Chapter Review:

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• Acids are sour substances which are found in curd, lemon juice, orange juice and in vinegar. 

• Substances like these which are bitter in taste and feel soapy on touching are known as bases. EX:- baking soda, soap and milk of magnesia.

• A special kind of substances are used to identify the acids and bases, these are called indicator.  

• A natural indicator is Litmus paper. 

• Such a solution which does not change the colour of red and blue litmus paper is called neutralised solution. 

• Such a reaction in which acid and base nutralise the effect of each other is known as neutralization.

• The food does not digest properly in our stomach due to excess of hydrochloric acid (acidity) this is known as indigestion. 

• A new substance is produced in neutralisation reaction is known as salt. 

• Acid turns blue litmus red. Bases turn red litmus blue.

Exercise 

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Q1. State differences between acids and bases.

Answer:

Acids are sour and turn blue litmus red .Bases are bitter and turn red litmus blue. 

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

Answer:

Basic.

Q3. Name the source from which litmus solution is obtained. What is the use of this solution?

Answer:

Lichens. It is a used as an indicator.

Q4. Is the distilled water acidic/basic/neutral? How would you verify it?

Answer:

Distilled water is neutral. 

Distilled water has no effect on blue as well as red litmus . So,it is neutral.

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

Answer:

The reaction between an acid and base is known as neutrallisation salt and water are produses in this process with the evolution of heat.

Q6. Mark ‘T’ if the statement is true and ‘F’ if it is false:

(i) Nitric acid turn red litmus blue. (T/F)

(ii) Sodium hydroxide turns blue litmus red. (T/F)

(iii) Sodium hydroxide and hydrochloric acid neutralise 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)

Answer:

(i) False (ii) False (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 drinks on the demand of customers. One customer wants acidic drink, another wants basic and third one wants neutral drink. How will Dorji decide which drink is to be served to whom?

Answer:

He can decide by the use of drink turns red litmus blue , it is basic. If it turns blue litmus red,it is acidic. If it does not affect litmus,it is neutral

Q8. Explain why:

(a) An antacid tablet is taken when you suffer from acidity. Keywords Acid Acidic Base Basic Indicator Neutral Neutralisation Salt ACIDS, BASES AND SALTS 57

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

(c) Factory waste is neutralised before disposing it into the water bodies.

Answer:

(a) Antacids tablet are basic in nature so, they neutralise the effect of excess acid in our stomach.

(b) calamine tablets are basic in nature so, they neutralise the effect excess ant bites.

(c) Factory waste contains acid which can harm, water animal and so, it is neutrallised before dispossing it into the water bodies. 

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:

Samples of the given three liquids are tested by adding a small quantity of turmeric to them. The liquid in which the coiour of turmeric changes from yellow to red ,is a base i.e.,sodium hydroxide solution .Then ,one of them remaining two unidentified solutions is added to it gradually. if the solutions turns yellow again, the added liquid is hydroxide acid.

Q10. Blue litmus paper is dipped in a solution. It remains blue. What is the nature of the solution? Explain.

Answer:

The solution may be neutral or basic. Both types of substance have no effect on blue litmus. 

Q11. 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) 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 d  (iii) b and c  (iv) only d

Answer:

(iv) only d.

Additional Question with solution:

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Ques: What are acids?
Ans: Acids are sour substances which are found in curd, lemon juice, and orange juice and in vinegar. 

Ques: What are base?
Ans: Substances like these which are bitter in taste and feel soapy on touching are known as bases. EX- baking soda, soap and milk of magnesia. 

Ques: Write the name of five such substances which are acidic in nature. 
Ans: curd, lemon juice, orange juice, tomato and vinegar etc. 

Ques: What is called the object which is used to identify the acids and bases? 
Ans: Indicator. 

Ques: Name a natural indicator?
Ans: Litmus paper. 

Ques: Write the type of litmus paper?
Ans: There are two types of litmus paper. 

(i) Red litmus paper 

(ii) Blue litmus paper 

Ques: From where does litmus paper obtain?
Ans: Litmus paper obtains from lichen plants. 

Ques: What is litmus paper?
Ans: Litmus paper is a natural indicator which is used to identify the acids and bases. 

Ques: What is indicator?
Ans: A special kind of substances are used to identify the acids and bases, these are called indicator. 

