I. Let us recall tastes of some edible substances listed in Table 5.1. If you have not tasted any of these substances taste it now and enter the result in Table 5.1 .
Substance Taste (sour/bitter/any other)
Lemon juice sour
Orange juice sour
Vinegar sour
Curd sour
Tamarind sour
Sugar sweet
Common salt salty
Amla sour
Baking soda bitter
Grapes sour
Unripe mango sour
II. Natural indicators around us : (Table 5.2)
| Sr. No | Test solution | Effect on red Litmus paper | Effect on blue litmus paper | Inference |
| 1. | Lemon juice | No change | Turns red | Acidic |
| 2. | Tap water | No change | No change | Neutral |
| 3. | Detergent solution | Turns blue | No change | Basic |
| 4. | Aerated drink | Turns blue | No change | Basic |
| 5. | Soap solution | Turns blue | No change | Basic |
| 6. | Shampoo | Turns blue | No change | Basic |
| 7. | Common salt solution | No change | No change | Neutral |
| 8. | Sugar solution | No change | No change | Neutral |
| 9. | Vinegar | No change | Turns red | Acidic |
| 10. | Baking soda solution | Turns blue | No change | Basic |
| 11. | Milk of magnesia | Turns blue | No change | Basic |
| 12. | Washing soda solution | Turns blue | No change | Basic |
| 13. | Lime water | Turns blue | No change | Basic |
Perform the given Activity :
Q1. What do you observe?
Ans: Turmeric paper turns red .
Table 5.3
| Sr.no | Test solution | Effect on turmeric solution | Remarks |
| 1. | Lemon juice | No change | Acidic/neutral |
| 2. | Orange juice | No change | Acidic/neutral |
| 3. | Vinegar | No change | Acidic/neutral |
| 4. | Milk of magnesia | Turns red | Basic |
| 5. | Baking soda | Turns red | Basic |
| 6. | Lime water | Turns red | Basic |
| 7. | Sugar | No change | Acidic/neutral |
| 8. | Common salt | No change | Acidic/neutral |
Perform the given activity :
Table 5.4
| Sr.no | Test solution | Initial colour | Final colour |
| 1. | Shampoo(dilute solution) | Pink | Green |
| 2. | Lemon juice | Pink | Magenta |
| 3. | Soda water | Pink | Green |
| 4. | Sodium hydrogen carbonate solution | Pink | Green |
| 5. | Vinegar | Pink | Magenta |
| 6. | Sugar solution | Pink | Pink |
| 7. | Common salt solution | Pink | Pink |
Q1. I am not getting the same result when using solid baking soda on dry litmus paper. Why?
Ans: In solid state ions of the substance are not free to move whereas in liquid state baking soda dissociates into ions and ions bring about colour change.
Q2. Paheli brought the following riddle for you :
i) Coffee is brown And bitter in taste Is it acid? Or a base? Don’t give the answer Without any test . You are in the dark With its taste .
Ans: Coffee is acidic in nature.
Perform the given Activity :
Table 5.5
| Sr.no | Name of acid | Effect on litmus paper | Effect on turmeric paper | Effect on china rose solution |
| 1. | Dilute Hydrochloric acid | Turns blue litmus red | No change | Magenta |
| 2. | Sulphuric acid | Turns blue litmus red | No change | Magenta |
| 3. | Nitric acid | Turns blue litmus red | No change | Magenta |
| 4. | Acetic acid | Turns blue litmus red | No change | Magenta |
| 5. | Sodium hydroxide | Turns red litmus blue | Red | Green |
| 6. | Ammonium hydroxide | Turns red litmus blue | Red | Green |
| 7. | Calcium hydroxide | Turns red litmus blue | Red | Green |
Perform the given activity : (State the colour change)
1. On adding 2 – 3 drops of phenolphthalein .
Ans: No change, colourless .
2. On adding a drop of sodium hydroxide solution .
Ans: No change, colourless .
TEXTUAL EXERCISES :
1. State the difference between acids and bases :
Acids Bases
1) Acids are sour in taste 1) Bases are bitter in taste
2) Turns blue litmus red 2) Turns red litmus blue .
2. 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.
3. Name the source from which litmus solution is obtained. What is the use of this solution .
Ans: Litmus is obtained from lichens. It is used an indicator.
4. Is the distilled water acidic/basic/neutral? How would you verify it?
Ans: Distilled water is neutral. It shows no colour change with red or blue litmus paper.
5. Describe 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.
Eg: HCI + NaOH NaCl + H2O .
6. Mark ‘T’ if the statement is true and ‘F’ if it is false.
i) Nitric acid turns red litmus blue. (T/F)
ii) Sodium hydroxide turns blue litmus red. (T/F)
iii) Sodium hydroxide and Hydrochloric acid neutralize each other and form salt and water. (T/F)
iv) Indicator is a substance which shows different colours in acidic and basic solutions. (T/F)
v) Tooth decay is caused by the presence of a base. (T/F)
Ans:
i) F ii) F iii) T iv) T v) F .
7. Dorji has a few bottles of soft drink in his restaurant. But unfortunately, these are not labelled. He has to serve the drinks on the demand of customers. One customer wants an acidic drink, another wants a basic and third one wants a neutral drink. How will Dorji decide which drink is to be served to whom.
Ans: Dorji can use an indicator to find out the nature of the drinks. If acidic it will turn blue litmus red, if basic it will turn red litmus blue, if neutral then there will be no colour change.
8. Explain why.
i) An antacid tablet is taken when you suffer from acidity.
Ans: The antacid tablet contains base magnesium hydroxide. It neutralizes the excessive acid produced in the stomach and hence used to relief from acidity.
ii) Calamine solution is applied on the skin when an ant bites.
Ans: When an ant bites, it injects formic acid into the skin calamine solution which is basic in nature, can neutralize the effect if the acid and bring relief to the person.
iii) Factory waste is neutralized before disposing it into the water bodies.
Ans: Factory waste is acidic in nature and can harm the aquatic life. Therefore it is neutralized with a base before releasing it into the water.
9. Three liquids are given to you. One is Hydrochloric acid, another is Sodium hydroxide and third is a sugar solution. How will you identify them? You have only turmeric indicator.
Ans: Turmeric indicator turns red on contact with a base. Take the first sample and add turmeric indicator, if it turns red it is a base. Add the second sample, if the colour changes to original yellow it is an acid as it neutralizes the base. If the colour remain red, it is sugar solution which is neutral.
10. Blue litmus paper is dipped in a solution. It remains blue. What is the nature of the solution? Explain .
Ans: The solution can be basic or neutral as both don’t have any effect on blue litmus paper.
11. Consider the following statements :
a) Both acids and bases change colour of all indicators.
b) If an indicator gives a colour change with an acid it does not give a change with a base.
c) If an indicator changes colour with a base, it does not change colour with an acid.
d) Changes of colour in an acid and a base depends on the type of the indicators.
Which of these statements are correct?
Ans:
i) All four ii) a and d iii) b and c iv) only d .