Chemistry I - For Class IX (Science) - Solved Comprehensive Papers 2025 - By Practical Center

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Class IX
Chemistry I
Comprehensive Paper 2025

By Practical Center

SOLUTION
SECTION 'C'

Q.18: Define solubility. Write the name of factors affecting solubility and the general principle of solubility?
Ans: SOLUBILITY:
Solubility is defined as the maximum quantity of solute that can be dissolved in 100 grams of solvent to prepare saturated solution at a particular temperature. Different substances have different capability to dissolve in the same solvent at a particular temperature.

FACTORS EFFECTING SOLUBILITY:
1. Nature Of Solute and Solvent
2. Solute-solvent interaction
3. Temperature

GENERAL PRINCIPLE OF SOLUBILITY:

1. The general principle of solubility is "Like dissolves like'. Its mean that two substances with similar intermolecular forces are likely to be soluble in one another. It has been observed that:
   o Ionic and polar solute dissolved in polar solvents. For example, No,CO₃, sugar and alcohol are polar and dissolved in water because water is also polar.
   o Nonpolar solute dissolved in non-polar solvents. Such as oil and paints are non-polar, they are dissolved in ether as both are non-polar. Similarly, waxes and fats dissolve in benzene and not in water.
   o Nonpolar compounds are not soluble in polar solvents (water). For example, oil, petrol, benzene are non-polar, they are not dissolved in water because water is polar.
< li>Solute-solvent interaction
2. Temperature

Q.19: Define and describe the structure with labelled diagram. Also give working of Dry Cell OR Car Battery.
Ans: DRY CELL:
It is also known as Leclanche cell. It is a type of primary cell (non-rechargeable cell) which produce electricity using redox reaction between their chemical substances placed in it.
It converts chemical energy into electrical energy. It is used in torches, clocks, calculators etc.

Construction:
Electrodes:

• Anode: Dry cell has Zinc (Zn) case. It uses zinc as anode. The zinc case acts as negative plate and negative terminal.
• Cathode: A graphite(C) rod through the center of the cell serves as the cathode. The positive terminal is on the central-graphite rod.

A mixture of Manganese dioxide (MnO₂) and graphite powder is packed around the graphite rod. A copper cap is fixed on the top of the carbon (graphite) rod for conduction of electricity.

Electrolytes:
Aqueous ammonium chloride (NH₄Cl) or zinc chloride (ZnCl₂) uses as electrolyte.

Working:
Zinc and graphite are then connected by a metal wire, electric current flows. As a result following chemical reactions take place.
Reaction At Anode:

Zn ⟶ Zn⁺² + 2e^-

Zn⁺²_(aq) ions go into the moist paste and electrons are left behind on the zinc case.

Reaction At Cathode:
It is a complex reaction

2NH₄⁺ + 2MnO₂ + 2e^- ⟶ Mn₂O₂ + 2NH₃ + H₂O

Voltage: It produces a potential of 1.5 volt.

OR

BATTERIES:
A battery is a device which produces electricity through electro chemical reactions. A battery consists of group of galvanic cells connected in a series. It stores more energy and supplies large (higher) current.
Batteries are classified as primary (non rechargeable) and secondary (rechargeable) batteries.
Examples: of batteries include:

• Dry cell, lead storage battery, mercury battery etc.
• We use lot of electrical devices having batteries as a source of electricity.
• Scientist are working for enhancing high energy, safety, cycle ability of batteries for mobile phones, transportation, computer technology etc.

LEAD STORAGE BATTERY:
Construction:

1. Lead storage battery is an example of secondary cell in which chemical changes can be reversed. It is used in motor vehicles (automobiles).
2. It has several (six) voltaic cells connected in series.
3. Electrodes:
   It contains two types of plates:
   (i) Anode: lead plates which serve as anode (negative plate) and
   (ii) Cathode: lead oxide (PbO₂) plate which acts as cathode (positive plate).
   These plates are separated by a n inert material (wood or glass fibre).
4. Electrolyte:
   These electrodes are immersed in electrolytic solution of dilute sulphuric acid (H₂SO₄). The acid acts as a source of H⁺ ions and SO₄^2- ions.

Working Of Lead Battery:
It consist of two processes:

1. Discharging Process
2. Charging Process

1. Discharging Process:

• During discharge the chemical energy is converted into electrical energy.
• When two electrodes are connected to external circuit, the lead storage battery produces electricity by discharging.
• The battery discharges or released or give out electrons at the anode flow through the external circuit to the cathode.
• As a result the lead and lead oxide on the electrodes are slowly start converted to soft lead sulphate.
• The reaction dilutes the acid because water is also produced.
• The electrode reactions that occur during discharge are:
  At Anode:
  
  Pb_(s) + SO₄^2-_(aq) ⟶ PbSO_4(s) + 2e^- (Oxidation)
  
  At cathode:
  
  PbO_2(s) + SO₄^2-_(aq) + 4H⁺_(aq) + 2e^- ⟶ PbSO_4(s) + 2H₂O_(l) (Reduction)

Recharging Process:

• During recharging, electrical energy is converted into chemical energy, and the storage battery act as the electrolytic cell.
• A lead- storage battery can be charged, when it is connected to an external source of electrical energy (i.e. battery charger).
• Electrons are pushed back through the battery (secondary cell).
• This reserve the electrodes reactions; lead and lead oxide are built up to on the respective electrodes again. So these are the materials of fully charges cells.

Overall Process:
Chemical changes during charging and discharging processes can be shown as: