NCERT Solutions for Class 7 Science Chapter 5 - Acids, Bases, And Salts

Answer:

The correct way of making a solution of acid is water is to add acid to water as this reaction produces a small amount of heat and can be carried out safely. But , if we add water to acid , the reaction is highly exothermic and produces a large amount of heat and hence , can lead to explosion. Therefore , adding acid to water is the correct way of making a solution of acid in water.

Hence, the correct answer is option (b).
 

Answer:

Neutralization reaction can be defined as a reaction in which an acid and a base react together to form salt and water as products.
Therefore , the products of neutralization reaction are always salt and water.

Hence, the correct answer is option (c).

 

Answer:

Turmeric paste is yellow in colour. It does not change its colour in acidic solution and remains yellow. Whereas, it is converted to red in basic solution.

Hence, the correct answer is option (b).
 

Answer:

Phenolphthalein indicator is colourless in nature but it gives pink colour in a basic solution and remains colourless in an acidic solution.

Hence, the correct answer is option (d).

Answer:

When the soil is too basic, organic matter is added to it. Organic matter releases acids which neutralises the basic nature of the soil and improves its quality and growth.

Hence, the correct answer is option (a).

 

Answer:

Litmus is extracted from different species of 'lichens'. Litmus solution or litmus paper is commonly used to test whether the solution is acidic or basic in nature.

Hence, the correct answer is option (c).

Answer:

Neutralization reaction is a chemical reaction in which acid and base react together and form salt and water as products. It is an irreversible change. Hence, it is a chemical change that cannot be reversed.
Hence, the correct answer is option (d).
 

Answer:

When colour of the solution changes from yellow to red by a turmeric indicator, then, the solution is known as a basic solution.

Hence, the correct answer is option (a).

 

Answer:

Curd contains lactic acid and vinegar contains acetic acid. Therefore, the substances containing acids are curd and vinegar.
 
Hence, the correct answer is option (d).

Answer:

Phenolphthalein indicator gives pink colour in basic solution but remains colourless in acidic and neutral solutions.

Hence, the correct answer is option (c).
 

Answer:

Turmeric is an acid-base indicator as it remains yellow in acidic solution whereas it turns red in a basic solution.

Hence, the correct answer is option (c).
 

Answer:

Sodium chloride is soluble in water and hence, remains in solution form. On evaporation of this solution, water will get converted to vapour form and solid sodium chloride can be obtained. Hence, we can use the method of evaporation to obtain sodium chloride in solid form.

Answer:

(a) False -Substances can be either acidic, basic or neutral in nature.
(b) False -Acids do not turn all indicators red.
(c) True
(d) False - Common salt dissolved in water is a neutral solution and hence , colour of litmus paper will not change.
(e) False - Phenolphthalein is a synthetic indicator.
(f) True
(g) False -Lemon water is acidic in nature.

 

Answer:

Indigestion is caused by excess acid in the stomach. Also, orange juice is acidic in nature. Giving orange juice in a condition of indigestion will make the situation worse as the concentration of acid in stomach further increases. For curing indigestion, a base like antacid should be given to neutralize the excess acid in the stomach. Hence, it is not advisable to give her orange juice in this condition. 
 

Answer:

Answer:

Wasp releases a liquid substance in body when it sting. This liquid is alkaline in nature. Applying lemon juice as a remedy neutralizes the alkaline nature of the liquid released by wasp and will help to eliminate the pain. Whereas, applying baking soda will increase the pain and redness. Hence, applying lemon juice on wasp sting is an appropriate remedy.

Answer:

The sentence using these words will be:

The effect of an ant bite can be neutralized by rubbing moist baking soda.

Answer:

The correct match of  substances in column I with those in column II is shown below:

$$\begin{gathered} \left(a\right)\to \left(iii\right) \\ \left(b\right)\to \left(v\right) \\ \left(c\right)\to \left(iv\right) \\ \left(d\right)\to \left(i\right) \\ \left(e\right)\to \left(ii\right) \end{gathered}$$

 

Answer:

(a) Lemon juice and vinegar taste sour because they contain acids .
(b) Turmeric and litmus are natural acid-base indicators.
(c) Phenolphthalein gives pink colour with lime water.
(d) When an acidic solution is mixed with a basic solution, they neutralize each other forming salt and water.

Answer:

China rose is an indicator that turns acidic solutions to a dark pink colour and basic solutions to green colour.

• When Boojho added two drops of solution 'A' in his test tube , he got a dark pink colour. This means that solution 'A' is an acidic solution.
• When Paheli added 2 drops of solution 'B' to her test tube , she got a green colour. This means that solution 'B' is a basic solution as the china rose solution turns green on addition of a base.
• When Golu added 2 drops of solution 'C' , he did not get any change in the colour. This implies that solution 'C' is a neutral solution as neutral solutions show no change in colour.

Answer:

Across
(2) Neutral
(4) Basic
(7) Red

Down
(1) Indicator
(3) Turmeric
(5) Acidic
(6) Heat
 

Answer:

The suggested remedies for neutralization of the soil are:

• If the soil is too acidic, it should be treated with bases such as quick lime( calcium oxide) or slaked lime (calcium hydroxide) which can neutralize the excess acid in the soil.
• If the soil is too basic , organic matter should be added to it. Organic matter releases acids which neutralize the basic nature of the soil.

Answer:

Litmus solution can be used to identify the nature of each solution whether it is acidic/basic/neutral.

The activity can be performed as follows:

Add the blue litmus solution and then the red litmus solution into the test tubes containing sugar solution, baking soda solution , tamarind solution and salt solution. The colour changes in the solutions can be used to identify the nature of the solution.
The following changes are observed:

• Sugar and salt solution show no change in colour and hence , they are neutral in nature.
• Baking soda turns red litmus to blue which shows that it is basic in nature.
• Tamarind solution turns blue litmus solution to red which shows that it is acidic in nature.

Answer:

(a) When a piece of blue litmus paper is added in all the test tubes 'A','B' and 'C' then:
In test tube 'A' , blue litmus turns to red as tartaric acid is acidic in nature.
In test tube 'B' , blue litmus remains blue as soap solution is basic in nature , so, no change observed.
in test tube 'C' , blue litmus remains blue as pure water is neutral in nature.

(b)When a piece of red litmus paper is added in all the test tubes 'A','B' and 'C' then:
In test tube 'A' , red litmus remains red as tartaric acid is acidic in nature , so , no colour change observed.
In test tube 'B' , red litmus turns to blue as soap solution is basic in nature.
In test tube 'C' , red litmus remains red as pure water is neutral in nature.

(c)When a few drops of phenolphthalein solution is added to each test tube , then:
In test tube 'A' , solution remains colourless as tartaric acid is acidic in nature.
In test tube 'B', solution turns pink on addition of phenolphthalein as soap solution is basic in nature.
In test tube 'C', solution remains colourless as pure water is neutral in nature.



 

Answer:

(a) Since factory waste is disposed off in the river, it can kill the fish because factory waste consists of acids and other toxic chemicals which are harmful for aquatic life.
(b) If the factory waste is acidic in nature, it can be neutralized using basic substances such as quick lime or slaked lime.

Answer:

The two neutralization reactions related to daily life situation are:

(a) Ant's sting : Ant's sting releases formic acid into the skin. It can be neutralized by rubbing moist baking soda or putting calamine lotion because they are basic in nature.

(b) Acidity : Due to indigestion, too much acid is produced in the stomach that leads to acidity. This can be controlled by taking antacids like milk of magnesia which neutralises the effect of excessive acid..