Chemistry (English And Urdu) - Solved Model Paper 2022 - For Class IX (Science Group)

 GO TO INDEX
Chemistry (Compulsory)
Solved Model Paper 2022
For Class IX (Science Group)

SOLUTION

Section 'B"

Q.2: Write down three differences between Polar and Non Polar Compounds
Ans: Difference Between Polar and Non Polar Compounds

S.NO.	Polar Compounds	Non Polar Compounds
1.	Polar covalent compounds are soluble in water.	Non polar covalent compounds are generally insoluble in water.
2.	Polar covalent compounds usually conduct electricity due to the formation of ions with water.	Non-polar covalent compounds do not conduct electricity in the solid, molten or aqueous solution.
3.	Polar covalent compounds insoluble in non-polar solvent.	Non-polar covalent compounds are soluble in non-polar solvent like petrol, benzene etc.
4.	Few examples of polar covalent compounds are H2SO4, H2O, HCl, HF, HBr, HI	Few examples of non-polar covalent compounds are CO2, CH4, C2H6.

Q.9: 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:
  i. Fluorine (F)
  ii. Chlorine (Cl)
  iii. Bromine (Br)
  iv. Iodine (I) and
  v. 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.

1. Define oxidation, reduction reactions with examples.
Ans: Oxidation and reduction reactions OR Redox reactions:
Oxidation and reduction reactions are electrochemical reactions. They are also called redox reaxtion. In electrochemistry oxidation and reduction reactions involve transfer of electrons.

OXIDATION REACTION:
(i) In terms of loss or gain of oxygen or hydrogen:
"Oxidation may involve introduction of oxygen or removal of Hydrogen from a chemical substance."
Example:

C + O₂ ⟶ CO₂ (burning of coal)

2C₈H₁₆ + 25O₂ ⟶ 16CO₂ + 18H₂O (combustion of octane)

N₂H₄ + O₂ ⟶ N₂ +2H₂O (removal of Hydrogen from Hydrazine)

(ii) In terms of loss or gain of electrons:
"The electrochemical reaction in which atom molecule or ion loses electron and its oxidation number increases is called oxidation reaction."
Example:

Cu ⟶ Cu⁺⁺ + 2e^- (Oxidation reaction)

REDUCTION REACTION:
(i) In terms of loss or gain of oxygen or hydrogen:
"Reduction may involve addition of Hydrogen or removal of oxygen from a chemical substance."
Example:

CuO + C ⟶ Cu + CO (reduction of copper oxide)

Fe₂O₃ 2Al ⟶ Al₂O₃ + 2Fe + Heat (Reduction of Iron oxide)

(ii) In terms of loss or gain of electrons:
"The electrochemical reaction in which atoms, molecule or ion accepts electron and its oxidation number decreases is called reduction reaction."
Example:

S + 2e^- ⟶ S^2- (Reduction reaction)

Section 'C'

Q.14: Write any four comparison of the characteristics of Solution, Suspension and Colloid.
Ans: Ans: Difference (Comparison) of the characteristics of Solution, Suspension and Colloid.

S.NO.	Solution	Suspension	Colloid
1.	Particle size less than 1	Particle size greater than 1000 nm	Particle size 1 to 100 nm
2.	Homogeneous (particles dissolve uniformly)	Heterogeneous (particles settle down after sometimes)	Homogeneous and heterogeneous (Particles do not settle down for a long time)
3.	Particles cannot be distinctly seen with the naked eye.	Particles are big enough but can be seen with naked eyes.	Colloidal particles cannot be seen with the naked eye but can be seen through ultra microscope.
4.	Clear, transparent and homogeneous.	Cloudy, but uniform and homogeneous	Cloudy, heterogeneous, at least two substances visible.
5.	Transparent but often colored.	Translucent and often opaque but can be transparent	Often opaque, but can be transparent.
6.	Cannot be separated	Cannot be separated	Can be separated easily.
7.	Do not scatter light	Scatter light, but are not transparent	Scatter light (Tyndall effect)
8.	Particles can pass through filter paper	Particles pass through filter paper.	Particles do not pass through filter paper.

(Note: write down any four differences as mentioned in question)

Q.16: What is co-ordinate covalent bond? Explain it with examples?
Ans: Coordinate Covalent Bond or Dative Covalent Bond:
Co-ordinate covalent bond is a special type of covalent bond. Each atom contributes one electron to form a covalent bond. However, covalent bond can be formed between two atoms even when only one of the atoms contributes both electrons constituting the covalent bond. As a result the bond has a partial (partly) ionic characters. Such a bond is called as a coordinate covalent bond or dative bond.
Definition:
Thus, we can define a coordinate covalent bond as:

"The type of bond in which bond pair of electrons is contributed by one atom only, is called coordinate covalent or dative covalent bond."

Concept of donor and acceptor:
The atom that donates the electron pair is called the donor and the other atom which accepts the electron pair is called acceptor. A coordinate covalent bond is represented by an arrow (⟶) pointing towards the atom which accepts the electron pair. The pair of unshared valance electrons possessed by the donor is called a lone pair.

Nature Of Coordinate Covalent Bond or Dative Covalent Bond:
Once a bond is formed, there is no difference between the dative covalent and ordinary covalent bonds in reality. The only difference between the two is a mode of formation. Due to their covalent nature of bond formation, the properties of these compounds are similar to those of covalent compounds.

Examples:
A few examples of formation of a coordinate covalent bond are given as under:
1. Ammonium Chloride:
The reaction between ammonia and hydrogen chloride involves the formation of a dative bond between N atom in NH₃ containing lone pairs and H⁺ ion from HCl. When ammonia reacts with hydrogen ions (H⁺) in an aqueous solution of an acid, the hydrogen ion is attracted to the lone pair and a coordinate covalent bond is formed.

2. Hydronium Ion:
When hydrogen chloride dissolves in water, hydrogen ion is attracted to the lone pair of electrons which is available on oxygen and hydronium ion is formed as shown below:

OR

Q.16: What is electroplating? How a steel spoon can be electroplated with Tin. Explain with a labelled diagram and electrode reactions? 
Ans: ELECTROPLATING (METALLIC COATING):
All metals can be protected from corrosion by coating its surface with other metal like tin (Sn) or zinc (Zn). The coating of metal at the surface of other metal by electrolytic process is called electroplating.

OR

The process of deposition of metal at the surface of other metal through electrolysis is called electroplating.
Example: Metals like iron can be electroplated with chromium (Cr), Nickle (Ni) and silver (Ag).

Tin Plating On A Steel Spoon:

• Electrolyte:
  Steel spoon can be tin plated by using acidified tin sulphate as electrolyte.
• Electrodes:
  Anode: Tin (Sn) metal is used as anode.
  Cathode: Steel spoon is used as cathode.

Process:

• When current passes through electrolyte tin ions (Sn+2) deposits at cathode as tin (Sn) metal. Tin (Sn) electrode, is then changes into tin ion (Sn2+).
  
  SnSO₄ ⇌ Sn⁺⁺ + SO₄
• Reaction At Anode:
  
  Sn ⟶ Sn⁺⁺ + 2e^- (Oxidation)
• Reaction At Cathode:
  
  Sn⁺⁺ + 2e^- ⟶ Sn (Reduction)

Click Here For Chemistry Practicals