CBSE Class 12 Chemistry General Principles and Processes of Isolation of Elements (1). CBSE issues sample papers every year for students for class 12 board exams. Students should solve the CBSE issued sample papers to understand the pattern of the question paper which will come in class 12 board exams this year. The sample papers have been provided with marking scheme. It’s always recommended to practice as many CBSE sample papers as possible before the board examinations. Sample papers should be always practiced in examination condition at home or school and the student should show the answers to teachers for checking or compare with the answers provided. Students can download the sample papers in pdf format free and score better marks in examinations. Refer to other links too for latest sample papers.
One mark Questions
1.Differentiate between a mineral and an ore.
Ans: the naturally occurring chemical substances present in the earth’s crust which can be obtained by mining are called minerals while minerals from which metals can be extracted economically are called ores.
2. Why is it that only sulphide ores are concentrated by froth floatation process.
Ans: This is because sulphide ores particles are wetted by oil and gangue particles are wetted by water.
3. Name one acidic flux and one basic flux.
Ans: silica and lime
4. Name the chief ore of silver.
Ans: argentite or silver glance
5. Name a reagent used during leaching of bauxite ore.
Ans : NaOH (sodium hydroxide)
6. Why is silica added to sulphide ore of copper in the reverberatory furnace?
Ans : in order to remove the iron impurity as slag
7. What is the role of flux in metallurgical processes?
Ans : flux is used for making the molten mass more conducting.
8. What is the thermodynamic relation between Gibbs free energy and emf of the cell.
Ans: ΔG0= —nFE0
9. What is the relation between gibbs free energy and equilibrium constant?
Ans: ΔG0= —RTlnK
10. Give the expression for Gibbs Helmholtz equation.
Ans : ΔG= ΔH—TΔS
11. Name one chemical which can be used to concentrate galena selectively by froth floatation process.
Ans: sodium cyanide (NaCN)
12. What type of ores are roasted?
Ans : sulphide ores
13. Out of C and CO which is a better reducing agent for ZnO?
Ans : the free energy of formation of CO from C becomes lower at temp. above 1120K whereas that of CO2 from C becomes lower above 1323K than free energy of formation of ZnO. The free energy of formation of from CO is always higher than that of ZnO. Therefore, C can reduce ZnO to Zn better than CO. CO2 from CO is always higher than that of ZnO. Therefore, C can reduce ZnO to Zn better than CO.
14. What is the chemical principle on which chromatography separation based on?
Ans : Adsorption
15. What are the products obtained during the electrolysis of brine solution? Also write the name of this process.
Ans : chlorine, hydrogen and sodium hydroxide. The process is popularly known as chlor-alkali process.
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