ACIDS AND BASES
ACIDS: They are sour in taste. Substances which contain acids are lemon juice, curd etc.
They are called acidic.
Word Acid comes from Latin word ‘acere’ means sour.
ACID | FOUND IN |
Acetic acid | Vinegar |
Formic acid | Ant’s sting |
Citric acid | Citrus fruits |
Lactic acid | Curd |
Oxalic acid | Spinach |
Tartaric acid | Tamarind |
Ascorbic acid | Amla , citrus fruits |
BASES: They are bitter in taste and feel soapy on touch. For example, baking soda. These types of substances are called basic.
BASE | FOUND IN |
Calcium hydroxide | Lime water |
Ammonium hydroxide | Window cleaner |
Sodium hydroxide | Soap |
Magnesium hydroxide | Milk of magnesia |
INDICATORS
Indicators are the substances which are used to identify acidic or basic substance by changing color when added to a solution. For example, turmeric, litmus, china rose (natural indicators), phenolphthalein etc.
LITMUS ( natural dye)
Most commonly used.
Produced from lichens. (lichens are symbiosis of fungi and algae)
In distilled water, it is purple (mauve) in color.
Used in form of solution or paper strips called as litmus paper.
Acidic substance- changes blue litmus paper to red.
Basic substance- changes red litmus to blue.
Substances which do not change the color of both red and blue litmus paper are called neutral substance. They are neither acidic nor basic.
CHINA ROSE (GUDHAL FLOWER)
Solution is obtained by putting china rose petals in warm water till the water becomes colored. This solution is used as indicator.
It turns acidic solution to Dark pink color (magenta color).
It turns basic solution to green color.
PHENOLPHTHALEIN
If basic solution is there, phenolphthalein gives pink color.
If acidic solution is there, phenolphthalein remains colorless
ACID RAIN:
Rain having excess acids in the rainwater is called acid rain.
Oxides of sulphur and nitrogen, which are air pollutants, dissolve in the rain drops and convert to sulphuric acid & nitric acid . It makes rainwater acidic.
Acid rain is harmful to plants and animals and causes damage to buildings, monuments etc.
NEUTRALISATION
When an acid and a base react with each other, they neutralize the effect of each other. This is called neutralisation.
ACID + BASE ———> SALT + WATER + HEAT
Example,
Sulphuric acid (H2SO4) + Sodium hydroxide (NaOH) —> Sodium sulphate (Na2SO4) + H2O + heat
(Acid) (Base) (Salt)
Product formed by neutralisation reaction is salt. Salt is neither acidic nor basic, it is neutral.
NEUTRALISATION IN EVERYDAY LIFE
INDIGESTION: Hydrochloric acid in stomach helps to digest food. But if this acid gets high, it causes indigestion which can cause pain. To relieve from this, antacid (milk of magnesia) is taken which neutralizes the acid.
ANT BITE: Ant sting contains formic acid. When ant bites, it releases the acid in the skin which causes burning and itching. To relieve this, baking soda (sodium hydrogen carbonate) or calamine solution (zinc carbonate) is applied.
SOIL TREATMENT: If soil is too acidic or basic, plants do not grow well. Excessive use of chemical fertilizers can make soil acidic.
If soil is too acidic, then bases can be added such as quick lime (calcium oxide), etc.
If soil is too basic, then organic matter (compost) can be added which releases acids in the soil.
FACTORY WASTES: Waste which is produced from factories is acidic in nature. Waste is released into the rivers which causes harm to water organisms. Waste can be neutralized by adding basic substances.
Fibers can be obtained from the natural or artificial sources.
Natural resources – The resources which are provided by nature through plants and living organisms.
Artificial resources – The resources which are developed by humans.
So, here we will study about the fibers which are obtained from animals. like wool, silk etc.
WOOL-
The wool we use come from sheep, goat, yak, etc. animals. These animals have hair (or FLEECE) on their body which is like a thick coat over them. This thick coat of hair traps heat and keep animals warm. We derive wool from their hairs.
