Cls 10 Sci act sln chp 3

 Class 10 Science 

 Chapter 3 Metals And Non Metals 

 Activity Solutions 

Activity 3.1

Brief procedure:

Activity 3.1 asks us to check the appearance of some metals and see changes it after rubbing it with sandpaper.

Observation: 

We see these metals look dull.

After rubbing with sandpaper all these materials shine.

Explanation: 

Metals like iron, copper, magnesium, sodium are reactive metals. These metals react with oxygen and form their oxide on the outer layer. Metal oxides are dull in colour. As a result, the metal loses its lustrous property.

e.g. Iron forms a brown layer which we call rusting of iron; aluminium forms smoke colour aluminium oxide; copper forms a black and green layer with oxygen and sulphur etc.

When we rub the metals with sandpaper, its outer oxide layer is scraped out.

You may recall the burning of magnesium in chapter one. here we first clean the magnesium ribbon. It was because magnesium oxide interferes in burning. See: Why should a magnesium ribbon be cleaned before burning?

Interesting fact:

Silver, gold, platinum are very less reactive metals. They do not react with atmospheric air or water. As a result, their shine persists longer, and people use them as jewelry items.

Activity 3.2

Brief procedure:

Activity 3.2 asks us to cut various metals and note the observation.

Observation:

Metals are hard and can not be cut easily. Only magnesium is easily cut. Aluminium require more effort while iron is very hard to be cut by a knife.

Explanation:

Atoms of a metal are stongly connected to its neighbor atoms by a strong attractional force. This makes them hard and difficult to be cut.

Inference/conclusion:

This experiment demonstrates metals have strong inter moleculare force of attraction and are difficult to cut.

Extras

In case of aluminium the there is a shiny layer below the outer layer.

This happens because the outer layer of metals reacts with the atmospheric oxygen to form metal oxides. Metal oxides do not have lustrous property. When we cut the metals using a knife its inner unoxidised layer come into view which shines.

Application:

Metal oxides are a bad conductor of electricity. The oxidation of metals in an electric component may lead to failure. So, we coat metals in circuit with unreactive metals like gold in costly computer parts. It saves them from oxidation.

Activity 3.3

Brief procedure:

Activity 3.3 asks us to strike a metal with a hammer and observe what happens.

A blacksmith strikes an iron piece with a hammer to get the desired shape.

Observation: 

Metal become thin, and it’s surface area increases.

Explanation:

When we hit metal with a hammer or other hard objects metal spreads into a thin sheet. We call this property of metal Malleability.

Inference/conclusion:

This experiment shows that metals are malleable.

Application:

Blacksmith: A blacksmith ( Lohar) heats an iron rod in the furnace and then beats with a hammer until he gets the desired shape.

Steel sheet on the roof is also an application of this property.

Activity 3.4 

Brief procedure:

Activity 3.4 asks us to list some metals which find its use in the wire.

Answer: 

Aluminium, copper, nickel, chromium, gold, silver.

Application:

A typical electric pole uses aluminium as wire, as it is cheaper than copper.

In normal homes, we use aluminium (white core) or copper wire (Golden colour). Now Aluminium wires are less common as copper wires are a better conductor of electricity.

An electric wire on pole still uses aluminium wire because the copper wire is very costly.

Nickel and chromium have lesser conductivity. They are mixed to form nichrome wire. Some wired electric heater consists of nichrome wire.

Apart from all these metals, precious metals like silver and gold also find use in the electronic industry as wire.

They have very high thermal and electrical conductivity. As a result, we use them as a coating in high-quality switches and plugs.

Some electric circuits also consist of silver or gold wires.

Activity 3.5

Brief procedure:

The activity asks us to heat a metal wire which is attached to a pin at its corner by a wax.

Observation: 

The pin drops immidiately once we start heating the wiwires.

Explanation:

Metals are a good conductor of heat. Here, once we start heating, heat transfers to the area of wax. It melts the wax. So, the pin drop on the table. 

Inference/conclusion:

This experiment demonstrates that metals are a good conductor of heat

Application:

Processor cooler in computers and laptops: In a computer and a laptop CPU is the most important chip. During data processing, it generates a lot of heat. To dissipate the heat, a CPU is connected to a copper or aluminium heat sink. Due to the thermal conductivity of metals heat transfers to the heat sink. A fan at the sink blows the hot air outside.

Cooking utensils: Cooking utensils consists of a metal or metal alloys. It receives heat from the gas stove and transfers heat to the food.

Facts:

Metals have free electrons in their valance shell. When we heat a metal, their electrons vibrate and transfer heat to another electron. As a result, metals are a good conductor of heat.

Activity 3.6

Brief procedure:

Activity 3.6 asks us to connect a metal wire with a bulb in series and see what happens to the bulb.

Observation: 

The bulb glows as bright as earlier.

Explanation:

Metals have free electrons in their valance shells. These free electrons move from one position to another. As a result, metals are a good conductor of electricity. When we connect a build to the battery by metal wires, electricity passes from the battery to the bulb. As a result, the bulb starts glowing.

