CBSE 9th Science | Matter- Nature and Behaviour – NCERT Exercise – 3

Matter- Nature and Behaviour – NCERT Exercise – 3

Question 11. Write the steps that you would use for making tea. Use the words solution, solvent, solute dissolve, soluble, insoluble, filtrate and residue.

Answer.

In making tea various steps involved are:

(i) Put some water (solvent) in a pan and put the pan containing water on a lighted gas burner

(ii) After sometime water (solvent) begins to boil, now add appropriate amount of milk and sugar (both milk and sugar are solutes)

(iii) Now stir the contents of the pan with the help of a tea spoon. The sugar (solute) will dissolve and milk will become miscible with water (solvent) A solution is thus formed.

(iv) On further boiling the solution, solute (sugar) gets completely dissolved.

(v) Now add the appropriate amount of tea leaves (solute) to the above solution in the pan. Boil and filter through a sieve. Tea will be collected as filtrate and tea leaves will get collected on sieve as residue.

Question 12. Pragya tested the solubility of three different substances at different temperatures and collected the data as given below (results are given in the following table, as grams of substance dissolved in 100 grams of water to form a saturated solutions)

Substance dissolved Temperature in K
283      293     313     333     353
Solubility
Potassium nitrate 21          32       62     106       167
Sodium chloride 36          36       36        7         37
Potassium chloride 35          35       40       46        54
Ammonium chloride 24          37       41       55        66

(a) What mass of potassium nitrate would be needed to produce a saturated solution of potassium nitrate in 50 grams of water at 313K?

Answer (a).

The amount of potassium nitrate present in 100 grams of water in a saturated solution of potassium nitrate = 62 g. (from table)

clip_image006_thumb1 Amount of potassium nitrate present in

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(b) Pragya makes a saturated solution of potassium chloride in water at 353 K and leaves the solution to cool at room temperature. What would she observe as the solution cools ? Explain.

Answer (b).

If a saturated solution of potassium chloride, which is prepared at 353 K, is allowed to cool to room temperature (298 K), some of it will separate out and will settle down at the bottom of solution (we can see from the table that the solubility of potassium chloride is less at 298 K than at 353-K). Thus, we would observe a white residue at the bottom of the container.

(c) Find the solubility of each salt at 293 K. Which salt has the maximum solubility at this temperature ?

Answer (c).

From the given table we find solubility (the maximum amount of salt that can be dissolved in 100 g of water) of various salts as solubility at 293 K.

solubility of potassium nitrate in 100 g of water = 32 g

solubility of sodium chloride in 100 g of water = 36 g

solubility of potassium chloride in 100 g of water = 35g

solubility of ammonium chloride in 100 g of solubility water = 37 g Thus, we find that at 293 K the solubility of ammonium chloride in water is maximum (37g/100gofwater).

(d) What is the effect of change of temperature on the solubility of a salt?

Answer (d).

with increase of temperature, the solubility of all the given salts increases and it decreases with a decrease in temperature. [This is quite evident from the data given in table].

Question 13. Explain the following, giving examples:

(a) Saturated solution

Answer (a).

Saturated solution: A solution in which no 6. more solute can be dissolved at the same temperature is called a saturated solution Ans. e.g. a solution of sugar in water. At room temperature if any more sugar added to it, it does not dissolved but gets settled at the bottom.

(b) Pure substance

Answer (b).

Pure substance: A pure substance means a single substance (or matter) which can not be separated into other known kinds of matter by any physical process.

The substances, which always have the same colour, taste or texture at a given temperature, are pure substances, e.g. elements and components, ghee, oil, etc.

(c) Colloid

Answer (c).

Colloid: It is a type of solution in which the diameter of particle(solute particles) may range from 1 to 100 nm (nm = nanometer = 10-9m). The particles of a colloidal solution do not settle down under the force of gravity
even on standing for long time. The particles of a colloid are uniformly spread
through out the solution.

Due to smaller size particles the solution appears to be homogeneous but actually a colloidal solution is a heterogeneous mixture e.g. milk.

(d) Suspension.

Answer (d).