This skin having hairs over it has two types of fibers –
Coarse beard hair
Fine soft under hair
The second type, that is, fine soft under hair are the one from which wool is derived.
But some sheep’s breed does not have coarse beard hair and have only fine soft under hair. The process of selecting parents so that their offspring (animal’s baby) could have the special characteristics like having soft under hair, is called as ‘Selective Breeding’.
Animals yielding wool –
Sheep
Yak (common in Tibet and Ladakh)
Angora goats (Mohair in Jammu and Kashmir)
Camel fur
PROCESSING FIBRE INTO WOOL –
SHEARING – This is a process name in which fleece or hair of sheep along with a thin layer of skin is removed from body of sheep. This process is done in summer because this coat of skin provides warmth to sheep which is not good in hot weather.
SCOURING – After shearing, the hair obtained contains dirt, grease, and dust. To remove this, they are washed properly in tanks and this process is called as scouring.
SORTING – This process is done in factory. It means to separate or sort different hair as they have different textures.
There are some small fluffy fibers known as burrs. These are picked out from hair and then the remaining hair are again scoured or washed. Then the wool become ready to draw into wool fibers.
DYE- This means to provide colour to fibers as natural colour of wool fiber obtained from fleece is black, white or brown.
Then the fiber is straightened, combed and rolled into yarn. If it is a longer fiber then it is for sweaters of wool and if it a smaller fiber then it is spun and woven into woollen cloth.
CHEMICAL CHANGES
It is a type of change in which chemical composition of a substance changes. It takes place because of chemical reaction. There is formation of new substance. For example – rusting, corrosion, baking a cake, burning of paper, etc.
Let’s take example of a Magnesium ribbon. After cleaning it with a sandpaper we bring this near a flame.
We will see that it burns with a dazzling white flame. And after burning, we will get a white powder of MgO (magnesium oxide). It will be a chemical change because a new substance is formed and there is a chemical reaction also involved.
2Mg + O2 —–> 2MgO
(Magnesium + Oxygen ——-> Magnesium Oxide)
Now this magnesium oxide gets mixed with water.
The reaction involved will be –
MgO + H2O —–> Mg (OH)2
(This reaction also provides a new substance Magnesium Water Magnesium Hydroxide through CHEMICAL CHANGE)
Oxide
Magnesium Oxide is basic in nature. (It will convert red litmus to blue)
Other examples are like:
Vinegar + Baking soda ———> CO2 + other compounds
(acetic acid) (sodium hydrogen
carbonate)
**Carbon dioxide – CO2
Lime water – Ca (OH)2 (also called Calcium Hydroxide)
Calcium carbonate – CaCO3
CO2 + Ca (OH)2 —> CaCO3 + H2O
**This CaCO3 formed makes water milky.
There are some other changes also associated with chemical reactions and chemical changes –
There can be sound production also
There can be absorption or production of heat or light or even rays
There can be change in smell of substance as new substance can have different properties
Colour change is also possible
Production of new gases along with other products
For example, when we burn a firecracker. Lot of heat, light and sound is produced.
Colour of apple is changed when it is left after cutting it.
In all these, a new substance is formed means a chemical reaction takes place which leads to chemical change.
A material or substance has two kind of properties –
Physical Properties – These are the properties which can be observed in a substance. They can be checked or observed without making any change in their chemical composition. For example – colour, odor, texture, melting point, boiling point, etc.
Chemical properties – These are the properties which are observed when the substance undergoes a chemical reaction. The atoms from which that substance is made up get changes during a chemical reaction.
When a thing gets converted into another thing or there is slight addition – subtraction of things in it, it is said to be changed. There are two types of changes :
Physical changes
Chemical changes
PHYSICAL CHANGES – It is a type of change in which the physical properties of substance changes, but its chemical properties remain the same. In this kind of change, NO NEW substance is formed.
