Q25 of 30 Page 1

(a) What is thermite process? Where is this process used? Write balanced chemical equation for the reaction involved.

(b) Where does the metal aluminium, used in the process, occurs in the reactivity series of metals?


(c) Name the substances that are getting oxidised and reduced in the process.


The thermite process involves the reaction of metal oxides with Aluminium.

When highly reactive metals such as sodium (Na), calcium (Ca) aluminium (Al) are used as reducing agents, they have the tendency to displace the metals of lower reactivity from the compound. These displacement reactions are highly exothermic. The amount of heat evolved is so large that metals produced in this reaction would be in a molten state.


Balanced Chemical Reaction:


2 Al(s) + Fe 2O 3(s) → 2Fe (s) + Al 2O 3 (s)


Applications of thermite process:


(1) The reaction of Iron Oxide (Fe2O3) with aluminium is used to join railings of railway tracks or to join cracked machine parts.


(2) It is also used for joining the cracked metal utensils in the households.


(b) In the reactivity order of metals, Aluminium occurs above the Hydrogen.


(c) Aluminium is getting oxidised whereas Iron is getting reduced in this process.


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23

(a) State the relation correlating the electric current flowing in a conductor and the voltage applied across it. Also draw a graph to show this relationship.

(b) Find the resistance of a conductor if the electric current flowing through it is 0.35 A when the potential difference across it is 1.4V


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(a) Write the mathematical expression for Joule's law of heating.

(b) Compute the heat generated while transferring 96000 coulomb of charge in two hours through a potential difference of 40 V.


 26

The position of certain elements in the Modern Periodic Table are shown below.

Using the above table answer following questions giving reasons in each case:


(i) Which element will form only covalent compounds?


(ii) Which element is a non-metal with valency 2?


(iii) Which element is a metal with valency 2?


(iv) Out of H, C and F which has largest atomic size?


(v) To which family does H, C and F belong?


OR


Define atomic size. Give its unit of measurement. In the modern periodic table what trend is observed in the atomic radius in a group and a period and why is it so?


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(a) Why is there a difference in the rate of breathing between aquatic organisms and terrestrial organisms? Explain.

(b) Draw a diagram of human respiratory system and label – pharynx, trachea, lungs, diaphragm and alveolar sac on it.


OR


(a) Name the organs that form the excretory system in human beings.


(b) Describe in brief how urine is produced in human body.