Suspension: It is a heterogeneous mixture in which the solid particles are spreads through out the liquid without dissolving in it. These particles get settled as a precipitate if suspension is left undisturbed for some time, e.g. muddy water, milk of magnesia, some paints etc.

[Note: The particle size of suspended particles in a suspension is more than 10-7m.]

Question 14. Classify each of the following as a homogeneous or heterogeneous mixture:

(a) Soda water

Answer. (a) Homogeneous mixture

(b) Wood

Answer (b) Heterogeneous mixture

(c) Air

Answer (c) Homogeneous mixture

(d) Soil

Answer (d) Heterogeneous mixtur

(e) Vinegar

Answer (e) Homogeneous mixture

(f) Filtered tea.

Answer (f) Homogeneous mixture.

 

Question 15. How would you confirm that a colourless liquid given to you is pure water?

Answer.

To confirm whether the colourless liquid given is pure or not? We can proceed as follows:

(i) Filter the given liquid using a very fine filter paper to see if it contains any suspended impurities. If any thing is left on filter paper the given liquid is impure. Otherwise it is pure.

(ii) Evaporate a part of the given liquid in a china dish. If any residue is left it is impure and in case no residue is left it is pure.

(iii) Determine the b. p. of the given liquid. If the b. p. is 100°C (373 K) it is pure water. [Note: B.P. of pure water is 373 K at 1 atmospheric pressure]

Question 16. Which of the following materials fall in the category of pure substances?

(a) Ice

Answer. (a)

Ice: Pure substance (It is pure water in solid state) It is a component.

(b) Milk

Answer (b).

Milk: It is a heterogeneous mixture. Mixtures are impure substance. Milk is a colloid.

(c) Iron

Answer (c).

Iron: Pure substance (It is an elements)

(d) Hydrochloric acid

Answer (d).

Hydrochloric acid: It is an impure substance. It is a homogeneous mixture. It is a solution of gas in a liquid.

(e) Calcium Oxide

Answer (e).

Calcium oxide: It is a pure substance (It is a compound)

(f) Mercury

Answer (f).

Mercury: It is a pure substance (It is an elements)

(g) Brick

Answer (g).

Brick: Heterogeneous mixture so impure substance.

(h) Wood

Answer (h).

Wood: Heterogeneous mixture so impure substance.

(i) Air.

Answer (i).

Air: It is homogeneous mixture so impure substance.

Question 17. Identify the solution among the following mixture:

(a) Soil

Answer (a).

Soil is not a solution. It is not a homogeneous mixture.

(b) Sea water

Answer (b).

Sea water is a solution. It is a homogeneous mixture.

(c) Air

Answer (c).

Air is a solution. It is a homogeneous mixture.

(d) Coal

Answer (d).

Coal is not a homogeneous mixture so it is not a solution.

(e) Soda water

Answer (e).

Soda water is a homogeneous mixture so it is a solution.

[A solution is a homogeneous mixture]

Question 18. Which of the following will show “Tyndall effect”

 

(a) Salt solution
(b) Milk
(c) Copper sulphate solution
(d) Starch sol.

Answer. “Tyndall effect” is shown by colloidal solution. So, it will be shown by milk, starch sol and not by salt solution, copper sulphate solution is a true solutions and not colloidal solution.

Question 19. Classify the following into elements compounds and mixtures:

(a) Sodium
(b) Soil
(c) Sugar solution
(d) Silver
(e) Calcium carbonate
(f) Zinc
(g) Silicon
(h) Coal
(i) Air
(j) Soap
(k) Methane
(l) Carbon dioxide
(m) Blood.

Answer.

(a) element

(b) mixture (heterogeneous mixture)

(c) mixture (homogeneous mixture)

(d) element

(e) compound (CaCO3)

(f) element

(g) element

(h) mixture (heterogeneous mixture)

(i) mixture (homogeneous mixture)

(j) mixture

(k) Compound (CH4)

(l) Compound (CO2)

(m) mixture

Question 20. Which of the following are chemical changes ?

(a) growth of a plant

Answer (a).

It is a chemical change.

