These AP 7th Class Science Important Questions and 4th Lesson Acids Bases and Salts Class 7 Extra Questions will help students prepare well for the exams.
Class 7 Science Acids Bases and Salts Extra Questions
Acids Bases and Salts Class 7 Important Questions
Question 1.
What are acids?
Answer:
The chemical compounds which are sour in taste are called acids. Examples: Lemon juice, curd, vinegar etc.
Question 2.
What are bases ?
Answer:
The substances which are bitter in taste and feel soapy on touching are known as bases. Examples : Baking soda, lime water etc.
Question 3.
Look at the given reaction.
Hydrochloric acid + Sodium hydroxide (base) → Sodium chloride (salt) + Water Sodium chloride formed in this reaction remains in solution form. Can we get solid sodium chloride from this solution? Suggest a method (if any).
Answer:
Sodium chloride is soluble in water hence a solution of sodium chloride in water is formed. Sodium chloride can be separated from this solution by evaporation.
Question 4.
Define indicators along with examples.
Answer:
The special type of substances which are used to test whether a substance is acidic or basic by indicating a colour change are called indicators. Examples: Turmeric, litmus, China rose etc.
Question 5.
What are neutral substances?
Answer:
The substances which are neither acidic nor basic are called neutral substances.
Question 6.
What are natural indicators? Give any two names of the indicators that occur naturally.
Answer:
Indicators which are obtained from natural sources are called natural indicators. Litmus, turmeric, red cabbage, China rose, etc., are some common natural indicators used widely to show the acidic or basic character of substances.
Question 7.
Which acid is present in our stomach ?
Answer:
Hydrochloric acid in small amount is present in our stomach.lt helps us to digest food.
Question 8.
Name the acid present in the following:
a) Tamarind
b) Spinach
c) Lemons and oranges
Answer:
a) The acid present in the tamarind is tartaric acid.
b) The acid present in the spinach is oxalic acid.
c) The acid present in the lemons and oranges is citric acid.
Question 9.
How many types of litmus papers are there? What are they?
Answer:
There are two types of litmus papers. They are red and blue litmus paper.
Question 10.
Which is the most commonly used natural indicator?
Answer:
The most commonly used natural indicator is litmus.
Question 11.
What makes the soil acidic ?
Answer:
Excessive use of chemical fertilisers makes the soil acidic.
Question 12.
What kills fish and other organism present in the water bodies?
Answer:
Releasing of factory waste containing acids or bases.
Question 13.
Define neutralisation.
Answer:
Neutralisation can be defined as the reaction between an acid and a base.
Question 14.
What are salts ?
Answer:
The product formed other than water by the neutralisation reaction of an acid and a base is called salt. Salt may be acidic, basic or neutral in nature. Example: Sodium chloride.
Question 15.
What colour does the phenolpbthalein give when the solution is basic?
Answer:
Phenolphthalein turns pink in bases.
Acids Bases and Salts Extra Questions
Question 1.
Define organic acids.
Answer:
Organic acids are the acids found naturally in plants and animals, For example: Vinegar contains acetic acid, lemon juice contains citric etc., are organic acids.
Question 2.
Look at figure which shows solutions taken in test tubes A, B, C and D. What colour is expected when a piece of red iitinus paper is dropped in each test tube? Nature of the solutions is given in the table for your help.
| Test tube | Nature of solution | Change in colour of red litmus |
| A | Neutral | |
| B | Basic | |
| C | Acidic | |
| D | Neutral |
Answer:
| Test tubesolution in water | Nature of solution | Change in colour of red litmus |
| A (Milk) | Neutral | No change |
| B (Baking powder) | Basic | Colour will change to blue |
| C (Vinegar) | Acidic | No change |
| D (Glucose) | Neutral | No change |
Question 3.
While playing in a park, a child was stung by a wasp. Some elders suggested applying paste of baking soda and others lemon juice as remedy. Which remedy do you think is appropriate and why ?
Answer:
Wasp sting injects a liquid into the skin which is acidic in nature. Hence baking soda is applied as it is basic in nature and neutralises the acid.
Question 4.
How the factory wastes neutralised ?
Answer:
The wastes of many factories contain acids. If they are allowed to flow into the water bodies, these acids will kill fish and other organisms.Therefore the factory wastes are neutralised by adding basic substances.
Question 5.
Why do you mean by soil treatment ?
Answer:
Most of the plants grow best in neutral soil, excessive use of chemical fertilisers makes the soil acidic. Plants do not grow well when the soil is either too acidic or too basic. 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 (compost) is added to it. Organic matter releases acids which neutralises the basic nature of the soil.This process of maintaining soil pH balance is called soil treatment.
Question 6.
What is litmus ? Write its use ?
Answer:
Litmus is the most commonly used indicator which is extracted from lichens.lt is naturally purple in colour but with acids, it turns red and with bases, it turns blue. It is used to detect whether the given substance is an acid or a base.
Question 7.
A small amount of hydrochloric acid is always produced in the stomach. Is it useful or harmful for us ? If excess of acid is produced in the stomach, what should we do?
Answer:
A small amount of hydrochloric acid produced in the stomach is useful as it helps to digest our food and it can kill the harmful bacteria that may enter into the stomach along with the food. If excess of acid is produced in the stomach causes indigestion.We should take an antacid such as milk of magnesia which contains magnesium hydroxide to neutralise the excess acid.
Question 8.
Explain the use of China rose as an indicator.
Answer:
China Rose is a good example of a natural indicator. It has an orange colour in neutral conditions. It changes colour from dark pink to magenta when exposed to acid. It becomes green in basic conditions.
Question 9.
Name any three acids used in the laboratory.
Answer:
Acids which are mostly used in laboratory as below :
- Hydrochloric acid (HCl)
- Sulphuric acid (H2SO4)
- Nitric acid (HNO3)
Question 10.
What are the properties of acids ?
Answer:
The properties of acids are :
- Acids are sour in taste.
- Acids turns blue litmus into red.
- Acids have pH less than 7.
- Acid reacts with meted to form hydrogen gas.
- Acids do not react with ammonium salts.
- Acids are generally found in citrus fruits like lemon, vinegar, curd, amla etc.
Question 11.
What are the properties of bases ?
Answer:
The properties of bases are :
- Bases are bitter in taste and soapy to touch,
- Base turns red litmus to blue.
- It give pink colour with phenolphthalein indicator.
- Bases are generally found in lime water, soap, window cleaner, Milk of Magnesia.
- Bases react with ammonium salts to give ammonium gas.
Question 12.
What does an ant inject when it bites ? How will you treat it ?
Answer:
When an ant bites, it injects the acidic liquid (formic acid) into the skin. The effect of the acid can be neutralised by rubbing moist baking soda (sodium hydrogen carbonate) or calamine solution, which contains zinc carbonate.
Question 13.
How will you prepare lime water ?
Answer:
To prepare limewater, take some water in a tumbler and add some lime (chuna) into it. Stir the solution and keep it for some time. Pour a little from the top. This is lime water.
Question 14.
Explain the use of phenolphthalein as an indicator.
Answer:
Phenolphthalein is a man-made marker. It is colourless in neutral circumstances. When exposed to basic circumstances, it turns pink, and when exposed to acidic ones, it turns colourless.
Extra Questions of Acids Bases and Salts Class 7
Question 1.
What is acid rain ? List some of the damaging effects of acid rain.
Answer:
The rain containing excess of acids called an acid rain. The rain becomes acidic because carbon dioxide, sulphur dioxide and nitrogen dioxide dissolve in rain drops to form carbonic acid, sulphuric acid and nitric acid respectively.
Effects of acid rain are:
- Acid rain makes the water of lakes, ponds and rivers too acidic due to which fish and other aquatic animals get killed.
- Acid rain eats up the leaves of the trees gradually. By losing leaves, the trees die. Acid rain also damages crop plants in the fields.
- Acid rain damages the metal structures like steel bridges, etc., when it falls on them.
- Acid rain damages the surfaces of buildings and monuments made up of marble.
Question 2.
Explain any three neutralisation reactions in our daily life.
Answer:
- Ant bite : When an ant bites, it injects the acidic liquid (formic acid) into the skin. The effect of the acid can be neutralised by rubbing moist baking soda (sodium hydrogen carbonate) or calamine solution, which contains zinc carbonate.
- Indigestion : Our stomach contains hydrochloric acid. It helps us to digest food but too much of acid in the stomach causes indigestion. Sometimes, indigestion is painful. To relieve indigestion, we take an antacid such as milk of magnesia which contains magnesium hydroxide. It neutralises the effect of excessive acid.
- Factory wastes: 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. The factory wastes are, therefore, neutralised by adding basic substances.
Question 3.
Common indicators cannot determine how much acidic or basic solution has. Explain.
Answer:
Common indicators such as litmus, methyl orange and phenolphthale in can easily tell us whether a solution is acidic or alkaline but they cannot easily tell how much a given solution is stronger than another acidic solution. It means they cannot tells us that degree of acidic or basic nature of a solution.
Question 4.
A farmer was unhappy because of his low crop yield. He discussed the problem with an agricultural scientist and realised that the soil of his field was either too acidic or too basic. What remedy would you suggest the farmer to neutralise the soil?
Answer:
The reason for low crop yield in farmer’s field was that the soil at a place is either too acidic or too basic. The soil may be acidic or basic naturally. The excessive use of fertilisers in the fields also makes the soil too acidic. When the soil is too acidic, it is treated with base such as quicklime (calcium oxide) or slaked lime (calcium hydroxide) which neutralises the excess acid present in the soil and reduces its acidic nature. If the soil is too basic, then decaying organic matter (called manure or compost) is added it. The decaying organic matter releases acid which neutralises the excess bases present in the soil and reduces its basic nature.
Case Based / Data – Based Mentions
Sneha and her family went for a trip around river Yamuna, in Delhi is polluting it deliberately. They saw that factory wastes and municipal waste are dumped into it untreated. They thought of spreading an awareness programme. They even wrote to Municipal corporation of the state, suggesting them ways to reduce this kind of pollution.
i) How factory or domestic wastes affect the quality of river?
Answer: Factory or domestic wastes changes colour, acidity or basicity, microbial growth, temperature, turbidity etc., of the water.
ii) How the process of neutralisation is affecting changing some of the quality of water?
Answer: If the river water is it too acidic or basic, club. So by neutralising the pollutants before discharging into the river can at least change water quality to neutral.
iii) Suggest any two ways to reduce the pollution of the river Yamuna?
Answer: Pollution of the river can be reduced largely by making the people aware that how they can contribute in their own level to control water pollution and giving strict guidelines to industries situated near river bank to treat their waste suitably before discharging it into the river.
iv) How the factory wastes are neutralised?
Answer: The factory wastes are neutralised by adding basic substances.