For example – breaking a glass, crushing a paper, mixing salt and water, change of state, etc.
Let us take an example – If we boil some amount of water in a beaker, then it gets converted from liquid to gas form. It means there is change in state, but no new substance is formed. This is a physical change.
RUSTING
It is a reddish-brown substance which is formed over iron articles. It is formed by reaction of iron, oxygen, and water. The reaction is –
Fe + O2 + H2O ——> Fe2O3
(iron) (oxygen) (water) ——-> (RUST)
** For rusting to happen , it is important that both oxygen- water are present.
** If there is more humidity, process of rusting will be faster as there will more amount of air as well as
water.
Due to rusting there is a huge loss. As iron is present everywhere and highly used in industries like ships, cars, bridges, etc.
HOW TO PREVENT RUSTING?
Coating paint or grease regularly
Galvanization – This means to deposit a layer of iron or zinc over the iron article to protect it from rusting.
**Iron which is used in Ships has to be replaced every year. This is because ship has to go in sea which contains a lot of salts dissolved in it. This makes the rusting process faster and more efficient.
**Stainless steel – Type of steel which is made by mixing iron, carbon, nickel, manganese and chromium.
This type of steel does not get rusted.
CRYSTALLIZATION
Process in which large crystals of pure substances are formed from their respective
solutions.
For example, For making crystals of CuSO4 (Copper sulphate) –
Take a beaker and a cup of water in it.
Add some drops of dilute Sulphuric acid in it.
Start heating it.
When it starts boiling then add powder of copper sulphate slowly.
Keep stirring continuously
Keep adding the powder unless capacity of water is reached to add powder in it.
Now filter this solution.
Let it be cool and don’t disturb it.
After sometime we will observe crystals of CuSO4.
SOIL
Soil is a natural resource which contains inorganic (minerals, etc.) and organic material (carbon, nitrogen, etc.) . It forms the surface of the earth.
ROLES OF SOIL:
It is essential for growth of plants.
Many organisms live in the soil such as insects, worms, etc.
It is essential for agriculture.
Soil absorbs water and makes it available to plants.
Soil is polluted by polythene bags and plastics. It also results in death of organisms living in soil.
HUMUS
The organic matter formed in the soil formed by the dead and decaying plants and animals is called humus.
WEATHERING
Weathering is a natural process of formation of soil through breakdown of rocks by action of water, wind and climate.
Nature of soil and the vegetation that will grow in it depends on the rock from which it is formed.
SOIL PROFILE
Soil profile is the vertical section of different layers of soil. Layer is called as horizon. Each layer has different texture, color, composition, depth.
Different layers of the soil are:
A-HORIZON OR TOPSOIL:
Uppermost layer.
Dark in color, soft, porous.
Retain more water.
Fertile layer because it is rich in humus that provides nutrients to plants.
Many organisms live in this layer.
Roots of small plants are fully embedded in this layer.
B-HORIZON OR SUBSOIL:
Middle layer.
Contains more minerals and lesser humus.
Harder and more compact.
Contains sand, silt and clay.
C-HORIZON OR SUBSTRATUM:
Third layer.
Consists of weathered rocks.
Made up of small lumps of rocks with cracks and crevices.
BEDROCK:
It is present below the C-Horizon. It is hard and difficult to dig up.
TYPES OF SOIL
On the basis of quantity of particles of different sizes present, soil is of following types:
SANDY SOIL
Sand particles are present which are big in size.
Large air spaces present between particles (well aerated) and light in weight.
Water drains quickly so this soil is dry.
CLAYEY SOIL
Particle size is smaller than the sandy soil.
Particles are tightly packed, so little space is present between them.
Soil is heavy and holds more water.
Rich in minerals.
LOAMY SOIL
Consists of sand, clay and silt (deposits in rivers).
Silt has size between sand and clay particles size.
Humus is present.
Good water holding capacity.
Best soil for growing plants.
PROPERTIES OF SOIL
PERCOLATION
Absorption of water by soil is called percolation.