(b) rusting of iron

Answer (b)

It is a chemical change

(c) mixing of iron filings and sand

Answer (c)

It is a physical change

(d) cooking of food

Answer (d)

It is a chemical change

(e) digestion of food

Answer (e)

It is a chemical change

(f) freezing of water

Answer (f)

It is a physical change

(g) burning of a candle.

Answer (g)

It is a chemical change.

 

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Science IX | Natural Resources: Our Environment | Part 3

Natural Resources: Our Environment | Part 3

Soil

Soil is the portion of the earth’s surface consisting of disintegrated rock and decaying organic material. It provides the support for many plants and animals. Thickness of soil on the earth’s surface ranges from a few millimeters to 3-4 meters. Terrestrial plants depend for their nutrients, water supply and anchorage upon the soil. Even for the aquatic plants, the soil is important as chief storage of all the nutrients which are made available to the water medium.

1. Formation of soil :

Soil is formed from the rocks by undergoing the following two processes :

1. Weathering ;

2. Paedogenesis

A. Weathering.

Breakdown of bigger rocks into fine smaller mineral particles is called weathering. Weathering occurs by following three means :

(i) Physical weathering :

This is done by various climatic factors such as temperature, wind, rain water, ice, snow, glaciers and running water. Water and high temperature cause corrosive humidity and bring about unequal expansion and contraction or rocks, facilitating their breakdown. Rock pulverizing glaciers, low temperature and water grind the rocks. The freezing water expands in rock crevices and breaks the rocks. Wind action also causes the weathering of rocks. River water grind rock chips and stones into sand and into more fine form – the slit. Soluble components of rocks such as calcium, chloride, sulphates, etc., are removed by water in solution ; they percolate downward. The roots of the plants also have a role in weathering process. They penetrate into the crevices of the rocks and enhance rock-breaking process.

(ii) Chemical weathering :

It involves a variety of chemical processes such as hydrolysis, hydration, oxidation and reduction. Chemical weathering, for example, involves the breaking down of complex compounds by the carbonic acid present in water and by acidic substances derived from the decomposition process of organic matter in soil. The main end products of the chemical weathering are silica, clay, inorganic salts and hydrated oxides.

(iii) Biological weathering :

Lichnes, bryophytes (mosses) and other plants live on rocks and produce acids, which accelerate the process of rock weathering.

B. Paedogenesis (soil development) :

This process involves the decomposition process by bacteria and fungi by which organic material s are broken down and leads to humification and mineralization. Detritivores such as nematodes, earthworms and artropods such as scolopendra, millipede, mites and ants consume organic matter and add excretory nitrogen to it. Thus, addition of organic matter (humus) from dead and decomposed plants and animals is the final stage in the formation of soil. A mature soil has minerals, stored energy in the form of organic matter (such as starch, sugars, cellulose, lipids, proteins, oxides of nitrogen (NO2, NO3, NH+ ions), water and air.

Soil Erosion

The removal and transportation of top layer of soil from the original position to another place with the help of certain agents such as strong winds and fast running rainwater is called soil erosion. The top layer of soil is fertile. It provides anchorage (firm support) to plants and is also source of nutrients and water to the plants.

Soil erosion normally occurs n bare areas, i.e., areas without plant cover. It is so because the bare topsoil is loose and thus can easily carried away by strong winds or fast moving water of heavy rains or rivers.

Biogeochemical Cycles

A constant interaction between the biotic and abiotic components of the biosphere makes it a dynamic, but stable system. These interactions consist of a transfer of matter and energy between the different components of the biosphere. Let us look at some processes involved in the maintenance of the above balance.

The Water or Hydrological cycle

Water evaporates from the hydrosphere (oceans, seas, rivers, streams, lakes, ponds, moist soil) with sun’s heat and forms clouds. By the help of wind, the clouds are blown over the land, where they are cooled enough to drop the water as rain, hail and sleet (called precipitation). Rain may fall directly into the oceans also.

