Samacheer Kalvi 8th Science Solutions Chapter 14 Pdf
Tamilnadu Board Samacheer Kalvi 8th Science Solutions Chapter 14: Tamilnadu State Board Solution Class 8 Science Chapter 14 – Acids and Bases.
Samacheer Kalvi 8th Science Solutions Chapter 14: Overview
|
Board |
Samacheer Kalvi |
| Class |
8 |
|
Subject |
Science |
| Chapter |
14 |
|
Chapter Name |
Acids and Bases |
Samacheer Kalvi 8th Science Solutions Chapter 14 Pdf
(I) Choose the best answer.
( 1 ) Acids are sour in taste .
a ) sour
b) sweet
c) bitter
d) salty
(2) Aqueous solution of all of these conduct electricity.
a ) acid
b) base
c) salt
d) All of these
(3) In acidic solutions blue litmus changes into red colour.
a) blue
b) green
c) red
d) white
(4) Base is a substance that gives OH– on dissolving in water.
a) OH-
b) H+
c) OH
d) H
(5) Sodium hydroxide is a base.
a) acid
b) base
c) oxide
d) alkali
(6) Red ant sting contains formic acid
a) acetic acid
b) sulphuric acid
c) oxalic acid
d) formic acid
(7) Magnesium hydroxides are used for treating acidity
a) acidity
b) head pain
c) teeth decay
d) None of these
(8) Acid mixed with base forms salt and water
a) salt and water
b) salt
c) water
d) No reaction
(9) We brush our teeth with toothpaste because it is basic in nature.
a) basic
b) acidic
c) Both a and b
d) None of these
10) In basic solution turmeric indicator paper changes from yellow to red.
a) blue
b) green
c) yellow
d) red
(II) Fill in the blanks .
1 ) Benzoic acids are used for preservation of food.
2) The word sour refers to acidus in Latin .
3) Bases are bitter in taste .
4) Chemical formula of calcium oxide is CaO .
5) Wasp sting contains alkaline substance.
6)Turmeric is used as a indicator.
7) In acidic solution the colour of the hibiscus indicator paper will change to deep pink or deep red.
(III) State true or false, if false correct the statement.
1 ) Most of the acids are not soluble in water.
This statement is false.
Explanation:
It is not correct to say, thatmost of the acids are insoluble in water but rather most of the acids are soluble in water.
2) Acids are bitter in taste .
This statement is false.
Explanation:
Acids are not bitter in taste but instead, acids have a sour taste.
3) Bases are soapy to touch when they are dry.
This statement is false.
Explanation:
Bases are not soapy to touch when they are in dry condition but rather, bases are soapy to touch when they are in aqueous condition.
4) Acids are corrosive in nature.
This statement is true.
5) All bases are alkalis.
This statement is false.
Explanation:
All bases are not alkalis but rather ,all alkalis are base.
6) Hibiscus flower is an example for natural indicator.
This statement is true.
(IV ) Answer briefly .
1 ) Acid – Define .
‘Acidus’ is a latin word from where the term acid is derived and this usually means sour. Acids refers to those chemical compounds which are sour in taste. Therefore ,the release of hydrogen ions from any chemical substances when dissolved in water is known as acids. On the basis of the sources, organic acids and inorganic acids are the two main types of acids. When there is a natural occurrence of acid in fruits and vegetables then it is known as organic acids. Citric acid and tartaric acid are some of the perfect examples of organic acid. On the other hand, the artificial production of acids by the industries are known as inorganic acids. Hydrochloric acid and sulphuric acid are two such examples.
2) Write any four physical properties of acids.
The physical properties of acids are as follows :
- Acids generally have a sour taste.
- Acids does not possess any colour.
- The colour of the indicators are changed by acids. When treated with acids, there is an occurrence of transformation in the litmus paper, which means blue litmus paper transforms into red and in a similar manner, methyl orange transforms into pink.
- There are only a few acids that exists in solid state but most of the acids exist in liquid state only.
3) What are the similarities between acids and bases?
The similarities between acids and bases are as follows:
- Both acids and bases depicts a corrosive nature .
- In aqueous solution, both goes through the process of ionization.
- In aqueous solution, both possess the ability to conduct electricity .
- Both acids and bases participates in the neutralization reaction.
(4) State the difference between acids and bases.
The differences between acids and bases are as follows :
Acids
- H+ ions are produced by acids in water.
- They have a sour taste.
- Most of the acids are in liquid state and only a few of them are in solid state.
- Acid changes the colour of the indicators, as for instance, it transforms blue litmus paper into red.
Bases
- OH- ions are produced by bases in water.
- They have a bitter taste.
- The bases are mostly in solid state.
- Bases also changes the colour of the indicators, as for example, it transforms red litmus paper into blue.
(5) What is an indicator?
An indicator refers to a chemical substance whose primary function is to indicate the acidic or basic nature of a solution by depicting a suitable colour change. Natural indicators and synthetic indicators are mainly the two types of indicators. Natural indicators as the name suggests, refers to those chemical substances that are acquired from the natural resources. Litmus and turmeric juice are one such example. Synthetic indicators on the other hand, refers to an indicator which are made up of artificial substances. Phenolphthalein and methyl orange are some of the relevant examples of synthetic indicators.