Inference/conclusion: 

This experiment demonstrates that metal wires are a good conductor of electricity.

Application: 

In making wires at home, in making electric circuit board etc.

Some Facts:

When someone is electrocuted, we do not use a metal stick but we use a wooden or plastic stick. Metal stick or rods are good conductors of electricity. If someone tries to save an electrocuted person by that stick, he himself will get electrocuted.

Activity 3.7 

Brief procedure:

Activity 3.7 asks us to compare the properties of metals discussed in earlier activities with some common non-metals.

Answer: 

In activities from 3.1 to 3.6, we studied various properties of metals. They are:

1. Lusture 2. Hardness 3.Malleability 4. Ductility 5. Electric conductivity 6. Heat conductivity.

Metals generally carry all these properties except a few like mercury which is soft (liquid), Sodium and lithium which are not hard. Most non-metals have contrasting features with few exceptions like coal and graphite and diamond which are hard. Below table summarises the properties of some common non-metals.

Activity 3.8 

Brief procedure:

Activity 3.8 asks us to react oxides of metal and non-metals with water and check if it is acidic or basic in nature.

Observation:

We get metal oxide by burning the metal in the presence of oxygen. Metal oxide reacts with water to give a base. It turns the red litmus paper blue.

Similarly, the burning of non-metal produces its oxide. The solution of oxides of non-metal with water turns the blue litmus paper into the red.

Explanation: 

Burning Magnesium ribbon

Magnesium

Magnesium burns in air to form its oxide. See activity 1.1.

2Mg(s) + O2(g) ———–> 2MgO(s)

Magnesium oxide reacts with water and forms Magnesium Hydroxide.

MgO(S) + H2O(l) ———–> Mg(OH)2 (aq)

Magnesium hydroxide is a strong base. It makes the solution alkaline. So, the PH paper turns blue.

Application:

Many antacid syrups contain metal oxides like magnesium oxide and aluminium oxides. These metal oxides form respective metal hydroxide in the stomach and neutralises the acidity.

Sulphur:

Sulphur is a reactive non-metal; it burns to produce its oxide.

S(s) +O2(g) ————-> SO2(g)

Sulphur dioxide dissolves in water and forms sulphurous acid.

SO2(g) + H2O(l) ———–> H2SO3 (aq)

Sulphurous acid is a weak acid. Its 0.1N solution gives the PH of 1.5 which turns the blue litmus red.

Activity 3.9

Brief procedure:

Activity 3.9 asks us to burn various metals and observe their flame.

Burning of copper

Observation: 

Not all metals burn easily, Copper and aluminium take time to burn.

Flame colour:

Sodium: Yellow

Magnesium: White

Aluminium: Silver white

Copper :blue flame

Solubility:

Highly reactive metals like sodium and potassium reacts with water and form soluble hydroxide. But most other metals are not so reactive. So they are not soluble in water.

Only some metal oxides that from metal hydroxide with water, are soluble in water. Else they are insoluble. Beryllium and magnesium are exceptions as they are slightly soluble in water.

Metal oxide + H2O(l) ———> Metal Hydroxide.

Explanation:

Metals are highly reactive elements. They react with oxygen readily to form metal oxides. Highly reactive metals like lithium, sodium, potassium, beryllium, magnesium react spontaneously. Other metals like Aluminum, copper take time to burn. It produces a specific flame colour. Many times flame colour is used to find the constituent of the substance.

Metal + O2(g) ———> Metal oxide(s)

Inference/conclusion: 

Metals on the heating burn to produce its oxides. During this process, they produce characteristic flames.

Activity 3.10

Brief procedure:

Activity 3.10 asks us to react to various metals with water and observe the reaction.

Observation: 

Reaction with cold water:

Metals like sodium and potassium vigorously react with water to form its oxide and hydrogen gas. Their reaction is so violent that hydrogen gas catches fire immediately.

2Na(s) + 2H2O(l) ———-> 2NaOH(aq) + H2(g)

2K(s) + 2H2O(l) ———-> 2KOH(aq) + H2(g)

Reaction with hot water:

Calcium is less reactive than sodium and potassium with cold water. They react spontaneously and emit hydrogen bubbles. But, the reaction is not so violent and hydrogen gas does not catch fire.

Ca(s) + 2H2O(l) ———-> Ca(OH)2(aq) + H2(g)

Reaction with hot steam:

Metals like iron, zinc and aluminium do not react with cold or hot water. They react with steam to form corresponding hydroxide and hydrogen gas.

2Al(s) + 6H2O(l) ———-> 2Al(OH)3(aq) + 3H2(g)

No reaction: 

Metals like lead, copper, silver and gold do not react with any form of water.

Order of reactivity with water in descending order:

Na>K>Ca>Zn>Fe>Al

Inference/conclusion:

Metals react with water and form metal hydroxide. It produces hydrogen gas, which we can check by placing a match-stick near it.