The organisms get water from and return it to the global water cycle. Plants absorb water from the soil or water reservoir and ad it to the air as vapour by transpiration. Water transpired by trees cools the surrounding air, and plays a role in determining the microclimate around them. Animals take water from the water reservoir or with food (plants, or other animals or their products). They return it to the air as vapours by respiration or to the soil as fluid by excretion. Mammal excrete water also as sweat which evaporates from their bodies. Water is also added to the environment by death and decay of organisms. Water vapor formed by transpiration and respiration form clouds and enter global water cycle.

The Nitrogen Cycle

In our atmosphere nitrogen gas makes up 78% nitrogen one of the essential part of living molecule like protein, nucleic Acid (DNA & RNA) and vitamins. It also found in alkalides and urea which are important biologically compounds.

Nitrogen is thus in essential nutrient for all life form and life would be simple if all these life forms could use the atmospheric nitrogen directly. However, other than a few form of bacteria, life form are not able to convert the comparatively inert nitrogen molecule into form like nitrates and ‘nitrites fixing’ bacteria are found in roots of legumes plants (Generally the plants which give us pulses). The other manner in which the nitrogen molecules are converted into nitrates and nitrites by physical process. During lighting the high temperature and pressure created in the air convert nitrogen into oxides of nitrogen. These oxides dissolves in water to form nitric and nitrous acid and fall an land along with rain. These re them utilized by various life forms.

Plants generally take up nitrates and nitrites and convert them into Amino Acid which are used to make proteins and other complex biological compound are subsequently consumed bacteria Animals. Once the animals or the plant dies, other bacteria in the soil convert the various compound of nitrogen back into nitrates and nitrites. A different type of bacteria converts the nitrates and nitrites into elemental nitrogen. In this way nitrogen cycle occur in our atmosphere.

The Carbon Cycle

Carbon is found in various forms on the Earth. It occurs in the elemental form as diamonds and graphite. In the combined state, it is found as carbon dioxide in the atmosphere, as carbonate and hydrogen carbonate salts in various minerals, while all life forms are based on carbon containing molecules like proteins, carbohydrates, fats, nucleic acids and vitamins. The endoskeletons and exoskeletons of various animals are also formed from carbonate salts. Carbon is incorporated into life forms through the basic process of photosynthesis which is performed in the presence of sunlight by all life forms that contain chlorophyll. This process converts carbon dioxide from the atmosphere or dissolved in water into glucose molecules. These glucose molecules are either converted into other substances or used to provide energy for the synthesis of other biologically important molecules.

The utilization of glucose to provide energy to living things involves the process of respiration in which oxygen may or may not be used to convert glucose back into carbon dioxide. This carbon dioxide then goes back into the atmosphere. Another process that adds to the carbon dioxide in the atmosphere is the process of combustion where fuels are burnt to provided energy for various needs like heating, cooking, transportation and industrial processes. In fact, the percentage of carbon dioxide in the atmosphere is said to have doubled since the industrial revolution when human beings started burning fossils fuels on a very large scale. Carbon, like water, is thus cycled repeatedly through different forms by the various physical and biological activities.

The Oxygen Cycle

Oxygen is a very abundant element on our Earth. It is found in the element form in the atmosphere to the extent of 21%. It also occurs extensively in the combined form in the Earth’s crust as well as also in the air in the form of carbon dioxide. In the crust, it is found as the oxides of most metals and silicon, and also as carbonate, sulphate, nitrate and other minerals. It is also an essential component of most biological molecules like carbohydrates, proteins, nucleic acids and fats (or lipids).

But when we talk of the oxygen-cycle, we are mainly referring to the cycle that maintains the levels of oxygen in the atmosphere. Oxygen from the atmosphere is used up in three processes, namely combustion, respiration and in the formation of oxides of nitrogen. Oxygen is returned to the atmosphere in only one major process, that is, photosynthesis. And this forms the broad outline of the oxygen-cycle in nature.

Though we usually thing of oxygen as being necessary to life n the process of respiration, it might be interest to you learn that some forms of life, especially bacteria, are poisoned by elemental oxygen. In fact, even the process of nitrogen-fixing by bacteria does not take place in the presence of oxygen.

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