litmus solution is obtained. What is the use of this solution?

      Ans. Litmus solution is extracted from lichens. It is most commonly used natural indicator. It has a mauve (purple) colour in distilled water. When added to an acidic solution, it turns red and when added to a basic solution, it turns blue.


      Q35. Why we take an antacid tablet when we suffer from acidity?

      Ans. Our stomach contains hydrochloric acid. It helps us to digest food. But too much of acid in the stomach causes indigestion. Sometimes indigestion is painful. To relieve indigestion, we take an antacid such as milk of magnesia, which contains magnesium hydroxide. It neutralises the effect of excessive acid.


      Q36. Explain the process of neutralisation with the help of an example.

      Ans. The reaction between an acid and a base is known as neutralisation. Salt and water are produced in this process with the evolution of heat.

      Acid+Base Salt+Water

      (Heat is evolved)

      The following reaction is an example:


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