Chemistry For Class IX (New Book ) - Chapter No. 8-Chemical Reactivity - Short Questions And Answers

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Chapter No.8-Chemical Reactivity
Short Questions And Answers

SECTION- B: SHORT QUESTIONS:

1. Identify the elements as Metals, Non-metals and Metalloids from the following elements:-

Elements	Metals	Non-Metals	Metalloids
C, Ca, Sb, S, Sr, Si, K, R Ba, Ge	Ca (Calcium), Sr,  K (Potassium), Ba (Barium)	C (carbon), S (Sulphur),  R	Sb (Antimony), Si (Silicon), Ge (Germanium)

2. What are Alkali metals? Write names and symbols of alkali metals?
Ans: ALKALI METALS:

• Elements of group IA are called Alkali metals. This group also called lithium family.
• Their Valence shell contain one electron
• The electronic configuration of alkali metals is ns¹.
• On reaction they lose one electron and form univalent (momovalent) positive ion. e.g. Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺
• They are highly reactive metals.
• They have low melting point.

Names Of Alkali Metals With Symbols:
This group includes:

• Lithium (Li)
• Sodium (Na)
• Potassium (K)
• Rubidium (Rb)
• Cesium (Cs) and
• Francium (Fr).

3. What are Alkaline Earth Metals? Write names and symbols of Alkaline earth metals?
Ans: ALKALINE EARTH METALS:

• Elements of group II A are called Alkaline earth metals. This group also called Beryllium family.
• Their valance shell contain two electrons.
• Their electronic configuration of alkaline earth metals is ns²
• On reaction they lose two electrons and form divalent positive ions. e.g. Be⁺², Mg⁺², Ca⁺², Sr⁺², Ba⁺², Ra⁺²
• They show irregular Density, Melting and Boiling point.

Names Of Alkaline Earth Metals With Symbols:
This group includes:

• Beryllium (Be)
• Magnesium (Mg)
• Calcium (Ca)
• Strontium (Sr)
• Barium (Ba)
• Radium (Ra)

4. What are Halogens? Write names and symbols of Halogens?
Ans: HALOGENS:

• Halogen belongs to VII-A group
• Halogens exist in Molecular form.
• The reactivity of halogens decreases down the group because atomic size increases and electro negativity decreases down the group. Their valance shell contain seven electron. So they gain one electrons and form monovalent anion.
  Example:
  
  Cl+ e^- → Cl^-

Members Of Halogens Group:

• It consists of Fluorine (F), Chlorine (Cl), Bromine (Br), Iodine (I) and Astatine (At).
• Except Astatine (metalloid) all halogens are non-metals.
• Fluorine (F) and Chlorine (Cl) are gases, Bromine (Br) is liquid and Iodine (I) is solid at room temperature.

5. Write names and symbols of any three metalloids.
Ans: Metalloid With Their Symbols:

1. Boron (B),
2. Silicon (Si),
3. Germanium (Ge),
4. Arsenic (As),
5. Antimony (Sb),
6. Tellurium (Te),
7. Polonium (Po) and
8. Astatine (At)

(Note: write down any three names as mentioned in question)

6. Define following with examples:
1. Cation
2. Anion
Ans: CATIONS:
When an atom or a molecule loses electron then it changes into positively charged ion. These positive ions move towards cathode during electrolysis so they are termed as Cation.

x → x⁺ + e^-

Example:

• Group I A (Alkali Earth Metal) or Lithium Family lose one electron and form monovalent cation. e.g. Li⁺ , Na⁺ , K⁺ etc.
• Group II A(Alkaline Earth Metals) or Beryllium Family lose two electron and form divalent cation. e.g. Ca²⁺, Mg²⁺ etc.
• Group III A metals lose three electron and form trivalent cation. e.g: B³⁺, Al³⁺ etc

ANIONS:
When an atom or a molecule accept or gain electron then it changes into negatively charged ions. These negative ions move towards anode during electrolysis so they are termed as anions.

x + e^- → x^-

The number of negative charges on anion shows the excess number of electrons as compared to number of protons.
Example:

• Group VII A(Halogen Family) accept one electrons and form monovalent anion. e.g.
  
  Cl+ e^- → Cl^-
• Group VI A (Oxygen Family) accept two electrons and form divalent anion. e.g. O^2-, S^2-

7. Explain why alkali metals do not exists free in nature? OR Analyze why alkali metals are not found in the free state in nature.
Ans: ALKALI MATELS DO NOT EXIST FREE IN NATURE:
Group I A elements are alkali metals. Alkali matels are electro positive and electro positive character of metals increases down the group with increasing atomic size.
Alkali metals have large atomic size and low ionization potential (ionization energy) values. The nucleus force on valence shell is very weak so they can lose their valence electron easily. Hence they are highly reactive, highly electro positive, powerful reducing agents and cannot exist free in nature.
Example:

Al ⟶ Al³⁺ + 3e^-

8. Explain inertness of noble metals.
Ans: Inertness of Noble Metal:
Nobel metals are less electro positive so they are difficult to oxidize. They are placed in the zero group of periodic table. Their electronic configuration is ns²p⁶. Therefore they show no reaction with atmospheric gases and resist corrosion. This helps noble metals to maintain their appearance.
Due to inertness, noble metals like Ag, Au, Pt are used to make ornaments.

9. Write names and symbols of some noble metals.
Ans: Names Of Noble Metals With Symbols:

Words	Meanings
Gold (Aurum)	Au
Silver (Argentum)	Ag
Platinum	Pt
Iridium	Ir
Osmium	Os
Rhodium	Rh
Ruthenium	Ru
Palladium	Pd

10. Explain electronegative character of non-metals.
Ans: ELECTRONEGATIVE CHARACTERS OF NON-METALS:
A Non-metal has property to accept electron easily and form Anion. It is called electronegative character.

x + e^- → x^-

Electronegative character increases across the period because Atomic size decreases and nuclear charge density increases. It decreases down the group due to increasing Atomic size.
Example:
Halogens accept electrons easily due to their high electronegative character.

Cl+ e^- → Cl^-

Test Your self

1. Which metal is found in liquid state? Write down its position, properties and uses?
Ans: LIQUID METAL:
Mercury is the only metal found in liquid state at normal temperatures.
Position: It belongs to sixth period and III B group of modern periodic table.
Properties: It has lowest melting point among all metals.
Uses:

• It forms alloys with other metals which are known as amalgam.
  For example,
  (i) Tin amalgam is an alloy of tin and mercury.
  (ii) Its alloy with silver and tin is used as dental filling.
• Mercury is used in thermometer and barometer.
• Gaseous mercury is used in street light and fluorescence lamps.

2. Identify the alkaline earth metals from the following elements.
Bi, Br, Ba, B, Se, Si, Sb, Sr
Ans: Alkaline Earth Metals are:

• Ba (Barium)
• Sr (Strontium)

(As elements of group II A are alkaline earth metals.)

3. Write few properties of metals.
Ans: Properties Of Metals:

• The element which readily loses electron in reaction and easily form cation is termed as metal.
• A metal structure consists of metal ions joined by metallic bonds.
• Metals are good conductors of heat and electricity.
• They are Ductile, Strong, Lustrous, Malleable and Sonorous.
• Metals has low electro-negativity.
• They have high melting points.
• They are solid.
• Oxides of metals are basic in nature e.g. (Li2O, Na2O2 ,KO2 ,MgO).

4. Write some properties of non-metals.
Ans: Properties Of Non-Metals:

• Non-metals are the elements which have greater tendency to accept or gain electron in reaction and form anion are termed as non-metals."
• They are poor or nonconductors of heat and electricity.
• Non-metals are non malleable; non ductile, dull in appearance, non-sonorous.
• Non-Metals has high electro-negativity.
• They have low melting point.
• They are solids and gases. Bromine (Br) is the only non-metal found in liquid state.
• Oxides of non-metals are acidic in nature e.g. (CO2 , SO3 , NO2).

