Class 7th || Science || 5. Acid, Base and Salt
Q. What do you meant by a substance? What are its main types?
Ans. A substance is a kind of matter that has definite properties and composition and cannot be separated into The other kind of matter by any physical process.
Every pure substance is made up of the same kind of element.
Substancesces can be divided into three types – 1. Acid, 2. Base and 3. Salt.
1. ACID: The substance that are sour in taste and turn the blue litmus to the reds are called acids. Hydrochloric acid (HCl), Sulphuric acid (H2SO4), Nitric acid (HNO3), Carbonic acid (H2CO3), Acetic acid (CH3COOH) and Phosphoric acid (H3PO4)
Acidic Substances:– There are many substances that contain acid and sour in taste are called acidic substances. For example – lemon, curd, pickles, orange juice, vinegar, etc.
The word acid comes from Latin ‘ACERE’ which means sour.
2. BASE: The substance that are bitter and salty in taste and turn the red litmus to the blue are called base. Sodium Hydroxide (NaOH), Potassium Hydroxide (KOH), Ammonium Hydroxide (NH4OH), Calcium Hydroxide (CaOH) (lime water). etc.
Basic Substances:– There are many substances that contain base and bitter in taste are called Basic substances. For example; soap or soap solution, baking soda, washing soda, etc.
3. Salt:–>
Acid + Base –> Salt + Water
The third substance from in neutralization reaction is called salt. The solution formed in neutralization reaction is neither acidic nor basic in nature such type of solution is known as neutral solution.
Salts are of two types acidic salts and basic salts.
Salt formed by neutralization reaction may be acidic or basic in nature. This Acidic or Basic nature of salt depends upon the strength of acid and base.
Recognization nature of substances:– It is not always possible to know the acidic or basic nature of substances by tasting them. Tasting may be harmful to health.
INDICATOR: The special kind of substances which are used to recognise the acidic or basic nature of the substances are called indicators.
Thus the indicator is a substance that shows the acidic or basic nature of a substance by change in its colour.
Types of Indicator: Indicators can be divided into two types.
1. Natural Indicators and
2. Synthetic or Man-made Indicators
1. Natural Indicator: Indicators that are obtained and used naturally to recognise the nature of the substances is known as Natural Indicators. For example; litmus, turmeric, china rose, red cabbage zirconium etc.
Synthetic Indicator: Indicators that are made in laboratory and used to recognise the nature of the substances is known as Synthetic Indicator. For example; phenolphthalein, methyl orange, thymol blue etc.
NATURAL INDICATORS:
Litmus: A natural dye
Litmus: Litmus is extracted from symbiotic organism called Lichens. Lichens consist of fungi and algae living in symbiotic relationship.
It is the most commonly used naturali indicatoris litmus. It is extractedf from lichens. It has a mauve (purple) colour in distilled water, When added to an acidics solution it turns red and when addedto a basic solution, it turns blue.
Litmus is available in the form of a solution, or in the form of strips of paper, known as litmus paper. Litmus paper also comes in the form of strips of two colours. One is called blue litmus paper and another is called red litmus paper.
Litmus is generally available as red and blue litmus paper.
Turmeric: Turmeric is used as another natural indicator. Turmeric is of yellow colour. Turmeric paper turns into red when it is dipped into basic solution. Turmeric paper does not change its colour with acid.
Turmeric is yellow in natural and acidic solution and red in basic solution.
China Rose: China rose or Gudhal is another natural indicator. China rose solution gives dark pink (magenta) colour with acid and green colour with base.
China rose turns green in basic solution and in water, it is pink and dark pink in acidic solution.
China rose indicator turns acidic solutions to dark pink (magenta) and basic solutions to green.
Q. What is acid rain ? How is it harming the Taj Mahal?
Ans. Acid Rain: Carbon dioxide, sulphur dioxide and nitrogen dioxide released from vehicles and chimneys mix with droplets of rain and turn the rain water acidic. When this acidic water of rain falls over earth, Then this type of rain is known as acid rain.
