NCERT solution for class 7th //Science // Chapter 5 . Acid ,Bases and Salt

 NCERT solution > class 7th  > Science  

NCERT solution for class 7th  //Science  // Chapter 5 . Acid ,Bases and Salt

Chapter 5 . Acid , Bases and Salt

 Exercise 

Q1. State differences between acids and bases 

Answer - 

Q2. Ammonia is found in many household products such as window cleaners it turns red litmus blue what is its nature?

Answer -   

Ammonia is basic in nature and it turns the colour of red litmus paper into blue

Q3. Name the sources from which litmus solution is obtained what is the use of the solution ? 

Answer  

Litmus solution is obtained from a natural dye extracted from lichen is dissolved in distilled water and perform litmus solution 

Litmus identify both the solution acidic as well as basic in acidic solution it shows red colour while in basic solution is shows blue colour and in neutral solution there is no change

Q4. Is the distilled water acidic basic or neutral how would you verify it 

Answer  

Distilled water is neutral in nature and it can be identified with the help of litmus paper if the red and blue litmus paper are dipped in it respectively then it shows no colour change so it prove that is distilled water is neutral

Q5. Describe the process of neutralisation with the help of an example 

Answer . 

Acid and base react with each other they form salt and water and nutrify the effect of each other that reaction is called neutralization reaction 

Acid + base   → salt + water + heat 

NaOH + HCl   →  NaCl + H2O + Heat

Q6 . Mark T if the statement is true and if it is false .

i) Nitric acid turns red litmus blue 

ii) Sodium hydroxide turn blue litmus red 

iii) Sodium hydroxide and hydrochloric acid neutralize each other and form salt and water 

iv) Indicator is a substance which shows different colours in acidic and basic solution 

v) Tooth decay is caused by the presence of the base 

Answer  

i) false 

ii)  true 

iii)  true 

iv )  true  

v) false

Q7. Dorji has a few bottles of soft drink in his restaurant but unfortunately these are not labelled he has to serve the drink on the demand of customers one customer wants acidic drink another wants basic and third one wants neutral drink how will dhoraji decided which drink is to be served to whom 

Answer  

Dorji can use litmus indicator to identify the drink he put one drop of each drink on the blue litmus paper if it turns red then it is acidic drink and after that he put one drop of each drink  on red litmus paper if it turns blue means the drink is basic in nature and neutral drink does not shows any change in both the litmus paper 

He also can identify it to take a taste the acidic drink has sour taste while a basic drink has a bitter taste and the neutral drink does not will  have not any  taste 

Q8 . Explain why 

a) An antacid tablet is taken when you suffer from acidity 

b) Calamine solution is applied on the skin when an ant bites

c) Factory waste is neutralized before disposing it into the water bodies 

Answer  . 

a) During acidity an excess of acid is produced in a stomach and antacid contain base such as milk of magnesia these base react with excess of acid and neutralize the effect of it and rapidly gives us relief 

b) When ant bite it inject the formic acid into the skin and calamine solution contain a basic substance like a zinc carbonate if it is applied on affected area of  the skin it neutralize the effect of formic acid 

c) Most of the industrial waste is acidic in nature and it is very harmful for the aquatic organism if it is directly dump it the water bodies it may harm for aquatic lives so before disposing it in water bodies it is neutralize with basic chemicals

Q9 . 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 

Answer . 

If we put a drop of each solution in a turmeric indicator the basic solution turn it into red colour means it is Sodium hydroxide if again we put the Sodium hydroxide drop on other two liquid and then put it on turmeric indicator if it changed into red colour then it is sugar solution because it is neutral in nature. If Sodium hydroxide is added in the third solution and will not change the colour of turmeric indicator means it is hydrochloric acid because it reacts with sodium hydroxide and form a neutral solution

Q10 . Blue litmus paper is dipped in a solution it remains blue what is the nature of the solution explain ? 

Answer  

If blue litmus paper is dipped in a solution and it remains blue means in nature of the solution may be base or neutral because base turn red litmus to Blue but do not react with blue litmus while neutral substance also does not react with litmus solution

Q11. Consider the following statements 

a) Both acids and bases change colour of the 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 change colour with a base it does not change colour with an acid 

d) Change of colour in an acid and a base depends on the type of the indicator 

Which of these statements are correct 

i) all four     

ii) a and b   

iii) b c and d  

iv ) only d  

Answer 

iv ) Only d