Category: Basic Chemistry K-Scheme Lab Manual Answer

 Practical No. 05: Determination of Electrode Potential of Iron

• Conclusion: Zinc is more electropositive than iron (-0.76 V vs -0.44 V). Therefore zinc acts as sacrificial anode protecting iron from corrosion.
• Recommendation: Use clean electrodes and fresh electrolyte solutions for accurate measurements.

• Answer: De-electronation is the process of removal of electrons from an atom or ion, i.e., oxidation (loss of electrons). Electronation is the process of addition of electrons to an atom or ion, i.e., reduction (gain of electrons). At anode, de-electronation occurs, and at cathode, electronation occurs in an electrochemical cell.

• Answer: Factors influencing electrode potential of iron include:
  • (i) Nature of the metal and its ions.
  • (ii) Concentration of metal ions in solution.
  • (iii) Temperature of the solution.
  • (iv) Pressure (for gaseous electrodes).
  • (v) Nature of the electrolyte.
  • (vi) Surface condition of the electrode.

• Answer: Applications include:
  • (i) Designing corrosion protection systems like sacrificial anodes and cathodic protection.
  • (ii) Electroplating and galvanization of iron surfaces.
  • (iii) Manufacturing of batteries and electrochemical cells.
  • (iv) Determining the feasibility of redox reactions.
  • (v) Metallurgy and metal extraction processes.
  • (vi) Sensor and analytical applications.

 Practical No. 04: Determination of Electrode Potential of Copper

• Conclusion: Zinc is more electropositive than copper (lower reduction potential -0.76 V vs +0.34 V). Hence zinc undergoes corrosion in preference to copper when in contact.
• Recommendation: Clean electrode surfaces, use fresh solutions, and ensure proper connections for accurate readings.

• Answer:
  • At Anode (Zinc electrode – oxidation): Zn → Zn²⁺ + 2e⁻ (Zinc loses electrons and dissolves as Zn²⁺ ions).
  • At Cathode (Copper electrode – reduction): Cu²⁺ + 2e⁻ → Cu (Copper ions gain electrons and deposit as copper metal on the electrode).
  • Net Reaction: Zn + Cu²⁺ → Zn²⁺ + Cu.

• Answer: Lower reduction potential indicates a higher tendency to undergo oxidation (corrosion). Metals with more negative reduction potentials (like Zn, Fe) have a higher tendency to lose electrons and corrode. Metals with positive reduction potentials (like Cu, Ag) have a lower tendency to corrode. Thus, more electropositive metals corrode preferentially.

• Answer: Zinc electrode acts as the Anode (negative terminal) where oxidation occurs. Copper electrode acts as the Cathode (positive terminal) where reduction occurs. Electrons flow from zinc (anode) through the external circuit to copper (cathode), and conventional current flows from copper to zinc.

 Practical No. 03: Identification of States of Matter

• Conclusion: Matter exists in solid, liquid, and gas states depending on temperature and pressure.
• Recommendation: Use simulation carefully, record observations systematically, and plot accurate graphs for precise determination of phase transition temperatures.

• Answer: Particles of matter have the following characteristics:
  • (i) They are continuously moving.
  • (ii) They have spaces between them.
  • (iii) They attract each other (intermolecular forces).
  • (iv) They are very small in size.
  • (v) The kinetic energy of particles increases with an increase in temperature.
  • (vi) The movement of particles decreases with a decrease in temperature.

• Answer: The physical state of a substance is determined by:
  • (i) Temperature: Increasing temperature changes solid to liquid and liquid to gas.
  • (ii) Pressure: Increasing pressure can change gas to liquid and liquid to solid.
  • (iii) Intermolecular forces: Stronger forces favour the solid state, while weaker forces favour the gaseous state.
  • (iv) Kinetic energy of particles: Higher kinetic energy favours the gaseous state.

• Answer:
  • At 0°C: Water exists in two states — solid (ice) and liquid (water) at the melting point (both coexist).
  • At 100°C: Water exists in two states — liquid (water) and gas (steam/water vapour) at the boiling point (both coexist).
  • Note: Above 0°C and below 100°C, water is purely in a liquid state.

 Practical No. 02: Identification of Anions

• Conclusion: Systematic anion analysis with group reagents effectively identifies acidic radicals.
• Recommendation: Use freshly prepared reagents, avoid contamination, and perform tests in proper sequence for accurate results.

• Answer: The acidic radical is CO₃²⁻ (Carbonate). When carbonate reacts with dilute HNO₃, it liberates CO₂ gas which turns lime water milky due to formation of CaCO₃. The effervescence observed confirms the presence of carbonate ion.

• Answer: To separate halides, add dilute HNO₃ followed by AgNO₃ solution. White precipitate indicates Cl⁻, pale yellow precipitate indicates Br⁻, and yellow precipitate indicates I⁻.
• Confirmation: For further confirmation, add chloroform and chlorine water — chlorine water liberates halogens which dissolve in chloroform giving characteristic colours: Cl⁻ gives colourless layer, Br⁻ gives yellowish brown layer, and I⁻ gives violet layer.

• Answer: The anion is SO₄²⁻ (Sulphate). Barium nitrate gives a white precipitate of BaSO₄ which is insoluble in dilute HNO₃. This confirms the presence of sulphate ion. The confirmatory test can also be performed using BaCl₂ solution which gives the same white precipitate.