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

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Chapter No.8-Chemical Reactivity
Detailed Questions And Answers

SECTION- C: DETAILED QUESTIONS:
1. Explain importance of Silver.
Ans: IMPORTANCE OR COMMERCIAL VALUE OF SILVER (Ag):
It is widely used in society.

1. Jewelry: It is used in Jewelry, decorative items and Silver tableware because it does not tarnish and maintain its silvery shiny appearance.
2. Mirror: It is used to make mirror because it is best reflector of visible light.
3. Compounds: Silver forms compounds of significant importance.
4. Detection Of Halogen: Silver Nitrate (AgNO₃ ) or Lunar caustic is used in detection of Halogen.
5. Photographic Film: Light sensitive material AgBr and AgI are used in Photographic films.

2. Explain importance of Gold.
Ans: IMPORTANCE OR COMMERCIAL VALUE OF GOLD (Au):
Gold has importance in our society.

1. Jewelry: It is used in Jewellery because it has very high luster, yellow colour and tarnish resistance.
2. Electronic Components: Gold is used in Electronic components because it is highly efficient conductor of current and cannot corrode.
   (a) Cables: Gold is used in connecting wires, connection strips, switches and relay contacts to make electronic devices highly reliable.
   (b) Electronic Devices:
   (i) Gold is used in cellphones, global positioning systems, Calculators etc.
   (ii) Gold is used in Laptop, Computers for rapid and accurate transmission of digital information.
3. Dentistry: It is used in dentistry because it is chemically inert, non-allergic and easy for dentist to work.
4. Space vehicles: Gold coated polyester films are used in space vehicles to reflect infrared radiation and stabilize the temperature of space vehicle.
5. Helmet Of Astronaut: The helmet of Astronaut is coated with thin film of gold which reflect intense Solar radiation and protect eyes, skin of astronaut.
6. Coating Of Glass: 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.
7. Awards And Trophies: Gold symbolizes purity, beauty and stability so it is used in making medals, trophies awards etc.

3. Explain the experiment to test Cl^- and I^- ions.
Ans: Test For Cl^-1:

Experiment	Observation	Result
Few ml of salt solution + dilute HNO3 + AgNO3	White ppt	Cl-1 may be present.
White ppt + NH4OH solution	White ppt soluble in NH4OH	Cl-1 Ion is present.

Test For I^-1:

Experiment	Observation	Result
Few ml of salt solution + dilute HNO3 + AgNO3	Yellow ppt	I-1 ion may be present.
Yellow ppt + NH4OH solution	Yellow ppt insoluble in excess NH4OH	I-1 Ion is present.

4. Explain Electropositive character of metals.
Ans: ELECTROPOSITIVE CHARACTERS OF METALS (Cation formation):
Metals are highly electro positive, due to this property they easily lose their valance shell electrons and form cations.
Cations:
When an atom or a molecule loses electron then it changes into positively charged ion known as Cation.
Example:

Al ⟶ Al³⁺ + 3e^-

Reactivity:
Electro positive character of metals increases down the group with increasing atomic size.
Alkali metals have large atomic size and low ionization potential 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.

5. Explain the position of Magnesium in periodic table and its importance. OR Describe the position of magnesium in Periodic Table, their simple properties and uses.
Ans: MAGNESIUM (Mg):
Position:

• It is 8 most abundant element found in earth's crust.
• Magnesium belongs to II-A group and 3^rd period of periodic table.

Properties:
Physical properties:

• It is a grey-white metal.
• Its name is derived from Magnesia, a district in Greece.
• It melts at 650 °C and boils at 1090 °C.

Chemical Properties:
1. Reaction With Water:
Magnesium reacts violently with water and releases Hydrogen gas.

Mg + 2H₂ O → Mg (OH)₂ + H₂

Magnesium fire cannot be extinguished with water because H₂ gas is highly flammable and intensifies the fire. Magnesium fire can be extinguished by using dry sand.

Uses:

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 tenis, rackets and handles of archery bows.
7. Magnesium is used in cathodic protection (CP) to protect underground pipeline from corrosions.

6. Explain the position of Sodium in periodic table and its importance. Also write down its properties. OR Describe the position of sodium in Periodic Table, its simple properties and uses?
Ans: SODIUM (Na):
Position:

• It is sixth most abundant element and constitutes 2.87% of earth's crust.
• It belongs to I A group and 3^rd period of periodic table.

Properties:
Physical Properties:

1. Sodium is silvery white alkali metal.
2. It melts at 97.8 °C and boils at 881.4 °C.
3. It is soft and can be cut with Knife due to weak metallic bonding between their atoms.

Chemical Properties:

1. Reaction with water:
   It violently reacts with H²O water and form Sodium Hydroxide (NaOH) and Hydrogen (H₂) gas, so it is kept in kerosene oil to prevent its reaction with moisture.
   
   2Na + 2H₂O ⟶ 2NaOH + H₂
   
   
2. Reaction With Oxygen:
   Sodium metal has shining surface but its appearance becomes dull due to action of air.
   
   2Na + O₂ ⟶ Na₂O₂
   
   
3. Reaction With Halogens:
   Sodium reacts with halogens to form sodium halide.
   
   2Na + Br₂ ⟶ 2NaBr
   
   
4. Reaction With Acid:
   Sodium reacts with sulphuric acid to form H₂ gas.
   
   2Na + H₂SO₄ ⟶ Na₂SO₄ + H₂

Uses:

1. It is an excellent heat transfer fluid so its used as coolent in nuclear reactors.
2. It is used in Detergent preparation.
3. It is used as Street lights and gives yellow colour.
4. It is used as Reducing agent in the extraction of Calcium, Zirconium and Titanium.
5. Sodium form useful compounds, such as
   (i) Soda ash (Na₂CO₃) Used as water softener.
   (ii) Baking Soda (NaHCO₃) Used in Baking Powder, Health Salt, Beverages
   (iii) Table Salt (NaCl): Food Items.
   (iv) Sodium Nitrate (NaNO₃): Used as fertilizer and in Dynamite

7. Arrange the following Halogen Acids in increasing order of their Acidic strength: HBr, HCI, HI, HF.
Ans: The Acidic strength of Halogen Acid decreases in the following order:

HI > HBr > HCl > HF

• HI is very strong acid because HI easily breaks up and forms H⁺ Ion in water due to weak Covalent Bonding.
• HF is very weak acid because it has strong Covalent Bonding so it does not break up easily to form H⁺ Ion in water.

8. 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^-

9. Differentiate between sodium and iron as soft and hard metals. or Differentiate between soft and hard metals (Iron and Sodium).
Ans: Difference Between Soft And Hard Metals (Iron and Sodium):
Soft and hard metals can be differentiated with reference to sodium (Na) and iron (Fe) as follows:

S.NO.	Sodium	Iron
1.	It is a soft metal of group I A.	It is a hard metal VIII B
2.	It has large atomic size.	It has smaller ionic radii.
3.	It has low value (0.5) on moh scale.	It has high value (4.5) on moh scale.
4.	It has weak metallic bonding so it is a soft metal	It has strong metallic bonding so it is hard metal.
5.	It can be cut easily with knife.	It is hammered to form sheets and wires.
6.	It is light due to its low density (0.971 g/cm3).	It is heavier metal due to its high density (7.87 g/cm3 ).
7.	It has low melting and boiling point values: (melting point = 98 °C,  boiling point = 890 °C)	It has high melting and boiling point values: (melting point = 1535 °C, boiling point = 2450 °C)

Q.10: Discuss the reactivity of Halogen? OR Compile some important reactions of halogens.
Ans: REACTIVITY OF HALOGENS:
Halogen belongs to VII-A group and consists of:

1. Fluorine (F),
2. Chlorine (Cl),
3. Bromine (Br),
4. Iodine (I) and
5. Astatine (At).

Halogens exist in Molecular form. The reactivity of halogens decreases down the group because atomic size increases and electro negativity decreases down the group.

1. Act As Oxidizing Agent:
Halogens act as oxidizing agent, because they easily accept electron.

2Na + Cl₂ → 2NaCl

2K + l₂ → 2Kl

Power of Halogens as oxidizing agent decreases in the following order:

F₂ > Cl₂ > Br₂ > I₂

It means Fluorine can displace other Halogens due to its highest oxidizing power.

2. Highly reactive Halogens Replace Less Reactive halogens:
More reactive Halogen can displace less reactive Halogen form a solution of its salt.
Example:

• 2KI + Cl₂ → 2KCl + I₂
  Chlorine is more reactive Halogen than Iodine so Chlorine displaces Iodine. The mixture turns reddish brown due to liberation of Iodine.
  
  
• 2KCl + F₂ → 2KF + Cl₂
  
  
• 2KBr + F₂ → 2KF + Br₂

3. Reaction With Hydrogen:
Reaction of Hydrogen with Halogen form Halogen acid.

H₂ + X₂ ⟶ 2HX

Where,

• (X₂ = F₂, Cl₂, Br₂, I₂)
• (HX = HF, HCl, HBr, HI)

The Acidic strength of Halogen Acid decreases in the following order:

HI > HBr > HCl > HF

• HI is very strong acid because HI easily breaks up and forms H⁺ Ion in water due to weak Covalent Bonding.
• HF is very weak acid because it has strong Covalent Bonding so it does not break up easily to form H⁺ Ion in water.
• H⁺ Ions reacts with water molecule to forms Hydronium (H₃O )⁺

More Questions From Text Book

Q.1: Define element? What are the different type of elements Or Classifying the type of elements into metals, non-metals and metalloids.?
Ans: ELEMENT:
An element is always composed of like atoms.
Example:
Hydrogen (H₂), Carbon (C), Oxygen (O₂)

Types of elements:
Elements are further divided into:

• Metals,
• Non-metals and
• Metalloids

METALS:
"The element which readily loses electron in reaction and easily form cation is termed as metal."
Properties:

• 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 have low electro-negativity.
• They have high melting points.
• They are solid.
• Oxides of metals are basic in nature e.g. (Li₂O, Na₂O₂ ,KO₂ ,MgO).

Examples:

• 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).

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."

Non-metals are placed at upper right portion of periodic table.
Properties:

• They are poor or nonconductors of heat and electricity.
• Non-metals are non malleable; non ductile, dull in appearance, non-sonorous.
• Non-Metals have high electro-negativity.
• They have low melting point.
• They are solids and gases.
• Oxides of non-metals are acidic in nature e.g. (CO₂ , SO₃ , NO₂).

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.

METALLOIDS:

"Elements having intermediate properties of metals and non-metals. are termed as metalloids."

Properties:

• Oxides of metalloids may be acidic (B₂O₃ , SiO₂) or amphoteric (AS₂O₃).

Example:

• Boron (B), Silicon (Si), Germanium (Ge), Arsenic (As), Antimony (Sb), Tellurium (Te), Polonium (Po) and Astatine (At) are metalloids.

Q.2: Define ionization energy? Explain the ionization energy of alkali and alkaline earth metals?
Ans: IONIZATION ENERGY:
The removal of electron from an element requires energy which is known as Ionization Energy or Ionization Potential.

Atom + Energy ⟶ Cation + e^-

Ionization energies values decreases with increasing atomic size and vice versa.
Unit:
Ionization Potential Valence or unit of ionization energy is Kj/mole.

Ionization Energy of Alkali and Alkaline Earth Metal:
The Alkali metals and Alkaline earth metals show increasing trend of reactivity down the group because their atomic size increases down the group. Alkali Metals and Alkaline earth metals have low values of Ionization Energies due to which they easily lose their valence electron and form Cation. Thus they are highly reactive.

Alkali Metals Are Reactive Than Alkaline Earth Metals:
Since Alkali metals have low Ionization Energy values than Alkaline earth metals, so Alkali metals are highly reactive than Alkaline earth metals.

Q.3: How magnesium is used in cathodic protection (CP).
Ans: Cathodic Protection Of Magnesium:
Magnesium is easily oxidized as compared to iron so magnesium is used as anode and underground metallic pipelines become cathode to protect from corrosion.
Following reaction take place

Mg ⟶ Mg₂₊ + 2e^- (Oxidation) (At Anode)

O₂ + 4H⁺ + 4e^- ⟶ 2H₂O (Reduction) (At Cathode)

Q.4: Describe the position of calcium in Periodic Table, their simple properties and uses.
Ans: CALCIUM (Ca):
Position:

• It is 5^th abundant metal in earth's crust.
• It belongs to II A group and 4^th period.

Properties:
Physical Properties:

1. It is silvery white soft metal.
2. It melts at 851 °C and boils at 1484 °C.

Uses:

1. Calcium is essential for healthy teeth and bones.
2. Calcium forms useful compounds, such as:
   (i) Slaked lime Ca(OH)₂: As soil conditioner, used in water treatment to reduce acidity. Used in steel industry to remove impurities from Iron ore.
   (ii) Gypsum 2CaSO₄.H₂O: It is used as component in construction of buildings. It is used medically in plaster for setting broken bones.
   (iii) Calcium hypochlorite Ca(OCl)₂: It is used for sterilization of water in swimming pool.
   (iv) Calcium tungsten CaWO₄: It is used in Luminous paints.
   (v) Limestone CaCO₃: As source of CO₂, In Cement industry.

Q.5: Describe the commercial value of Platinum.
Ans: IMPORTANCE OR COMMERCIAL VALUE OF PLATINUM (Pt):

1. It is a silvery white corrosion resistance metal.
2. It is paramagnetic transition metal.
3. It is used in chemical reactions as catalyst.
   Reaction:
   It is used as catalytic converter in vehicles. It helps the complete combustion of Hydrocarbons and reduces the emission of air pollutants.
4. Price of precious metal is fixed according to its weight. Its density is more than Gold. So it is more expensive than Gold.

Q.6: Write down the qualitative analysis to identify the following cations like Zn⁺², Mg⁺², NH₄⁺¹, Ca⁺² and Ba⁺².

OR

Explain the experiment to test following cations: Zn⁺², Mg⁺², NH₄⁺¹, Ca⁺² and Ba⁺².

Ans: Qualitative analysis of Cations:

1. Test For Zn²⁺:

Experiment	Observation	Result
Salt Solution + NH4OH solution.	White ppt	Zn2+may be present
White ppt + excess NH4OH or NaOH solution.	White ppt is dissolved and form clear solution.	Zn2+ion is present .

2. Test For Mg⁺²:

Experiment	Observation	Result
Salt Solution + NaOH or NH40H solution.	White ppt	Mg2+may be present
White ppt + excess NH4OH / NaOH solution.	White ppt insoluble in excess of NaOH or NH4OH	Mg2+ion is present .

3. Test For NH₄⁺¹:

Experiment	Observation	Result
Portion of Aqueous solution of salt + NaOH solution warm	Pungent of NH3 Gas release	NH4+ Ion is present

4. Test For Ba⁺²:

Experiment	Observation	Result
Heat Nichrome wire until flame is no longer coloured.	Apple Green colour flame	Ba2+ is present

5. Test For Ca⁺²:

Experiment	Observation	Result
Dip the loop of wire into water and then in unknown salt. Heat the wire on flame.	Brick Red colour flame	Ca2+ is present

Q.7: Write down the qualitative analysis to identify the following anions like CO₃^-2, Cl^-, I_-⁺¹, SO₄^2- and NO₂^-.

OR

Explain the experiment to test following anions:
CO₃^-2, Cl^-, I_-⁺¹, SO₄^2- and NO₂^-.
Ans: Qualitative Analysis Of Anions:

1. Test For CO₃^-2:

Experiment	Observation	Result
Sample of Solid + Dilute Mineral Acid	Bubbles comes out which turns lime water milky.	CO3-2 Ion is present

2. Test For Cl^-1:

Experiment	Observation	Result
Few ml of salt solution + dilute HNO3 + AgNO3	White ppt	Cl-1 may be present.
White ppt + NH4OH solution	White ppt soluble in NH4OH	Cl-1 Ion is present.

3. Test For I^-1:

Experiment	Observation	Result
Few ml of salt solution + dilute HNO3 + AgNO3	Yellow ppt	I-1 ion may be present.
Yellow ppt + NH4OH solution	Yellow ppt insoluble in excess NH4OH	I-1 Ion is present.

4. Test For SO₄^2-:

Experiment	Observation	Result
Few ml of Sample + dilute HCl + few drops of BaCl2 Or Few drops of Sample of dilute HCI + few drops of lead nitrate Pb (NO3)2 soultion	White ppt	SO42- ion may be present.
White ppt + dilute HCl	White ppt insoluble in excess HCl	SO42- Ion is present.

5. Test For NO₂^-:

Experiment	Observation	Result
Small amount of salt + few drops of dilute H2SO4 solution	Reddish Brown vapours evolve	NO2- ion is present.

Q.8: Draw flow chart diagram of classification of metals, non-metals and metalloids.
Ans: FLOW CHART: