Chemical Effects
المؤلف:
GEORGE A. HOADLEY
المصدر:
ESSENTIALS OF PHYSICS
الجزء والصفحة:
P-373
2025-12-10
40
Demonstrations. - Fit corks to the two sides of a U-tube. Through these corks pass copper wires with platinum terminals. Fill the tube nearly to the top of the terminals with a solution of sodium sulphate (Na2SO4) colored with blue litmus. Couple two or three cells in series to the copper wires, and in a few minutes the solution in the U-tube near the + terminal will turn red, showing the presence of an acid, while the color at the - terminal shows the presence of an alkali .
Rinse the U-tube used in the above experiment, and fill it nearly full of water to which a few drops of sulphuric acid have been added. Cut a notch along the side of each cork and couple three dry cells in series. Bubbles of gas will be noticed at each terminal. Those given off at the + terminal are oxygen and those at the - terminal are hydrogen.
The relative quantities of the gases given off at the terminals can be measured by using a form of apparatus like that shown in Fig. 2. This is known as Hoffman's apparatus, and with it the hydrogen collected over the negative terminal is shown to be twice the volume of the oxygen collected over the positive terminal.
The action of the current shown in these demonstrations is called electrolysis, and the solution in which this action goes on is an electrolyte. The apparatus used in electrolysis is called a voltameter; and the terminals, electrodes. The electrode by which the current enters the electrolyte is called the anode, and that by which it leaves, the cathode. The parts into which the current separates the electrolyte are called ions; that which goes to the cathode is called the cation; and that which goes to the anode is called the anion. From the direction which the ions take in the electrolyte their electric condition is determined; hence the cation is considered electropositive and the anion electronegative.
In the experiment with sodium sulphate the Na2SO4, on going into solution, breaks up into positively charged ions, +Na, and negatively charged ions, - SO4. When the SO4 ions, sulphions, reach the positive platinum plate, as they will by mutual attraction, they give up their negative charge and attack the water, forming H₂SO4, and setting O free. The Na ions give up their positive charge to the negative plate, attack the water, and form NaOH, setting H free.
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