Activity 3.11 

Brief procedure:

Activity 3.11 asks us to react to various metals with dilute hydrochloric acid and observe the reaction.

Observation: 

Metals react with dilute hydrochloric acid and form metal chlorides with the evolution of hydrogen gas.

Metal(s) + HCl(aq) ———–> Metal Chloride(aq) + H2(g)

E.g.

Ca(s) + 2HCl(aq) ————-> CaCl2(aq) + H2(g)

Order of reactivity:

Ca>Mg>Al>Zn>Fe>Pb>Cu

Reaction of metals with dilute hydrochloric acid

Temperature during the reaction: 

Experiment done at room temperature (25˚C).

Calcium: 40˚C

Zinc: 34˚C

Iron: 30˚C

Copper: 25˚C

Inference/conclusion:

Metals react with acids to form their salt. The process is exothermic and hydrogen gas is also produced.

Activity 3.12 

Brief procedure:

Activity 3.12 asks us to dip copper and iron nail into a salt solution of another metal and observe the reaction.

Observation: 

More reactive metals displace with metals from other salt solution and form corresponding salts.

e.g., Iron in a copper sulphate solution.

Explanation:

Iron is more reactive than copper. It displaces copper from copper sulphate and forms ferrous sulphate. Copper sulphate solution is blue while ferrous sulphate is green. So the solution turns green from blue.

Fe(s) + CuSO4(aq) ———–> FeSO4(aq) + Cu(s)

Note: The diplacement depend on reactivity series. A metal can displace a salt if the metal is higher in reactivity series.

Reactivity Series of Metals.

Activity 3.13

Brief procedure:

Activity wants us to find the various properties of various salts like physical nature, melting point, solubility, conduction of electricity.

Observation:

Salts of acids and bases are Hard; brittle; have a high melting point; soluble in water; insoluble in non-polar solvents like kerosene, benzene; conducts electricity.

Explanation:

Molecules of salt are closed together by the strong Ionic bond between anions and cations. This strong attraction gives a salt hard appearance, high melting and boiling point.

In water and other polar solvents, they form strong ionic bonds, so they are soluble in water. Non-polar solvents like organic solvents and kerosene do have polar bonds. A salt molecule, therefore, does not mix with such solvents. As a result, it sinks to the bottom.

In solution form molecules of salts are in ionic form. They move freely in the solution; therefore they conduct electricity.

Note: 

For any doubt, think about sodium chloride and solve the question.

Activity 3.14

Brief procedure:

Activity 3.14 asks us to experiment with iron nails in various conditions.

A. Iron dipped in water B. Nail dipped in water with some oil floating on water. C. Iron nail with calcium chloride.

Observation: 

Nails in test tube A got rusted in a few days. Nails in test tube B and C did not get rust.

Inference:

It shows water and air both are necessary to form rust.

Explanation:

Oxidation of iron metal with oxygen require high temperature. The other alternative is to use the hydration energy of water. The outer layer of iron nail reacts with oxygen in the presence of water to form its oxide.

4Fe(s) + 6H2O(l) + 3O2(g) ———-> 2Fe2O3*3H2O

Outer layer now scrapes off and give way to oxygen and moisture to the inner layer of iron. The process goes on until all iron convert into its oxide.

In the test tube, B oil prevents oxygen from dissolving in water. In the test tube C, calcium chloride acts as an absorbent and absorbs moisture present in it. So, Iron does not form rust in these test tubes.

Cls 9 Sci Chp 4 Structure Of The Atom

 Class 9 Science 

 Chapter 4 Structure Of The Atom 

Introduction

→ John Dalton considered atom to be an indivisible entity, but his concept had to be discarded at the end of nineteenth century, when scientists through experiments were able to find existence of charged (electrons and protons) and neutral particles (neutrons) in the atom. These particles were called the ‘Sub-atomic Particles’.

Discovery of Electrons – Cathode Rays (By J. J. Thomson)

→ Thomson explained presence of electrons by cathode rays experiment.

Facts about Electrons

→ Charge on electron = −1.6 × 10-19 C (C = Coloumb)(As calculated by Robert E. Millikan)

→ Mass of electron = 9.1 × 10-31 kg

Discovery of Protons – Anode Rays/Canal Rays (By E. Goldstein)

→ E. Goldstein by his famous anode rays/canal rays experiment was able to detect presence of positively charged particles called protons in the atom.Facts about Protons

→ Charge on proton = + 1.6 × 10-19 C

→ Mass of proton = 1.673 × 10-24 gm

i.e.,  Mass of proton ≅ 1840 × Mass of electron

Discovery of Neutrons (By J. Chadwick)

→ J. Chadwick bombarded lighter elements (like lithium, boron etc.) with α-particles and observed emission of new particles having zero charge but having mass equal to that of proton.

→ These particles were called ‘Neutron’ i.e., neutral particle of the atom.

→ Neutron are absent in Protium isotope of hydrogen atom.(1H1)

→ Since, mass of electrons are negligible as compared to that of proton and neutrons hence, sum of masses of protons and neutrons in an atom will compose its atomic mass.