Ques: Which acid is found in vinegar?
Ans: Acetic acid. 

Ques: Which acid is found in ant’s sting?
Ans: Formic acid. 

Ques: Name the acid which is found in curd?
Ans: Lactic acid. 

Ques: What is called the neutralised solution?
Ans: Such a solution which does not change the colour of red and blue litmus paper is called neutralised solution. 

Ques: What is neutralisation?
Ans: Such a reaction in which acid and base nutralise the effect of each other is known as neutralization.

Ques: Write the difference between acid and base.
Ans: 

Acid:

(i) Acids are sour in taste.

(ii) It turns blue litmus into red.

(iii) Example: Hydrochloric acid. 

Base:

(i) Bases are bitter in taste.

(ii) It turns red litmus into blue. 

(iii) Example: Sodium hydroxide.

Ques: Why is dissolved baking soda applied on ant’s or scorpion’s sting?
Ans: There is a special kind of acid is found in the sting of ant and scorpion. So to neutralise the acid there is applied dissolved baking soda. 

Ques: What is indigestion?
Ans: The food does not digest properly in our stomach due to excess of hydrochloric acid (acidity) this is known as indigestion. 

Ques: What should we take to remove the indigestion?
Ans: We should take antacid like milk of magnesia to remove the indigestion. 

Ques: What is salt?
Ans: A new substance is produced in neutralisation reaction is known as salt. 

Ques: Write the nature of salt.

Ans: neutral. 

Ques: Why should it be taken great care while handling acid and base in laboratory? 

Ans: Great care should be taken while handling laboratory acids and bases because these are corrosive in nature, irritating and harmful to skin.

Ques: Name a synthetic indicator. 

Ans: Phenolphthalein.

Ques: What happens when acid and base react to each other? Write the equation for this.

Ans: When acid and base react to each other these give salt and water.
Equation: 
Acid + base -----> salt + water. 
Hydrochloric acid (HCl) + Sodium hydroxide (NaOH) -----> Sodium chloride (NaCl) + Water (H2O)

Ques: What is soil treatment? How is soil treated? 

Ans: When soil becomes too acidic or too basic, it is treated by using some acid or base substances. This is called soil treatment. When the soil is too acidic, it is treated with bases like quick lime (calcium oxide) or slaked lime (calcium hydroxide). If the soil is basic, organic matter is added to it. Organic matter releases acids which neutralises the basic nature of the soil.

Ques: How the factory wastages are harmful for aquatic animals?

Ans: The wastes of many factories contain acids. If they are allowed to flow into the water bodies, the acids will kill fish and other organisms.

Extra Question:

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Que: What is the testy for acids and bases using litmus paper?

Ans: Acids turn blue litmus paper red while bases turn red litmus paper blue. 

Que: What name is given to those to those substances which do not change the color of either red or blue litums paper?

Ans: The solutions or substances which do not change the color of either red or blue litmus paper are meutral.

Que: Write the name of two indicators which occur naturally?

Ans: 

• Turmeric
• China rose

Que: Name the acid present in lemon juice and tomato?

Ans: Citric acid in lemon juice and oxalic acid in tomato.

Que: Name a substance which is used to cure the discomfort caused by indigestion due to over eating?

Ans: Milk of magnesia which contains magnesium hydroxide is used to neutralise the effect of excessive acid in stomach.

Que: Is time water an acidic or basic solution?

Ans: Lime water is basic solution.

Que: Name the reaction when an acid is mixed with base.

Ans: Neutralisation reaction.

Que: Which acid is injected into our body an ant sting that causes pain?

Ans: The acid is formic acid which is injected into the skin of a person when an ant bites.

Que: Write twi basic substances which we use in our daily life?

Ans: 

• baking soda
• Soap or detergent

Que: Name one acid which is responsible for acid rain.

Ans: Carbonic acid.

Que: Why are sodium bicarbonate and lemon used during indigestion?

Ans: Sodium bicarbonate neutralises the acidity in the stomach. Hence, it is used during indigestion. Lemon contains acid. It reacts with undigested food and suffers it.

Que: How lime water is prepared in the laboratory?

Ans: To prepare lime water, disslove some lime in water in a bottle. Stir the solution and keep it for sometime. pour a little from the top. This is lime water.

Que: Which is an acid - base indicator?

Ans: Turmeric.