6) What is a neutralization reaction?
When an acid and a base react with one another, then it leads to the occurrence of chemical reaction that ultimately helps in the formation of salt and water. This is called neutralization reaction.
7) Write any four physical properties of base .
The physical properties of bases are as follows:
- There are only few bases that exists in liquid state but most of the bases exist in solid state only.
- Bases generally have a bitter taste.
- Bases depicts a corrosive
- Bases does not possess any colour.
(V) Answer in detail .
1) What are the uses of acids?
The uses of acids are as follows :
- The presence of hydrochloric acid in our stomach performs an essential role in digesting our food materials.
- In order to preserve food materials vinegar is used.
- Food materials such as pickles can be preserved by using benzoic acid.
- Due to the presence of higher fatty acids, sodium or potassium salts are mostly used in the preparation of washing and bathing soaps.
- As sulphuric acid acts as a dehydrating agent, for this reason they are used by several industries for the purpose of making detergents, paints, fertilizers and several other chemicals.
- Hydrochloric acid, nitric acid and sulphuric acid acts as an essential laboratory reagents.
- Nucleic acids are contained in the cells of all living organisms. Animals posses deoxy nucleic acid (DNA) , on the other hand plant posses ribo nucleic acid (RNA) .
2) What are the uses of bases ?
The uses of bases are as follows :
1 ) In order to prepare bathing soaps, potassium hydroxide is used.
2 ) Sodium hydroxide is used in the preparation of washing soaps.
3) Sodium hydroxide is used not only in paper industries and textile industries but it is also used for the purpose of making medicines.
4) For white washing , calcium hydroxide is used to a considerable extent.
5) As antacids contains aluminum hydroxide and magnesium hydroxide, for this reason it is used to cure acidity problems.
6) Ammonium hydroxide is used for the purpose of manufacturing fertilizers ,nylon ,plastics and rubber.
(3) Explain the neutralization reactions in our daily life.
It is necessary to balance acids and bases because it is essential for both our health and environment. We experience various neutralization reactions in our day to day life activities. The importance of some of those reactions are as follows :
Bee bite
Formic acid is injected into our body, whenever any bees or red ants bites us. This acid leads to a burning sensation and causes pain. So, in order to neutralize the formic acid , a lime paste is applied which represents a suitable base in the form of calcium hydroxide, so that the pain can be suppressed.
Wasp bite
Whenever a wasp bites us, an alkaline substance is injected in our body by the insect. This alkaline substance gives rise to pain and burning sensation. So ,we use vinegar in order to neutralize the alkalinity because vinegar is an acid.
Tooth decay
The doctors always recommends us to brush our teeth at least twice in a day. If we don’t brush our teeth , then the bacteria that are present on the surface of our tooth will react with the food particles, which in turn will cause acid formation and this acid will lead to tooth decay. So, it is necessary to neutralize the acid in order to avert tooth decay. So, whenever we brush our teeth with tooth paste which contains weak bases, it plays an important role in neutralizing the acid, which will ultimately contribute in keeping our teeth strong and healthy.
Acidity
The presence of hydrochloric acid in our stomach contributes in digesting our food materials. But extensive production of hydrochloric acid in our stomach will lead to the formation of ulcer in our stomach and food pipe. So, antacids which represents a weak base in the form of aluminum and magnesium hydroxide are used for the purpose of neutralizing it. Hence, this helps in removing the acidity.
Agriculture
Acidic soil is unsuitable for the growth of plants. For this reason, fertilizers like powdered lime, limestone or ashes of burnt wood are added to the soil by the farmers ,for the purpose of neutralizing the acidity.
Industries
Industrial effluents contains acids like sulphuric acid. So, before discharging it into the water bodies, it is treated by adding lime in order to neutralize it.
(4) How will you prepare natural indicator from turmeric powder.
A paste can be prepared by adding small quantity of water to turmeric powder. Then this paste will be dried, after applying it on a blotting paper or filter paper. In order to find the nature of the solution, these strips are used as indicators. The turmeric indicator paper does not depict any change in colour in acidic solution. On the other hand, in basic solution turmeric indicator paper depicts a transformation in colour, which means the colour transforms from yellow to red. In this way, we will prepare natural indicator from turmeric powder.
(VI) Higher Order Thinking Questions .
1 ) Vinu and Priyan take their lunch at school. Vinu eats lemon rice and Priyan eats curd rice. Both lemon rice and curd rice are sour in taste . What is the reason?
As we know that, acids generally have a sour taste. So, due to the presence of lactic acid in curd, the curd rice are sour in taste . Simultaneously, citric acid are contained in lemon juice, due to this reason the lemon rice have a sour taste . Owing to this reason, both lemon rice and curd rice are sour in taste.
2) Heshna and Keerthi are friends. Keerthi’s teeth are white without caries, but Heshna has teeth with caries. Why? How it is formed?
When bacteria and damage causing substances like acids , comes into contact with the enamel surface of one’s tooth , then it leads to the formation of caries. Generally, food or drinks contains sugar , and when these sugars from the food content reacts with the bacteria that is present on the surface of one’s tooth then it leads to the formation of acid .