Atomic Models

→ From the knowledge of existence of subatomic particles like electron, proton and neutron in an atom, various atomic models were proposed by different scientists.

• Some of the atomic models:

(i) Thomson’s Model of Atom

(ii) Rutherford’s Model of Atom

(iii) Bohr’s Model of Atom

→ The most trusted and scientifically established model of atom which is adopted these days is ‘Quantum Mechanical Model of Atom’. It will be dealt in higher classes.

Thomson’s Atomic Model

→ This model is often called the ‘Water Melon Model’.

→ In this model, Thomson predicted the presence of electrons inside positive sphere (made up of protons), just same as seeds of watermelon are embedded in red edible part of watermelon.

→ Although this model explained neutrality of atom but couldn’t able to explain other scientific experiments conducted on atom. Hence it was discarded.

Rutherford’s Atomic Model

→ In his famous ‘α-ray Scattering Experiment’, Rutherford bombarded α-ray (Helium nucleus 2He4) upon thin gold foil.

•  Observations made by Rutherford in his experiment:

(i) Most of α-particles passed through gold foil undeflected.

(ii) Some of the α-particles deflected by foil by small angles.

(iii) One out of every 12000 particles appeared to rebound.

• Conclusions made by Rutherford:

(i) Atom consists of predominantly empty space as most of α-particles passed through gold foil undeflected.

(ii) Atom contains centrally placed positively charged nucleus (carrying positively charged particles), because few α-particles suffered deflected and very few i.e., one in 12000 bounced back.

(iii) Since a minute fraction of α-particles suffered deflections and very few bounced back, this lead to conclusion that most of the space an atom is empty and the space occupied by nucleus is negligible compared to this empty space.

→ Size of nucleus was about 10-5 times that of size of atom.

(iv) Whole of the atomic mass concentrated in the nucleus.

• Features of Rutherford proposed model of atom:

(i) There is positively placed nucleus in an atom. Nearly all the mass resides in nucleus (Proton + Neutron).

(ii) Electrons revolves round the nucleus in well defined orbits.

(iii) Size of nucleus is very small compared to the size of atom.

Drawbacks of Rutherford’s Model (Unstability of Atom)

→ According to Rutherford, electrons revolve round the nucleus in well-defined orbits, but electrons being charged particles will lose their energy and finally will fall into the nucleus.

→ This will make atom highly unstable.

→ This was the major drawback of Rutherford which was unexplained by him.

→ To overcome drawbacks of Rutherford’s Model, Neil Bohr in 1912 proposed modified model of structure of atom.

Assumption made by Neil Bohr

→ Only certain special orbits known as discrete orbits of electrons are allowed inside the atom.

→ While revolving in discrete orbits, the electrons do not radiate energy.

→ Energy is emitted or absorbed by an atom only when an electron moves from one orbit to another.

Atomic Number

→ The total number of proton lying in the nucleus of any atom is called the atomic number.

→ Atomic number is denoted by ‘Z’.

→ Atomic number = no. of protons or a neutral atom, no. of protons and electrons are equal.

Mass Number

→ It is the sum of total number of protons and no. of neutrons lying in the nucleus of an atom.

→ It is denoted by ‘A’.

→ Mass number = no. of protons + no. neutrons

→ Representation of an atom: ZEA or AZE (E= symbol of an element)

Example: Calculate number of protons, electrons and neutrons for 17Cl35 or 3517Cl

Since Cl is neutral,

No. of electrons = no. of protons = 17

Mass no. of Cl = 35

No. of neutrons = 35 - 17 =18

Distribution Of Electrons In Various Shells

→ The distribution of electrons in various shells is done in accordance to ‘Bohr-Bury Scheme’.Bohr-Bury Scheme

(i) The filling of electrons in an atom is done in accordance to ‘2n2’, where ‘n’ is the number of shell and ‘2n2’ represents the total number of electrons that can be accommodated in that particular shell.

→ Maximum number of electrons that can be filled in particular shell.

ii) The outermost shell can’t hold more than 8 electrons, while second last shell can’t have more than 18 electrons, even though they may have capacity to hold more electrons.

Example: ‘Ca20’, the electron distribution will be :

Ca20 =  2(K), 8(L), 8(M), 2(N)

→ But Ca20 = 2, 8, 10 is wrong although ‘M’ shell can contain upto 18 electrons.

(iii) The outermost shell can’t hold more than 2 electrons and the penultimate shell can’t hold more than 8 electrons unless the preceding inner shell (antepenultimate shell) is filled completely obeying ‘2n2’ rule.

Some examples:

(i) Ka(19) = 2, 8, 8, 1

(ii) Al(13) = 2, 8, 3

(iii) F(9) = 2, 7

(iv) Ne(10) = 2, 8

(v) Na(11)= 2, 8, 1

Valence Shell and Valence Electrons

→ From Bohr-Bury sequence, we know that maximum number of electrons which can be accommodated in outermost shell is 8.