5. Write uses of baking soda, bleach and sodium nitrate.
Ans: Uses:
1. Baking Soda (Sodium bicarbonate NaHCO₃):
Uses:

• It is used in Baking Powder, Health Salt, Beverages.

2. Bleach (Sodium hypochlorite NaClO):
Uses:

• It is used as a bleaching and disinfecting agent.
• They are disinfectants for drinking water and waste water purification systems and swimming pools.

3. Chile saltpeter (sodium nitrate NaNO₃):
Uses:

• It is used as fertilizer and in Dynamite.

6. Enlist the uses of magnesium.
Ans: Uses Of Magnesium:

1. It is used in flares and photographic flash bulbs because it burns to produce brilliant white light.
2. Magnesium hydroxide are used as an Antacid.
3. It is used for manufacturing of Mobile Phones, Laptop and Tablet Computers because of light weight and electrical properties.
4. The use of Magnesium reduces the weight of vehicle by replacing steel components of a vehicle.
5. Magnesium alloys are used in aviation industry, space crafts and missile because they are light weight and remain stable at high temperature.
6. Magnesium can be changed into intricate (twisters, knotty) shapes, so it is used in tennis, rackets and handles of archery bows.
7. Magnesium is used in cathodic protection (CP) to protect underground pipeline from corrosion.

7. Write uses of Slaked lime, Gypsum and calcium tungsten.
Ans: Uses:
1. Slaked lime ( Calcium hydroxide Ca(OH)₂):
Uses:

• As soil conditioner, it is used in water treatment to reduce acidity.
• It is also used in steel industry to remove impurities from Iron ore.

2. Gypsum (Calcium sulphate dihydrate 2CaSO₄.H₂O):
Uses:

• It is used as component in construction of buildings.
• It is used medically in plaster for setting broken bones.

3. Calcium tungsten CaWO₄:
Uses:

• It is used in Luminous paints.

8. Define Soft metals with examples.
Ans: Soft Metals:
The metals which are scratched easily are called soft metals.
Example: Alkali metals like; Sodium(Na), Potassium (K) and Rubidium (Rb) are soft metals.

9. Define hard metals with examples.
Ans: Hard Metals:
Metals which show strong resistance towards scratching are called hard metals.
Example: Nickle (Ni), Iron (Fe), Tungsten(W) are hard metals.

10. Write melting point, boiling point, density and moh values of sodium and iron.
Ans: Melting point, Boiling point, Density and Moh values of Sodium and Iron

	Sodium	Iron
Melting Point	98 °C	1535 °C
Boiling Point	890 °C	2450 °C
Density	0.971 g/cm3	7.87 g/cm3
Moh Value	0.5	4.5

11. Write names and symbols of few noble metals?
Ans: See above Section "B" Q.9.

12. Why helmets of astronauts are coated with thin film of gold?
Ans: See below in Scientific Reasons, Q.2.

13. Why glass surface are coated with gold?
Ans: See below in Scientific Reasons, Q.3.

14. Why gold is used in jewelry?
Ans: It is used in Jewellery because it has very high luster, yellow colour and tarnish resistance.

15. Why platinum is used as catalytic converter in vehicles?
Ans: It is used as catalytic converter in vehicles. It helps the complete combustion of Hydrocarbons and reduces the emission of air pollutants.

16. Identify the VIII A group elements from the following:
N, Na, Ni, Ne, Ar, At, He.
Ans: VIII A Group Elements:
VIII A group elements are noble gases. These are:

• Ne (Neon)
• Ar (Argon)
• He (Helium)

17. Write names and symbols of Non metals of VA group elements.
Ans: Non-Metals VA Group Elements:
Non metals of VA group elements are:

• Nitrogen (N)
• Phosphorous (P)

18. Which group contain non metals in gaseous state only?
Ans: VIIIA group contain non-metals in gaseous state only.

More Short Questions from Text Book

Q.1: Define chemical reactivity?
Ans: CHEMICAL REACTIVITY:

"The property of substance to undergo chemical reaction with any material is called chemical reactivity."

