Short Question Answers on Direct current
1. Distinguish between conduction of electricity through a metallic wire and an electrolyte?Ans Metallic conduction differs from electrolytic conduction due to following reasons:
(a) The conduction of electricity in metals is due to the drifting of free electrons, while the conduction of electricity is electrolyte is due to the movement of positive and negative ions.
(b) No chemical changes take place when current is passed through metal but chemical decomposition of the electrolyte occurs when current is passed through it.
(c) No matter is transformed during electric conduction metals but matter is trnasported in the form of positive and negative ions in case of electrolytes.
2. Explain why the anode of copper voltameter is made of copper?
Ans When current is passed through CuSO4 solution in a copper voltameter, copper ions move towards cathode (being positively charged) while sulphate ions towards anode (being-very charged). Copper ions transfer their charge to cathode and become copper atoms. The sulphate ions on the anode interact with copper atoms and form CuSO4. The cathode gain as much weight as the anode loses. This makes necessary for the anode in a copper voltameter to be made for copper.
3. Expalin how you can use a voltameter for measuring current.
Ans Suppose that on passing current through a voltameter for known time t, the increase in mass of the cathode is m. Then according to Faraday's first law
m = Z I t
where z is ECE of the substance. It follows that
i.e. knowing m, t and z, the current passed through the voltmeter can be determined.<
4. Pure water and dry salt are both non-conductorof electricity but the solution of salt in water is a conductor of electricity. Expalin why?
Ans There are no free ions to carry the electricity in pure water or dry salt but when dry salt is dissolved in water, ionization takes place. Salt ionizes inot Na+ and Cl- ions which carry electricity and solution becomes conducting.
5. What is the difference between electrochemical equivalent and chemical equivalent?
Ans Electrochemical equivalent of a substance may be defined as the mass of ions liberated, when one coulomb of charge passes through the electrolyte.
On the other hand, chemical equivalent = atomic weight/valency 6. What do you understand by Faraday? What is its value?
Ans The quantity of charge required to deposit one gram equivalent (i.e. one chemical equivalent expressed in grams) of any substance, is known as Faraday. Its value is 96500C mol−
7. A simple voltaic cell has an emf equal to 1.0V. When the circuit is open, is there a net field, which would give rise to a force on a test charge (i) inside the electrolyte of cell (ii) outside the cell?
Ans (i) There are two electric fields inside the cell, one is the electrostatic field due to emf of the cell while another field is of non-electrostatic origin (due to chemical reactions taking place inside the cell). (ii) Outside the cell, the net field is the electrostatic field between the two plates of the cell (due to charges on the plates).
8. When a secondary cell of emf. 2.0 V is being charged by an external supply, is the terminal voltage of the secondary cell greater or less than 2.0 V?
Ans When a secondary cell is being charged, current inside the cell flows in the direction of electrostatic field (i.e., from positive plate ot the negative plate). Now the electrostatic field is greater than the non electrostatic field, and therefore, the terminal voltage (which is determined by electrostatic field) is always greater than the emf. (which is determined by non-electrostatic field).
9. The capacity of a storage cell is marked as 3.5 A at 1h discharge rate. What does this signify? Can the cell provide 16 A for 15 minutes?
Ans The storage cell can supply 3.5 amp current continuously for 1 hour or 0.35 amp current for 10 hours. Now maximum current that can be drawn continuously for 15 minutes = 3.5 × 4 = 14.0 amp. As 16 amp >14 amp, hence cell can not supply 16 amp current for 15 minutes.
10. You are given a primary and a secondary cell of the same emf. From which cell you will be able to draw larger current and why?
Ans Since the internal resistance of a resistance of a secondary cell is very small, hence a larger current can be drawn from this cell as compared to that from a primary cell.
11. Do electrons carry current inside an electrolytic cell?
Ans No, the current carries inside an electrolytic cell are the positive and negative ions.
12. Name the current carries in the external circuit of an electrolytic cell?
AnsThe current carriers are the electrons.
13. Is the current in the external circuit more or less than the total current inside the cell?
Ans From continuity of current, the current in the external circuit is equal to the toal current of the positive and negative ions inside the cell.
14. Why does voltameter measure current more accurately than an ammeter?
Ans A voltameter measures current in terms of mass of ions (m) deposited and electrochemical equivalent (Z) of the substance (i.e. I = m/Zt). Since values of m and z are measured to 3rd decimal place and 5th decimal place respectively. The time (t) of passage of current is also measured accurately. The relative error in the measured of current by voltameter will be very small as compared to that when measured by ammeter directly. Hence voltameter measures current more accurately than an ammeter.
15. What is the function of charcoal and manganese dioxide used in the porous pot of Leclanche cell?
Ans Charcol and manganese dioxide are used in porous pot of leclanche cell as oxidizer. Manganese dioxide removes polarization effect. It oxidises layer of hydrogen ions and removes the back emf.
16. What is meant by Faraday's Constant?
Ans Faraday constant (F) is the amount of charge which will liberate or deposit one gram equivalent (or chemical equivalent in grams) of a substance during electrolysis. It may also be defined as the amount of chrge required to liberate or deposit one mole of monovalent substance is electrolysis. Its value is approximately 96500 coul mol-1.
No comments:
Post a Comment