Acid rain damages the buildings and harm the plants and animals.
Taj Mahal is made up of white marble which is in threat because of acid rain. Many parts of Taj Mahal have got damaged due to acid rain and it's whiteness is also faidding.
Q. Give two difference between acid and base.
Ans. Characteristics of Acids
1. Sour in taste.
2. Turns blue litmus paper red.
Characteristics of Base:
1. Bitter in taste.
2. Turns red litmus paper blue.
Neutralisation:
Q What do you mean by the neutralization reaction explain with example?
Ans. When acid and base reacts both of them neutralize each other and form salt and water. This reaction is known as neutralization or neutralization reaction because acid and base neutralize each other.
Acid + Base –> Salt + Water
Q. What is salt or neutral solution?
Ans.
Acid + Base –> Salt + Water
The third substance from in neutralization reaction is called salt. The solution formed in neutralization reaction is neither acidic nor basic in nature such type of solution is known as neutral solution.
Salts are of two types acidic salts and basic salts.
Salt formed by neutralization reaction may be acidic or basic in nature. This Acidic or Basic nature of salt depends upon the strength of acid and base.
Q. What do you mean by the exothermic reaction? is it exothermic reaction?
Ans.
Exothermic Reactions:– Reactions in which heat is evolved are known as exothermic reactions. In neutralization reaction heat is evolved.
Thus, neutralization reaction is an exothermic reaction. Since, it is an exothermic reaction, so reaction mixture becomes slightly hot.
Q. Explain the neutralization reaction with example.
Ans. Sodium hydroxide is a base and hydrochloric acid is an acid. When solution of sodium hydroxide is mixed with the solution of hydrochloric acid, both neutralize each other and formed common salt (Sodium chloride).
The reaction involved in this can be written as follows:
NaOH + HCl → NaCl + H2O
Sodium chloride (NaCl) is the chemical name of common salt which is used in household it is also known as table salt and Hydrogen oxide (H2O) is the chemical name of water.
Neutralization Reaction in Everyday Life:
There are many uses of neutralization reaction in everyday life.
Indigestion: Our stomach releases hydrochloric acid to kill bacteria; if any; present in food. It also helps in the digestion of food.
Sometime our stomach release more hydrochloric acid in the stomach which starts indigestion. This condition can be painful and causes pain in the stomach.
To neutralize this excess hydrochloric acid a base named Milk of Magnesia [Magnesium Hydroxide (MgOH2)] is used to get rid of such symptoms. It is taken orally.
Milk of magnesia, being a base neutralizes the hydrochloric acid of stomach and gives relief from pain of indigestion.
Such type of chemicals or substances are called antacids.
Ant sting: Ant sting or bee sting contains methanoic acid. Methanoic acid is also known as formic acid which is injected into our skin, while biting by ant or bee, results in pain at the place of bite.
Rubbing baking soda at the batting please gives relief from pain due to ant or bee sting.
Baking soda is a base and neutralizes the effect of injected acid of bee or ant.
Other base, such as zinc carbonate (Calamite solution) is also used in the case of ant or bee sting.
Soil Treatment: Sometimes soil becomes acidic or basic due to excess use of fertilizers or wrong method of harvesting. It affects the yield as plants do not grow properly on such soil.
Acidic soil is treated with base Slaked lime (Calcium hydroxide) or quick lime (Calcium oxide) this neutralizes the acidic nature of soil.
Basic soil is treated with organic matter like using manure. Organic matter releases acid and neutralizes the basic nature of soil.
Factory Waste: Most of the factories wastes are acidic and flushed into rivers. The acid present in it pollutes the water and kills the aquatic organisms.
Thus, the Acidic factory wastes are treated to neutralize with basic substances before being flushed in the river.
NCERT Book Exercise Solution
Q. 1. State differences between acids and bases.
Ans.
