SPRK-12-BMT–5-CHEMISTRY-SURFACE CHEMISTRY 5 Time: 1 hr. XII-CHEMISTRY SURFACE CHEMISTRY Maximum Marks: 30 INSTRUCTIONS: 1. All the questions are compulsory. 2. Questions no. 1-6 are very short answer question and carry 1 mark each. 3. Question no. 7-10 are short answer question and carry 2 marks each 4. Question no. 11-12 are also short answer questions and carry 3 marks each. 5. Question no. 13-14 are long answer question and carry 5 marks each. 6. Use long tables if necessary, use of calculators is not allowed. 1. Of physisorption or chemisorptions, which has a higher enthalpy of adsorption? 2. What is especially observed when a beam of light is passed through a colloidal solution? 3. How is a sol different from an emulsions? 4. Write two applications of adsorption. 5. Why do true solutions not show Tyndall effect? 6. How can a colloidal solution and true solution of the same colour be distinguished from each other? 7. What are lyophilic and lyophobic colloides? Which of these sols can be easily coagulated on the addition of small amounts of electrolytes? 8. 9. Write the differences between physisorption and chemisorptions with respect to the following i) Specificity ii) Temperature dependence iii) Reversibility and iv) Enthalpy change What is meant by coagulation of a colloidal solution? Describe briefly any three methods by which coagulation of lyophobic sols can be carried out. 10. Describe a conspicuous change observed when: i) a solution of NaCl is added to a sol of hydrated ferric oxide. ii) a beam of light is passed through a solution of NaCl and then through a sol. 11. What are the characteristics of the following colloids? Give one example of each. i) Multimolecular colloids iii) Emulsions ii) Peptization 12. SPRK-12-BMT–5-CHEMISTRY-SURFACE CHEMISTRY How are the types of emulsions different from one another? Give suitable example to justify the difference. State two applications of emulsions. 13. a) Adsorption of a gas on surface of solid is generally accompanied by a decrease in entropy, still it is a spontaneous process. Explain. b) Some substances can act both as colloids and crystalloids. Explain. c) What will be the charge on AgI colloidal particles when it is prepared by adding small amount of AgNO3 solution to KI solution in water? What is responsible for development of this charge? 14. a) Why is finely divided substance more effective as an adsorbent? b) Explain what is observed when i) an electric current is passed through a sol ii) a beam of light is passed through a sol iii) an electrolyte (say NaCl) is added to ferric hydroxide sol c) Define ‘electrophoresis’. *****END OF TEST PAPER*****