→ Every element has an urge to have 8 electrons in its outermost shell, in achieving 8 electrons an atom can either gain electrons or loose electrons.

→ The number of electrons lost or gained by an element in achieving 8 electrons in its outermost shell will be called its Valence.

→ For elements like H, He, Li, Be and B, these elements lose their outermost electron to achieve 2 electrons in their outermost shell. These elements will have valence in accordance to this act.

Isotopes

→ Isotopes are atoms of same elements having same atomic number and different mass numbers.

Example: Chlorine has two isotopes of mass numbers 35 and 37 respectively.

17Cl35, 17Cl37

Uses of isotopes

(i) Uranium isotope is used as fuel in nuclear rector.

(ii) Isotope of cobalt is useful in treatment of cancer.

(iii) An isotope of iodine is used in the treatment of goiter.

Isobars

→ Isobars are the atoms of those elements which have the same mass number but different atomic numbers are called isobars.

→ 20Ca40 and 18Ar40 have same mass number and different atomic number.

11Na24 and 12Mg24 are another examples.

Cls 10 Sci Chp 3 Solsn

 Class 10 Science 

 Chapter 3 Metals and Non-Metals 

 Solutions 

Intext Questions

Page number 40

1. Give an example of a metal which

(i) Is a liquid at room temperature?

(ii) Can be easily cut with a knife?

(iii) Is the best conductor of heat?

(iv) Is a poor conductor of heat?

Ans:

(i) Mercury

(ii) Sodium

(iii) Silver

(iv) Lead

2. Explain the meanings of malleable and ductile.

Ans:

> Metals which can be beaten to thin sheets are said to be malleable

> Metals which can be drawn into thin wires are said to be ductile

Page number 46

1. Why is sodium kept immersed in kerosene oil?

Ans:

to prevent its reaction with oxygen, moisture and carbon dioxide of aired to prevent accidental fires.

2. Write equations for the reactions of

(i) iron with steam

(ii) calcium and potassium with water

Ans:

(i) 3Fe(s) + 4H2O(g) → Fe3O4(s) + 4H2(g)

(ii) 

Ca(s) + 2H2O(I) → Ca(OH)2(aq) + H2(g)

2K(s) + 2H2O(I) → 2KOH(aq) + 2H2(g)

3. Samples of four metals A, B, C and D were taken and added to the following solution one by one. The results obtained have been tabulated as follows

Use the Table above to answer the following questions about metals A, B, C and D.

Which is the most reactive metal?

What would you observe if B is added to a solution of Copper (II) sulphate?

Arrange the metals A, B, C and D in the order of decreasing reactivity.

Ans:

(i) B is most reactive metal.

(ii) B will displace copper from copper sulphate.

(iii) Arrangement of metals in the order of decreasing reactivity B>A>C>D.

4. Which gas is produced when dilute hydrochloric acid is added to a reactive metal? Write the chemical reaction when iron reacts with dilute H2SO4.

Ans:

Hydrogen gas is liberated when dilute HCl is added to a reactive metal.

Fe(s) + H2SO4(aq) → FeSO4(aq) + H2(g)

5. What would you observe when zinc is added to a solution of iron (II) sulphate? Write the chemical reaction that takes place.

Ans:

Zinc is more reactive than iron. Therefore Zinc displaces Iron from its salt solution. The colour of ferrous sulphate is pale green, which turns colourless.

FeSO4 + Zn → ZnSO4 + Fe(s)

Page number 49

1. (i) Write the electron-dot structures for sodium oxygen and magnesium.

(ii) Show the formation of Na2O and MgO by the transfer of electrons.

(iii)What are the ions present in these compounds?

Ans:

(ii) Formation of Na2O and MgO:

(iii) In Na2O, ions present are Na+ and O2-.

In MgO, ions present are Mg2+ and O2-.

2. Why do ionic compounds have high melting points?

Ans:

Ionic compounds have strong electrostatic forces of attraction between the ions. Therefore, it requires a lot of energy to overcome these forces. That is why ionic compounds have high melting points.

Page number 53

1. Define the following terms.

(i) Mineral

(ii) Ore

(iii) Gangue

Ans:

(i) Mineral: The naturally occurring compounds of elements are known as Mineral.

(ii) Ore: Minerals from which metals can be extracted profitably are known as ores.

(iii) Gangue: The impurities present in the ore such as sand, rocks etc are non as gangue.

2. Name two metals which are found in nature in the free state

Ans: Gold and platinum

3. What chemical process is used for obtaining a metal from its oxide?

Ans:

Reduction process is used for obtaining a metal from its oxide.

For example, zinc oxide is reduced to metallic zinc by heating with carbon.

ZnO(s) + C(s) → Zn(s) + CO(g)

Page number 55

1. Metallic oxides of zinc, magnesium and copper were heated with the following metals

Ans:

A more reactive metal can displace a less reactive metal from its oxide. But out of zinc, magnesium, and copper metals, magnesium is the most reactive, zinc is less reactive whereas copper is the least reactive metal.