1 Acids are sour in taste but Bases are bitter in taste and soapy to touch.
2. Acid turns blue litmus red but Bases turn red litmus blue.
3. An acid and a base neutralise each other and form a salt & water.
A base and an acid neutralise each other and form a salt & water.
Q. 2. Ammonia is found in many household products, such as window cleaners. It turns red litmus blue. What is its nature?
Ans. Since window cleaner turns red litmus paper to blue, so window cleaner is basic in nature.
Q. 3. Name the source from which litmus solution is obtained. What is the use of this solution?
Ans.
Litmus solution is obtained from the symbiotic plant lichens. This Litmus solution is used to detect the acidic and basic property of a substance.
Q. 4. Is the distilled water acidic / basic / neutral? How would you verify it?
And. Distilled water is neutral in character, i.e. it is neither acidic nor basic.
Neutral nature or distilled water can be verified by the use of blue and red litmus paper.
Distilled water is neutral so that it does not change the colour of either blue or red litmus paper.
Q. 5. Describe the process of neutralization with the help of an example.
Ans.
When acid and base reacts both of them neutralize each other and form salt and water. This reaction is known as neutralization or neutralization reaction because acid and base neutralize each other.
Acid + Base –> Salt + Water
NaOH + HCl → NaCl + H2O
Q. 6. Mark ‘T’ if the statement is true and ‘F’ if it is false:
(i) Nitric acid turns red litmus blue. (T/F)
(ii) Sodium hydroxide turns blue litmus red. (T/F)
(iii) Sodium hydroxide and hydrochloric acid neutralize 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)
Ans.
(i) F (ii) F (iii) T (iv) F (v) F
Q. 7. Dorji has a few bottles of soft drink in his restaurant. But, unfortunately, these are not labeled. 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?
Ans.
Dorji will solve this problem with the help of litmus strip.
Dorji would dip blue and red litmus paper in the each of the given bottles.
* Which bottle turns blue litmus paper into red is acidic.
* Which bottle turns red litmus paper into blue is basic.
* Which bottle does not change the colour of either blue or red litmus paper is neutral in nature.
After detecting the acidic, basic and neutral nature of the bottle's of soft drink, Dorji would serve the drink to the customers according to their requirement.
Q. 8. Explain why:
(a) An antacid tablet is taken when you suffer from acidity.
Ans.
Antacid means substance that works against acid. It contains better basic solution.
Antacid tablet is taken in the case of acidity to neutralize the excess acid produced in the stomach and give relief from acidity.
(b) Calamine solution is applied on the skin when an ant bites.
Ans. Calamine solution or zinc carbonate, is a base.
In the case of ant bites, ant injects an formic acid in the skin which causes pain and irritation.
We will apply the calamine solution to neutralizes the effect of inject acid in the course of ant bite. This gives relief from pain.
(c) Factory waste is neutralized before disposing it into the water bodies.
Ans.
Most of the factories wastes are acidic and it flushed into rivers. The acid present in it pollutes the water and kills the aquatic organisms.
Thus, it is necessary to neutralize the factory waste before disposing it into the water bodies.
Q. 9. 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.
Ans.
first of all we will label the test tubes as A, B and C.
Dip the turmeric indicator in test tube A. If the turmeric paper changes to red then the liquid in the test tube is base which is sodium hydroxide. Thus botal A content sodium hydroxide
Keep the both bottles aside.
Now took the bottle of level A of sodium hydroxide in your hand.
Now pour sodium hydroxide in remaining two test tubes label B and C.
Neutralization reaction is exothermic reaction and heat is released in the process so the test tube which becomes warm contains acid and labelled it B.
Other one test tube content sugar solution; which is neutral now level it
C.
Q. 10. Blue litmus paper is dipped in a solution. It remains blue. What is the nature of the solution? Explain.
Ans. If blue litmus paper is dipped in a solution and it would remain blue then the solution may be basic or neutral in character.
Blue litmus paper does not change its colour with basic and neutral solution.
Q. 11. 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
Ans. (iv) only d
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