PERCOLATION RATE: It is the amount of water absorbed by soil in unit time.
Percolation rate (mL/min)= amount of water (mL)
Percolation time (min)
For example, if soil takes 10 min to absorb 100mL of water, then
Percolation rate= 100 mL = 10 mL/min
10 min
Sandy soil has highest percolation rate and clayey soil has lowest.
MOISTURE IN SOIL
Soil can hold water which can make it moist. This is the moisture of the soil. It depends on the water holding capacity of soil.
Clayey soil has highest water holding capacity.
RETENTION
It is the water holding capacity of soil.
WATER ABSORPTION
Percentage of water absorbed by soil is calculated as:
% of water absorbed= Volume or weight of water absorbed by soil (mL) x 100 [1mL water= 1g]
Weight of the soil (g)
SOIL AND CROPS
Soil profile and composition are affected by factors such as temperature, light, rain, etc.
Paddy is grown in clayey soil as they are rich in organic matter and has good water holding capacity.
Lentils and other pulses are best grown in loamy soil.
Cotton is grown in both loamy and sandy soil.
Wheat is grown in both loamy and clayey soil as they are rich in humus and minerals.
SOIL EROSION
Soil erosion is the removal of top layer of the soil by the action water, wind, etc.
It occurs due to loosening of the soil because of absence of plants. It more occurs in the desert areas where plants are not much.
Water cycle
Water cycle is continuous but due to a lot of reasons the water table is going down and world is facing water shortage.
Water depletion – This occurs when more amount of water is withdrawn than the amount added through seepage of rainwater.
Reasons are –
Increasing population – As population is increasing, demand of water is also increasing. Water is used for construction work, household chores, in offices, road construction etc. Also, due to usage of marbles and cements, less amount of water is allowed to seep in the ground.
Increasing industries – Every industry uses water in one or other way. Number of industries are increasing continuously. Water used by many of the industries is taken from ground.
Agricultural activities – Most of the farmers rely on rain for irrigation purposes. But there can be erratic rainfall.
Due to this reason, farmers have to switch to groundwater for irrigation. This leads to decrease in water table.
Deforestation – Plants transfer moisture from soil to air. Which means they are also responsible for rain. Deforestation (cutting of trees) leads to decrement in number of plants and trees which ultimately leads to less rainfall. This affects the water table by decreasing it.
DISTRIBUTUION OF WATER – Water is distributed in an uneven manner in world. At some places, there is good amount of water. They are water – rich places. But some places are having acute water scarcity.
For example, in India itself some places have excessive rainfall resulting in floods. But in other parts of India, rainfall is absent resulting in droughts many times.
WATER MANAGEMENT –
Many a times water is wasted in high quantity. For example – leaking of supply pipes, water wasting during brushing, bathing, washing, etc.
We can conserve water through RAINWATER HARVESTING. It is the process of collecting or saving the rainwater and use it. It Is also called as WATER HARVESTING.
There are two ways for harvesting water –
We can collect rainwater on the rooftop of our house and then collect this water in a storage tank. After purifying it we can use this water.
Make the rainwater flow underground by making drains or pits. So that when rain comes, this water can directly be sent underground and add to water level.
DRIP IRRIGATION– This is a technique of watering the plants by making use of narrow tubes which can deliver the water directly to the soil or base of the plant.
** If plants do not get water, they will be no be able to get all nutrients from soil and then they cannot prepare food. This will bring whole world to an end as without plants there will be no oxygen and no food.
As a responsible citizen we should ,
Shut Off tap tightly so that no water is leaked
Repair leaking taps
Do not play with water
Use it wisely
Try less quantity of water is used
Making people aware about this issue
We celebrate ‘WORLD WATER DAY’ on 22 March.
According to United Nations, a minimum of 50 liters of water per person per day is recommended.
There are many areas in the whole world where there are acute water shortage and people are not getting adequate amount of water for use.