2. Which metals do not corrode easily?

Ans:

Gold and platinum

3. What are alloys?

Ans: 

An alloy is a homogeneous mixture of two or more metals, or a metal and a non-metal.

Exercise questions

1. Which of the following pairs will give displacement reactions?

(a) NaCl solution and copper metal

(b) MgCl2 solution and aluminium metal

(c) FeSO4 solution and silver metal

(d) AgNO3 solution and copper metal

Ans: (d) AgNO3 solution and copper metal

2. Which of the following methods is suitable for preventing an iron frying pan from rusting?

(a) Applying grease

(b) Applying paint.

(c) Applying a coating of zinc

(d) All the above.

Ans: (c) Applying a coating of zinc

3. An element reacts with oxygen to give a compound with a high melting point. This compound is also soluble in water. The element is likely to be

(a) calcium

(b) carbon

(c) silicon

(d) iron

Ans:  (a) Calcium.

4. Food cans are coated with tin and not with zinc because

(a) zinc is costlier than tin

(b) zinc has a higher melting point than tin

(c) zinc is less reactive than tin

(d) zinc is more reactive than tin.

Ans: (d) Zinc is more reactive than tin.

5. You are given a hammer, a battery, a bulb, wires and a switch.

(a) How could you use them to distinguish between samples of metals and non-metals?

(b) Assess the usefulness of these tests in distinguishing between metals and non-metals.

Ans:

a) 

> Metals can be beaten into thin sheets with a hammer without breaking.

> Non-metals break into pieces when hammered.

> Metals are malleable, while non-metals are non-melleable.

> When metals are connected into circuit and the bulb glows.

> When non-metals (like sulphur) are connected, the bulb does not light up at all.

> Metals are good conductors of electricity.

b)

The above tests are useful in distinguishing between metals and non-metals

6. What are amphoteric oxides? Give two examples of amphoteric oxides

Ans:

metal oxides that react wtih both acids and bases to form salt and water are called amphoteric oxides.

Ex: Aluminium oxide and zinc oxide are amphoteric in nature.

7. Name two metals which will displace hydrogen from dilute acids, and two metals which will not.

Ans:

> Iron and aluminium will displace hydrogen from dilute acids as they more reactive then hydrogen.

> Mercury and copper cannot displace hydrogen from dilute acids as they are less reactive than hydrogen.

8. In the electrolytic refining of a metal M, what would you take as the anode, the cathode and the electrolyte?

Ans:

Cathode – Pure metal

Anode – Impure metal

Electrolyte – Metal salt solution

9. Pratyush took sulphur powder on a spatula and heated it. He collected the gas evolved by inverting a test tube over it, as shown in figure below.

(a) What will be the action of gas on

(i) dry litmus paper?

(ii) moist litmus paper?

(b) Write a balanced chemical equation for the reaction taking place.

Ans:

a) When sulphur powder is burnt in the air sulphur-di-oxide is formed.

(i) Sulphur-di-oxide does not have any effect on dry litmus paper.

(ii) Sulphur-di-oxide turn the moist litmus paper from blue to red as contact of SO2 with water turns to sulfurous acid.

(b) S(s) + O2(g) → SO2(g)

SO2(g) + H2O →H2SO3

10. State two ways to prevent the rusting of iron.

Ans:

Ways to prevent rusting of iron are :

(a) By painting

(b) By galvanizing

11. What type of oxides are formed when non-metals combine with oxygen?

Ans:

Non-metals combine with oxygen to form acidic oxides or neutral oxides.

12. Give reasons

(a) Platinum, gold and silver are used to make jewellery.

(b) Sodium, potassium and lithium are stored under oil.

c) Aluminium is a highly reactive metal, yet it is used to make utensils for cooking.

(d) Carbonate and sulphide ores are usually converted into oxides during the process of extraction

Ans:

a) because these are malleable and ductile. These are highly resistant to corrosion.

b) Sodium, potassium, and lithium are very reactive metals and react very vigorously with air as well as water.

c) Aluminium forms a non-reactive layer of aluminium oxide on its surface. This layer prevents aluminium to react with other substances.

13. You must have seen tarnished copper vessels being cleaned with lemon or tamarind juice. Explain why these sour substances are effective in cleaning the vessels.

Ans:

The sour substances such as lemon or tamarind juice contain acids. These acids dissolve the coating of copper oxide or basic copper carbonate present on the surface of tarnished copper vessels and makes them shining red-brown again.

14. Differentiate between metal and non-metal on the basis of their chemical properties.

Ans:

Metal:

> Metals are electropositive.

> Oxides of metal are basic in nature.

> Metals form chlorides which are electrovalent or ionic compounds.

> They react with water to form oxides and hydroxides. Some metals react with cold water, some with hot water, and some with steam. 

Non-metal:

> Non-metals are electronegative.

> Oxides of non-metals are acidic in nature.

> Non-metals form chlorides which are covalent compounds.
> They do not react with water.