Reactivity of metals depends upon its tendency to lose electron and that of non metals depends upon its tendency to accept electron.
Matter which undergoes chemical reactivity may be element, compound or mixture.

Example:
Medicines, plastics, glass, detergents etc are the products of chemical reactivity.

Q.2: Name three most abundant elements found in air, earth’s crust, Universe and Human Body.
Ans: IN AIR:
Most abundant elements found in air are:

1. Nitrogen (N)
2. Oxygen(O)
3. Argon (Ar)

IN EARTH"S CRUST:
Most abundant elements found in earth’s crust are:

1. Oxygen (O)
2. Silicon (Si)
3. Aluminum (Al)

IN UNIVERSE:
Most abundant elements found in Universe are:

1. Hydrogen
2. Helium
3. Oxygen

IN HUMAN BODY:
Most abundant elements found in Human Body are:

1. Oxygen
2. Carbon
3. Hydrogen

Q.3: How can Alkali and Alkaline earth metals be identified?
Ans: IDENTIFICATION OF ALKALI AND ALKALINE METALS:
Alkali and Alkaline earth metals can be identified by the flame test. On burning they produce coloured flames.

Elements	Symbols	Colour of Flame
Lithium	Li	Bright Crimson (Bright Red)
Sodium	Na	Golden Yellow
Potassium	K	Violet
Rubidium	Rb	Lilac (Dark Red)
Cesium	Cs	Bright Blue
Beryllium	Be	White
Magnesium	Mg	Bright White
Calcium	Ca	Brick Red
Strontium	Sr	Crimson Red
Barium	Ba	Green

Q.4: Name some common compounds of Sodium with their chemical names, formula and uses?
Ans: Some common compounds of Sodium with their formula and uses are mentioned below:

Common Name	Chemical name	Formula	Uses
Soda Ash	Sodium carbonate	Na2CO3	Used as water softener.
Baking Soda	Sodium  bicarbonate	NaHCO3	Used in Baking Powder, Health Salt, Beverages.
Table Salt	Sodium chloride	NaCl	Food Items.
Chile saltpeter	Sodium Nitrate	NaNO3	Used as fertilizer and in Dynamite.

Q.5: Name some common compounds of calcium with their chemical names, formula and uses?
Ans: Some common compounds of Calcium with their formula and uses are mentioned below:

Common Name	Chemical name	Formula	Uses
Slaked lime	Calcium hydroxide	Ca(OH)2:	As soil conditioner, used in water treatment to reduce acidity. Used in steel industry to remove impurities from Iron ore.
Gypsum	Calcium sulphate dihydrate	2CaSO4.H2O	It is used as component in construction of buildings. It is used medically in plaster for setting broken bones.
Bleaching Powder,	Calcium hypochlorite	Ca(OCl)2	It is used for sterilization of water in swimming pool.
Calcium tungsten	Calcium tungsten	CaWO4	It is used in Luminous paints.
Limestone	Calcium carbonate	CaCO3	As source of CO2, In Cement industry.

Q.6: What is “Calcium Light”?
Ans: CALCIUM LIGHT:
In past, musical halls, theaters stages, were lit by chemical called lime (CaO), using Oxy-Hydrogen flame. As a result bright light was produced also known as Calcium light.
Uses: This light increases the visibility of audience to enjoy the performance of Actor on stage.

