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ELECTRICAL MEASURING INSTRUMENTS For the detection or measurement of electric current, potential difference, and resistance certain instruments have been devised viz. The galvanometer for the detection of small currents measurements of small currents of the order of micro amperes or mili amperes the voltmeter or potentiometer for the measurement of potential difference (and voltage) between two points of a circuit are the EMF of a source the ammeter for the measurement of large currents the wheatstone bridge the meter Bridge the post office box and the ohmmeter for the measurement of resistance. THE MOVING COIL GALVANOMETER The moving coil galvanometer is a basic electrical instrument it is used for the detection (and Measurement) of small currents. Its underlying principle is the fact that when a current flows in a rectangular coil placed in a magnetic field it experiences a magnetic torque. If it is free to rotate under a controlling torque, it rotates through an angle proportional t...
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HOW TO PREPARE POTASH ALUM?

OBJECT :

To prepare potash alum (K2SO4,Al2(SO4)3.24H2O)

APPARATUS :

China dish,beaker,watch glass,funnel,conical flask,glass rod,filter paper,water trough,wire gauze,tripod stand and bunsen burner.

CHEMICALS :

Solid Aluminium sulphate [Al2(SO4)3.16H2O](7.7 gms) , K2SO4 (2.0 gms), 50 mls of distilled water,few drops of conc H2SO4

EQUATIONS :

K2SO4 +Al2 (SO4)3.16H2O + 8H2O --------------> K2SO4.Al2(SO4)3.24H2O

THEORY :

The term alum was originally used for potassium aluminium sulphate [K2SO4.Al2(SO4)3.24H2O] commonly known as potash alum.The term alum is now used for all double sulphates having general formula R2SO4.M2(SO4)3.24H2O

PROCEDURE :

Weigh out 7.7 gm of aluminium sulphate and dissolve it in about 30 mls of boiling distilled water.Add few drops of H2SO4 (conc) to make the solution clear.In another beaker dissolve 2.0 g of K2SO4 in 20 mls of distilled water.Mix the two solutions and concentrate the solution to crystallization by heating it in a china dish.Now cool this concentrated solution in ice cold water.After few minutes, crystals of alum separates out.

RESULT :

Colorless crystals of potash alum are obtained.

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