15. A man went door-to door posing as a goldsmith. He promised to bring back the glitter of old and dull gold ornaments. An unsuspecting lady gave a set of gold bangles to him which he dipped in a particular solution. The bangles sparkled like new but their weight was reduced drastically. The lady was upset but after a futile argument the man beat a hasty repeat. Can you play the detective to find out the nature of the solution he has used ?

Ans:

The solution he had used was Aqua regia. Aqua regia is Latin word which means ‘Royal Water’. It is the mixture of concentrated Hydrochloric acid and concentrated nitric acid in the ratio of 3:1. It is capable of dissolving metals like Gold and Platinum. Since the outer layer of the gold bangles is dissolved in aqua regia so their weight was reduced drastically.

16. Give reasons why copper is used to make hot water tanks and not steel (analloy of iron).

Ans:

> Copper is a better conductor of heat than steel.

> Copper does not corrode easily. But steel corrodes easily.

> Copper does not react with water at any temperature, whereas iron reacts with water on heating.

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Cls 9 Chp 5 Fundamental unit of Life

  Class 9 Science Notes  

  Chapter 5 Fundamental Unit of Life  

Introduction

• Cell is the structural and functional unit of life. It is the basic unit of life.

• It is discovered by Robert Hook in 1831 in cork slice with the help of primitive microscope.

• Leeuwenhoek (1674), discovered the free living cells in pond water with the improved microscope.

• Robert Brown discovered the nucleus in the cell in 1831.

• Purkinje coined the term ‘protoplasm’ for the fluid substance of the cell in 1839

The cell theory

• The theory that all the plants and animals are composed of cells and the cell is the basic unit of life, was presented by two biologists, Schleiden and Schwann.

• The cell theory was further expanded by Virchow by suggesting that all cells arise from pre-existing cells.

→ Types of organisms

• On the basis of no. of cells, organisms are of two types:

(i) Unicellular Organism

(ii) Multicellular Organism

(i) Unicellular Organism: These organisms are single celled which perform all the functions.

Example: Amoeba, paramecium, bacteria.

(ii) Multicellular Organism: Many cells grouped together to perform different function in the body  and also form various body parts.

Example: fungi, plants, animals.

• The shape and size of cell are different according to the kind of function they perform. There is division of labour in cells.

• Each cell has certain kind of cell organelles to perform different type of function like mitochondria for respiration.

→ Types of cells

• There are two types of cells:

(i) Prokaryotes  (ii) Eukaryotes

(i) Prokaryotes:

> Cells of organism lacks nuclear membrane.

> Nucleolus is absent.

> Single chromosomes. Single or multi chromosomesReproduction is always asexual.

Example: Bacteria, Blue green algae, etc.

(ii)Eukaryotes:

> Cells of organism have nuclear membrane.

> Nucleolus is present.

> Reproduction is both sexual and asexual.

Example: Fungi, Plant cell, Animal cell etc

Difference between Animal cell and Plant cell

Animal Cell:

> Cell wall is absent.

> Plastids are absent. 

> Centrioles are present.

> Golgi bodies are present.

> Vacuoles are absent. If present, they are small.

Plant Cell:

> Cell wall is present.

> Plastids are present

> Centrioles are absent.

> Golgi bodies are present and called dictyosome.

> Vacuoles are present and large in size.

Diffusion

• The spontaneous movement of a substance from a region of high concentration to the region of low concentration is called diffusion.

• Some substances like carbon dioxide or oxygen can move across the cell membrane by a process called diffusion. Cell also obtains nutrition from the environment.

Osmosis

• The movement of water molecules through selectively permeable membrane along the concentration gradient is called osmosis.

• Plant cell tend to obtain water through osmosis.

Hypotonic solution

If the medium surrounding the cell has a higher water concentration than the cell, the cell will gain water by osmosis. Such a solution is known as hypotonic solution.

isotonic solution

If the medium has exactly the same water concentration as the cell, there will be no net movement of water across the cell membrane. Such a solution is known as isotonic solution.

hypertonic solution

If the medium has a lower water concentration then the cell will lose water by osmosis. Such a solution is known as hypertonic solution.

Plasma membrane or Cell membrane

• This is the outermost covering of the cell that separates the contents of the cell from its external environment.

• The plasma membrane allows or permits the entry and exit of some materials in and out of the cell.

• It also prevents movement of some other materials. The cell membrane is called selectively permeable membrane.

• It is made up of lipid and protein.

→ Properties of Plasma mmembrane

• It is flexible (made up of organic molecules called lipids and proteins).

• Its flexibility enables cell to engulf in food and other from the external environment. This process is called endocytosis. Amoeba acquire food through this process.

→ Functions of Plasma membrane

• It permits the entry and exit of some materials in and out of the cell.

• It prevents movement of some other materials not required for the cell as it acts like selectively permeable membrane.

Cell Wall

• Cell wall is another rigid outer covering in addition to the plasma membrane found in plant cell. The cell wall lies outside the plasma membrane.