Q.7: What is hardness of metal? Define soft and hard metals? Also write down the value of hardness of following metals on moh scale: Lithium, Sodium, Potassium, Rubidium, Iron and Tungsten.
Ans: HARDNESS OF METALS:
Metals may be soft or hard. The hardness of metal is the resistance of metal to be scratched.
Measurement of Hardness:
Hardness of metals and other material is measured by Moh scale.
Moh Scale is devised by Frederich Mohs in 1812. It is based on scratch resistance of different metals and other materials.
Example:
Hardness of plastic, Lead pencil is 1, and that of Diamond is 10 on Moh scale.

Values of Hardness of few metals on Moh scale

Metals	Moh Scale Value
Lithium (Li)	0.8
Sodium (Na)	0.5
Potassium (K)	0.4
Rubidium (Rb)	0.3
Cesium (Cs)	0.2
Nickel (Ni)	4
Iron (Fe)	4.5
Tungsten (W)	7.5

Q.8: Define amalgam with examples?
Ans: AMALGAM:
Mercury forms alloys with other metals which are known as amalgam.
For example,

• Tin amalgam is an alloy of tin and mercury.
• Its alloy with silver and tin is used as dental filling.

Q.9: How acid rain is caused?
Ans:ACID RAIN:
Non-metals form acidic oxides which react with water vapors of atmosphere and cause acid rain.

SO₂ + H₂O → H₂SO₃ Sulphurous Acid

SO₃ + H₂O → H₂SO₄ Sulphuric Acid

CO₂ + H₂O → H₂CO₃ Carbonic Acid

Q.10: How can artificial rain occur?
Ans: ARTIFICIAL RAIN:
Artificial Rain can occur through cloud seeding.
Dr. Vincent J. Schaefer in 1946 successfully created artificial clouds in a chilled chamber.

1. In this process chemicals like Silver Iodide (AgI) or Dry ice (Solid CO₂) are spread over clouds.
2.  As a result a super cooled water molecule condenses rapidly around these chemicals and forms ice crystals.
3. When these ice crystals grow big and become too heavy then they fell downward and change into rain.

Q.11: How does enamel prevents tooth from decay?
Ans: ENAMEL PROTECT TOOTH:
Enamel is the outer layer of our teeth it is mainly composed of calcium carbonate (CaCO₃) and hydroxy apatite [Ca₃(PO₄)₂] . Ca(OH)₂.
Fluoride (F) ions of toothpaste replaces hydroxide (OH^-) ions of hydroxy apatite and form flouro apatite. This replacement makes enamel more resistant against tooth decay.

Differences

Q.12: Differentiate between:

• Metals, non-metals and metalloids.
• Reactivity of Alkali and Alkaline Earth Metals

Ans: 1-Difference Between Metal, Non-Metal and Metalloid.

METALS	NON-METALS	METALLOIDS
Tend to lose electrons in reactions.	Tend to gain electrons in reactions with metals.	Intermediate properties of metals and non-metals
They form cations	They form anions	-
They are solids with high melting point.	They are gases or solids with low melting point.	-
Good conductors of heat and electricity.	Poor-conductors of heat and electricity	-
Ductile	Not ductile	-
Lustrous	Often have dull appearance	-
Malleable	Non-malleable	-
Sonorous	Non- sonorous	_
Metals has low electro-negativity	Non-Metals has high electro-negativity	-
Oxides of metals are basic in nature.  e.g. (Li2O, Na2O2 ,KO2 ,MgO).	Oxides of non-metals are acidic in nature. e.g. (CO2 , SO3 , NO2).	Oxides of metalloids may be acidic (B2O3 , SiO2) or amphoteric (AS2O3).
Example: All B group elements (Transition Metals). e.g Iron (Fe), Copper (Cu) etc, Group I A (Alkali metals). e.g: Li, Na, K etc. Group II A (Alkaline earth metal)s. e.g Be, Mg, Ca (Calcium) etc.	Example: H (Hydrogen), N (Nitrogen), O(Oxygen), F(Fluorine), Cl (Chlorine) and VIII A group non-metals are gases. Bromine (Br) is the only non-metal found in liquid state. S (Sulphur), P (Phosphorus), Se (Selenium), I (Iodine) are solids.	Example: Boron (B), Silicon (Si), Germanium (Ge), Arsenic (As), Antimony (Sb), Tellurium (Te), Polonium (Po) and Astatine (At) are metalloids.

