Acid Bases and Salts is Chapter 5 taken from JKBOSE and NCERT textbook of Science for students of Class 7th. In the previous post, I provided you with Questions and Answers for Chapter 4 Heat. This post is about Acid Bases and Salts Class 7th Question Answers. Before we move on to solutions you must have your basics clear. So, let me begin by giving you a brief overview of what you have studied in this chapter.
Acid Bases and Salts Class 7th Question Answers
Overview of Chapter
- ACIDS AND BASES.
- INDICATORS.
- NATURAL INDICATORS AROUND US.
- GENERAL PHYSICAL PROPERTIES OF ACIDS.
- GENERAL PHYSICAL PROPERTIES OF BASES.
- NEUTRALISATION.
- NEUTRALISATION IN EVERYDAY LIFE.
ACIDS AND BASES: The substances which are sour in taste and turn blue litmus to red are termed acids. Acids are of two types: Organic acids (Natural acids) and Mineral acids (Laboratory acids). The substances which are bitter in taste and turn red litmus to blue are termed bases. The substances which are neither acidic nor basic in nature are called neutral substances.
INDICATORS: An indicator is a substance or dye that changes the colour of a solution which contains acids and bases in it. Litmus, china rose indicator, turmeric, and phenolphthalein are some common indicators.
NATURAL INDICATORS AROUND US: The most common natural indicators around us are litmus, turmeric, china rose, and phenolphthalein.
- Litmus: Neutral litmus turns red in an acidic solution and it turns blue in a basic solution.
- Turmeric: It turns red in an acidic medium.
- China Rose: It turns deep pink in acidic solution and light green in basic solution.
- Phenolphthalein: It turns deep pink in basic solution and remains colourless in acidic and neutral solutions.
GENERAL PHYSICAL PROPERTIES OF ACIDS: Acids
- Are sour in taste.
- Turns blue litmus red.
- Are corrosive.
- Are soluble in water.
- Conducts electricity in their water solution.
GENERAL PHYSICAL PROPERTIES OF BASES: Bases
- Are bitter in taste.
- Turns blue litmus red.
- Like sodium hydroxide and calcium hydroxide.
- Are insoluble in water.
- Are slippery in touch.
NEUTRALISATION: Neutralisation is the reaction in which acid reacts with a base to form salt and water.
NEUTRALISATION IN EVERYDAY LIFE: There are some situations where neutralisation reaction plays an important role in our everyday life. These are indigestion, ant’s sting, soil treatment and waste treatment etc.
Exercises
(I) Fill in the blank spaces by choosing the correct words from the list given below:
bitter, ants, corrosive, citric, soapy, slaked lime.
- The acid found in lemons is citric
- The bases have a bitter taste and soapy
- The sting of the ants and bees contains formic acid.
- Sulphuric acid is a highly corrosive
- Acidic soils are neutralized with slaked lime or quick lime.
(II) Statements given below are incorrect. Write the correct statements.
- Sulphuric acid is an example of an organic acid.
- Blue litmus paper turns red in a basic solution.
- China rose solution turns green in citric acid solution.
- Formic acid is found in the sting of a grasshopper.
- During neutralization, an acid reacts with salt to form water and a base, as products.
Ans.
- Sulphuric acid is an example of a mineral acid.
- Blue litmus paper turns red in an acidic solution.
- China rose solution turns green in a basic solution like that of sodium hydroxide.
- Formic acid is found in the sting of ants and bees.
- During neutralisation, the acid reacts with a base to form salt and water.
(III) Write true or false in front of the following statements:
- Tooth decay is caused by the presence of a basic substance in the mouth. (False)
- The substance which shows different colours in acids and bases are called indicators. (True)
- Milk of magnesia and slaked lime are examples of neutral substances. (False)
- Acid rain is caused by the excess carbon dioxide in the air. (True)
- Potassium hydroxide turns blue litmus red. (False)
- Most fruits contain organic acids. (True)
Answer the following questions:
- Name three organic acids and three inorganic acids.
Ans. Three organic acids include citric acid, acetic acid, oxalic acid, malic acid and tartaric acid. Three inorganic acids include sulphuric acid, nitric acid, phosphoric acid, and carbonic acid etc.
- What are indicators? Name any three indicators and state the colour change which takes place in (i) acids (ii) bases.
Ans. Indicators are a special type of substance which are used to indicate whether a given substance is acidic or basic in nature.
| Name of indicator | Change in Colour | |
|---|---|---|
| Acids | Bases | |
| Litmus | Red | Blue |
| China Rose | Deep Pink (Magenta) | Green |
| Phenolphthalein | Colourless | Deep Pink |
- What are neutral substances? Give examples of two neutral substances.
Ans. The substances which are neither acidic nor basic in nature and do not affect indicators are termed neutral substances. Some examples of neutral substances are distilled water, common salt, oil, sugar solution, salt solution etc.
- 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. How will you distinguish between them by using the china rose as an indicator?
Ans. The solution can be distinguished in the following manner:
Add a few drops of china rose solution in all bottles A, B and C and observe them for some time to observe the colour change. The bottle in which there is no colour change has a neutral solution in it. The bottle in which the solution colour turns magenta (deep pink) has an acidic solution in it. The bottle in which the solution colour turns green has a basic solution in it.
- 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. Neutralisation is the process or reaction in which an acid reacts with a base to form salt and water along with the evolution of heat.
Activity:
- Take a small amount of sodium hydroxide solution, say 20-30 ml in a beaker.
- Using a dropper add drops of phenolphthalein solution to it till the colour of the solution turns deep pink.
- Now again using a dropper start adding drops of HCl to this pink solution of sodium hydroxide. Keep the solution stirring gently. After some time, we will find that after the addition of one drop of acid the solution becomes colourless. At this stage, the hydrochloric acid has been neutralised with sodium hydroxide to produce salt and water. Now, the last drop of HCl has made the solution acidic so the solution becomes colourless.
- Explain Why:
(a) Farmers add slaked lime to acidic soils.
Ans. Plants or crops grow well in neutral soil, when soil becomes acidic it reduces its fertility which in turn reduces the yield of the crops. So, to make the soil neutral in nature, farmers use slaked lime to it as slaked lime is basic in nature and will neutralise the effect of acids in the soil.
(b) Soap solution or baking soda paste is applied on the part of the body stung by a bee.
Ans. The sting of a bee has formic acid in it. When our body part is stung by a bee, it injects formic acid into our body. Formic acid causes irritation, pain and swelling in our body parts. We apply soap solution; baking soda paste to that part to reduce the effect of formic acid and help in relieving the pain.
(c) Factory wastes and city sewerage is neutralised before discharging in rivers.
Ans. Factory waste has acids in them. If this wasted is discharged as such to water bodies like rivers and lakes, it will make the water acidic which will harm the aquatic life of the water body and will cause the death of fish and other aquatic animals. To prevent this the factory wastes are treated with lime before being discharged into rivers which neutralises the effect of acids.
(d) Antacids are used for relieving stomach activity.
Ans. The release of excess HCl in our stomach causes indigestion or acidity. Antacid tablets or syrup is used to relieve the activity of the stomach because these contain the milk of magnesia (magnesium hydroxide or aluminium hydroxide). These hydroxides neutralise the effect of HCl and help in relieving acidity or stomach activity.
- Give four differences between the acids and the alkalis.
Ans. The four differences between acids and alkalis are as under:
| Acids | Alkalis (Bases) |
|---|---|
| They are sour in taste. | They are bitter in taste. |
| They turn blue litmus red | They turn red litmus blue |
| They are generally soluble in water | They are generally not soluble in water |
| They are not soapy in touch | They are soapy in touch |
| They turn china rose solution into deep pink. | They turn china rose solution green in colour |
- Write an equation for when hydrochloric acid neutralises sodium hydroxide.
MCQs: Choose the correct answer.
- 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.
- 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
- 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
- When a few drops of china rose solution is added to shampoo taken in a test tube the colour of the solution becomes:
(a) Blue
(b) Red
(c) Green
(d) Deep Pink
Ans. (c) Green
That’s all about Acid Bases and Salts Class 7th Question Answers. Hope it has helped you. Do share your views about this post in the comment section below:
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