Acids, Bases And Salts, Class 7th Notes

THESE NOTES ARE PREPARED ACCORDING TO JKBOSE SYLLABI IN SIMPLIFIED AND CONCISE PATTERN

Exercises

I. Fill in the blank spaces by choosing correct words from the list given below:

List: bitter, ants, corrosive, citric, soapy, slaked lime.

1. The acid found in lemons is CITRIC acid.

2. The bases have a BITTER taste and SOAPY touch.

3. The sting of the ANTS contains formic acid.

4. Sulphuric acid is highly CORROSIVE acid.

5. Acidic soils are neutralized with   SLAKED LIME


II. Statements given below are incorrect. Write the correct statements.

1. Sulphuric acid is an example of an organic acid.

Ans: Sulphuric acid is an example of Mineral acid


2. Blue litmus paper turns red in a basic solution.

Ans: Blue litmus paper turns red in an Acidic solution


3. China rose solution turns green in citric acid solution.

Ans: China rose solution turns dark pink in citric acid solution

4. Formic acid is found in the sting of a grasshopper.

Ans: Formic acid is found in the sting of an Ant

5. During neutralization, an acid reacts with a salt to from water and a base, as products.

Ans: During neutralization, an acid reacts with Base to form water and Salt,  as products


III. Write true or false infront of the following statements:

1. Tooth decay is caused by the presence of basic substance in mouth:: False


2. The substance which shows different colours in acids and bases are called indicators:: True


3. Milk of magnesia and slaked lime are the examples of neutral substances :: False


4. Acid rain is caused by the excess of carbon dioxide in air:: False


5. Potassium hydroxide turns blue litmus red:: False


6.  Most of the fruits contain organic acids:: True


Answer the following questions:


1. Name three organic and three inorganic acids.

Ans:
The acids found in animals and plants are organic acids e.g; Citric acid, Tartaric acid, Lactic acid, Acetic acid.

The acids prepared from minerals by chemical means are inorganic acids e.g Sulphuric acid, Nitric acid, Hydrochloric acid.


2. What are indicators? Name any three indicators and state the colour change which takes place in (i) acids  (ii) bases.

Ans: Indicators are complex substances which change their colour on contact with acids or bases.

Examples:
                            Acid                  Base
Litmus:                 Red                Blue
China Rose:        Dark pink      Green
Phenolpthalein:  No change     Pink




3. What are neutral substances?Give examples of two neutral substances.

Ans: Neutral substances are those substances which are neither acidic nor basic.
They are former when acids react with bases.

Examples: Sodium chloride, Ammonium chloride, Pottasium chloride.



4. You are given three unlabelled bottles A, B and C, containing colourless solutions, such that one of them is acid, the other being basic and neutral respectively. How will you distinguish between them by using china rose as an indicator.

Ans:
When we pour china rose solution in bottle containing Acid, its colour will change to Dark Pink. 

When we pour china rose solution in bottle containing base, its colour will change to Green. 

When we pour china rose solution in bottle containing neutral substance, its colour will not change. 

5. What do you understand by the term neutralisation? Describe an activity in which neutralisation of hydrochloric acid takes place with sodium hydroxide, using phenolphthalein as an indicator.

Ans: Neutralization is a chemical reaction in which acid reacts with base to form salt and water.

In this reaction, evolution of heat takes place.

Activity:

Take sodium hydroxide solution in the beaker.
Add few drops of phenolpthalein indicator till the colour changes to Pink.
Now add hydrochloric acid into the solution drop by drop.
You will notice, that the solution suddenly becomes colourless.
It is because neutralization reaction takes place inside the solution. 

HCl + NaOH  ----> NaCl  + H2O   + Heat

6. Explain why:

(a) Farmers add slaked lime to acidic soils.

Ans: Acidic soils are formed due to excessive use of fertilizers and become less fertile.

Farmers add slaked lime to the acidic soils to make the soils neutral.


(b) Soap solution or baking soda paste is applied on the part of body stung by a bee.

Ans: Bee sting contains formic acid. We apply soap solution or baking soda to bee sting ti neutralize the effect of acid.

It helps in relieving pain.

(c) Factory wastes and city sewerage is neutralised before discharging in rivers.

Ans: Factory wastes and city sewerage contains many acids. If these wastes are directly discharged into rivers, it will kill living organisms there.

Hence, they are neutralized before discharging.


(d) Antacids are used for relieving stomach activity.

Ans: Antacids like milk of magnesia neutralize the effect of excess hydrochloric acid and help in relieving stomach acidity.


7. Give four differences between the acids and the alkalis.

Ans: The differences between acids and alkalies are given below: 

8. Write an equation when hydrochloric acid neutralises sodium hydroxide.

Ans:

HCl  +      NaOH ---->  NaCl   +  H2O  + Heat
Hydch acid sodium hydroxide  sodium chloride   water




MCQs: Choose the correct answer:

1. Name the acid which is present in the sting of ants:
(a) Acetic acid  (b) Formic acid

 (c) Oxalic acid   (d) Tartaric acid

Ans:  b. Formic acid

2. Blue litmus turns red in which solution:

(a) Acidic solution (b) Basic solution (c) Both acidic and basic solutions 

(d) Neutral solution


Ans: a. Acidic solution


3.  Which of the following is not a mineral acid?

(a) Hydrochloric acid (b) Sulphuric acid
(c) Citric acid              (d) Nitric   acid

Ans: c. Citric acid 


4. When few drops of china rose solution is added to shampoo taken in test tube the colour of the solution becomes:

(a)Blue (b) Red (c) Green (d) Deep Pink

Ans: d. Deep Pink

Explanation: Shampoos are acidic in nature. Its pH ranges from 3.5 to 5.5.





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