Comparison Of Reactivity Of Alkali And Alkaline Earth Metals

OR

Difference Between Alkali And Alkaline Earth Metals

S.NO.	Alkali Metals (I A)	Alkaline Earth Metals (II A)
1.	They are highly reactive than (IIA) group elements due to low ionization energy.	They are less reactive than (IA) group elements due to high ionization energy.
2.	They form monovalent cation (M+)	They form divalent cation (M2+)
3.	They immediately tarnish in air and form metal oxide. K + O2 ⟶ KO2	They react with oxygen on heating. 2Mg + O ⟶ 2MgO
4.	They react violently with halogens. 2Na + Cl ⟶ 2NaCl	They react slowly with halogens. Ca + Cl2 ⟶ CaCl2
5.	They react with water vigorously at room temperature and form strong alkaline solution. 2K + 2H2O ⟶ 2KOH +H2	They react with water less vigorously and form alkaline solution. Mg + H2O ⟶ MgO+ H2 MgO + H2O ⟶ Mg(OH)2
4.	Their oxides and hydroxides are more basic than those of II A group elements.	Their oxides and hydroxides are less basic than those of IA group elements.
5.	They do not form metal carbides.	They form metal carbides on heating. Ca + 2C ⟶ CaC2

Q.13: Show how cations and anions are related to the terms metals and non-metals.
Ans: CATIONS RELATED TO METALS:
Metals have low electro-negativity. So they can easily remove electron from their outermost (Valance) shell.
Such element which readily loses electron in reaction form cation and termed as metal.
Example:

• All B group elements are metals and known as Transition Metals. e.g Iron (Fe), Copper (Cu), Zinc (Zn) etc.
• Some elements of A group are also metals.
• (i) Elements of group I A are called Alkali metals. e.g: Lithium (Li), Sodium (Na), Potassium (K), Rubidium (Rb), Cesium (Cs) and Francium (Fr). (ii) Elements of group II A are called Alkaline earth metals. e.g Beryllium (Be), Magnesium (Mg), Calcium (Ca), Strontium (Sr), Ba (Barium), Radium (Ra).

ANIONS RELATED TO NON-METALS:
Non-Metals have high electro-negativity. So the elements those have a greater tendency to accept or gain electron in reaction and form anion are termed as non-metals."
Examples:

• Most of the non-metals are gases For example: H (Hydrogen), N (Nitrogen), O(Oxygen), F(Fluorine), Cl (Chlorine) and VIIIA group non-metals are gases.
• Bromine (Br) is the only non-metal found in liquid state.
• Some non metals like S (Sulphur), P (Phosphorus), Se (Selenium), I (Iodine) are solids.

Q.14: Name some elements, which are found in uncombined state in nature.
Ans: Elements of group VIII A are inert gases and are found in uncombined state in nature. This group includes:
Helium(He), Neon(Ne), Argon(Ar), Krypton (Kr) Xenon(Xe) and Radon(Rn)

Scientific Reason:

1. Why do Two pieces of pure un-coated metals permanently stuck together in space?
Ans: Reason:
Two pieces of pure un-coated metals permanently stuck together in space because there is no oxygen in space and hence no oxidation reaction occurs. The oxidized layer on metals serves as a barrier and prevent adherence of metals.

2. Why helmets of astronauts are coated with thin film of gold?
Ans: Reason:

The helmet of Astronaut is coated with thin film of gold which reflect intense Solar radiation and protect eyes, skin of astronaut.

3. Why glass surface are coated with gold?
Ans: Reason:

Glass surface coated with gold will reflect solar radiations outward and keep the Buildings cool in summer. It also reflects internal heat inward and keeps the Building warm in winter.