• The plant cell wall is mainly composed of cellulose. Cellulose is a complex substance which provides structural strength to plants.

→ Function of Cell Wall

• Cell walls permit the cells of plants, fungi and bacteria to withstand very dilute (hypotonic) external media without bursting.

• In such media the cells tend to take up water by osmosis. The cell swells, building up pressure against the cell wall. The wall exerts an equal pressure against the swollen cell.

• Because of cell wall, cells can withstand much greater changes in the surrounding medium than animal cells.

Plasmolysis

• When a living plant cell loses water through osmosis there is shrinkage or contraction of the contents of the cell away from the cell wall. This phenomenon is known as plasmolysis.

Nucleus

• It is called the brain of the cell as it controls all the activities of cell.

→ Composition of Nucleus

• The nucleus has a double layered covering called nuclear membrane.

• The nuclear membrane has pores which allow the transfer of material from inside the nucleus to the cytoplasm.

• The nucleus contains chromosomes, which are visible as rod-shaped structures only when the cell is about to divide.

→ Functions of chromosomes

• Chromosomes transfer the characters from parents to children in the form of DNA (Deoxyribo Nucleic Acid) molecules.

• Chromosomes are composed of DNA and protein.

Nucleoid

• In some organisms like bacteria, the nuclear region of the cell may be poorly defined due to the absence of a nuclear membrane.

• Such an undefined nuclear region containing only nucleic acids is called a nucleoid.

Cytoplasm

• The cytoplasm is the fluid content inside the plasma membrane.

• It also contains many specialised cell organelles. Each of these organelles performs a specific function for the cell.

→ Function of Cytoplasm

• It helps in exchange of material between cell organelles.

• It act as store of vital chemicals such as amino acid, glucose, vitamins and iron etc.

Endoplasmic Reticulum (ER)

• The endoplasmic reticulum (ER) is a large network of membrane-bound tubes and sheets.

• It is also made up of lipid and proteins.

→ Types of Endoplasmic Reticulum

(i) Rough endoplasmic reticulum (RER)(ii) Smooth endoplasmic reticulum (SER)

→ Functions of Endoplasmic Reticulum

• RER looks rough under a microscope because it has particles called ribosomes attached to its surface. The manufactured proteins are then sent to various places in the cell depending on need, using the ER.

• The SER helps in the manufacture of fat molecules, or lipids, important for cell function.

• Some of these proteins and lipids help in building the cell membrane. This process is known as membrane biogenesis.

Golgi Apparatus

•The golgi apparatus, first described by Camillo Golgi, consists of a system of membrane-bound vesicles arranged approximately, parallel to each other in stacks called cisterns.

• The material synthesised near the ER is packaged and dispatched to various targets inside and outside the cell through the Golgi apparatus.

• It’s function include the storage, modification and packages of products in vesicles. 

• It is also involved in the formation of lysosomes.

Lysosomes

• Lysosomes break foreign materials entering the cell, such as bacteria or food as well as old organelles into small pieces.

• They contain powerful digestive enzymes which are made in RER which is capable of breaking down all organic material made in RER.

• when the cell gets damaged, lysosomes may burst and the enzymes digest their own cell. Therefore, lysosomes are also known as the ‘suicide bags’ of a cell.

Mitochondria

• Mitochondria are known as powerhouses of the cell.

• The energy required for various chemical activities needed for life is released by mitochondria in the form of ATP [Adenosine Triphosphate] molecules.

• ATP is known as energy currency of the cell.

• Mitochondria have two membrane coverings instead of just one.

• The outer membrane is very porous while the inner membrane is deeply folded.

• They are able to make some of their own protein.

Plastids

• Plastids are present only in plant cells.

• There are three types of plastids:

(i) Chromoplasts (coloured plastids).

(ii) Leucoplasts (white or colourless plastids).

(iii) Chloroplasts (contains the pigment chlorophyll).

→ Structure of Plastids

• The internal organisation of the plastids consists of numerous membrane layers embedded in a material called the stroma.

• Plastids also have their own DNA and ribosomes like mitochondria and similar to its structure.

→ Function of Plastids

• Chloroplasts are important for photosynthesis in plants.

• Chloroplasts also contain various yellow or orange pigments in addition to chlorophyll.

• Leucoplasts are primarily organelles in which materials such as starch, oils and protein granules are stored.

Vacuoles

• Vacuoles are storage sacs for solid or liquid contents.

• They are small sized in animal cells while plant cells have very large vacuoles.

→ Function of vacuoles

• The central vacuole of some plant cells may occupy 50-90% of the cell volume.

• In plant cells vacuoles are full of cell sap and provide turgidity and rigidity to the cell.

• Many important substance in the life of the plant cell are stored in vacuoles which include amino acids, sugars, various organic acids and some proteins.

• In single-celled organisms like Amoeba, the food vacuole contains the food items that the Amoeba has consumed.

• In some unicellular organisms, specialised vacuoles also play important roles in expelling excess water and some wastes from the cell.