Topic outline

    • Acids, Bases and Salts

      Q1. Fill in the blanks.

                                 i.        Change of colour in an acid and a base depends on the type of the indicator.

                                ii.        Acid turns blue litmus red.

                               iii.        Bases turn red litmus blue.

                               iv.        Litmus has a mauve (purple) colour in distilled water.

                                v.        In neutralisation reaction a new substance is formed. This is called salt.

                               vi.        Lemon juice is acidic in nature.


      Q2. True/False

                                  i.        Nitric acid turns red litmus blue. False

                                 ii.        Sodium hydroxide turns blue litmus red. False

                                iii.        Sodium hydroxide and hydrochloric acid neutralise each other and form salt and water. True

                                iv.        Indicator is a substance which shows different colours in acidic and basic solutions. True

                                 v.        Tooth decay is caused by the presence of a base. False

                                vi.        If an indicator changes colour with a base, it does not change colour with an acid. False

      Q3. What is acid rain?

      Ans. The rain containing excess of acids is called an acid rain.


      Q4. Which acid naturally present in our stomach?

      Ans. Hydrochloric acid (HCl)


      Q5. What is the role of hydrochloric acid in the stomach?

      Ans. Hydrochloric acid (HCl) helps us to digest food.


      Q6. Which acid is present in an ant sting?

      Ans. Formic acid is present in an ant sting.


      Q7. What is the nature of soap solution?

      Ans. Soap solution is basic in nature.


      Q8. What is the nature of distilled water?

      Ans. The Distilled water is neutral.

      Q9. State the nature of baking soda.

      Ans. Baking soda is basic in nature.

      Q10. Where does the word acid come from?

      Ans. The word acid comes from the Latin word acere which means sour.


      Q11. Why curd, lemon juice, orange juice and vinegar taste sour?

      Ans. These substances taste sour because they contain acids.


      Q12. Which is the most commonly used natural indicator?

      Ans. The most commonly used natural indicator is litmus.


      Q13. Tom rubs a solution between fingers and feels soapy, what is the nature of that solution?

      Ans. Basic


      Q14. Name the acid which is present in each cell of our body.

      Ans. Each cell in our body contains an acid, the deoxyribonucleic acid or DNA.


      Q15. When red litmus paper is dipped in a solution; it remains red, what is the nature of the solution?

      Ans. Neutral


      Q16. What are the effects of acid rain?

      Ans. Acid rain can cause damage to buildings, historical monuments, plants and animals.

      Q17. What does organic matter do in soil?

      Ans. If the soil is basic, organic matter is added to it. Organic matter releases acids which neutralises the basic nature of the soil.


      Q18. Why solid baking soda does not change colour of dry litmus paper?

      Ans. The solid baking soda does not change colour of dry litmus paper because in solid states ions are not free to move.


      Q19. How acidic soil can be treated?

      Ans. When the soil is too acidic, it is treated with bases like quick lime (calcium oxide) or slaked lime (calcium hydroxide).


      Q20. What are salts? Give example.

      Ans. In neutralisation reaction a new substance is formed. This is called salt. Salt may be acidic, basic or neutral in nature. Example: Sodium chloride.


      Q21. What is the role of DNA in the cell of the human body?

      Ans. It controls every feature of the body such as our looks, colour of our eyes, our height etc.


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