Project Idea

How chemical energy may be changed into electrical energy.; The electrical energy which caused the ringing of the bell was generated in a battery cell by a chemical action.; The simplest form of a cell of this kind, called the voltaic cell, was invented in 1800 by Alessandro Volta, a professor in an Italian University.; You can easily make a cell of this kind.

Energy Science Experiment

In a jar containing dilute sulphuric acid place two metal plates; one of zinc and the other of copper.; If each plate (called an electrode) is connected by means of a wire with the binding posts of an electric bell, the bell will ring.; After a few minutes the bell ceases to ring although the circuit has not been broken.;

An examination of the copper plate will show that it is covered with bubbles of a gas, so that the acid is not able to touch it.; The battery is now said to be polarized.; If the bubbles are rubbed off, the bell will again begin to ring.; Various methods have been used to prevent this polarization.; One method is illustrated by the gravity cells.; In this cell, the copper is placed at the bottom of the jar in a solution of copper sulphate, (blue vitriol); and the zinc near the top in weak sulphuric acid.; The blue vitriol solution is heavier than the acid, and remains at the bottom; hence the name gravity cell.;

The blue vitrio1 or copper sulphate solution prevents the gas (hydrogen) ;from reaching the copper plate, but it causes copper to separate from the solution and be deposited on the copper plate as a bright layer.;

In the Daniell cell, the zinc and sulphuric acid are in a porous cup which is placed in a jar containing the copper and blue vitriol solution.; In another form of cell, one electrode is carbon and the other zinc, and the liquid in which they are immersed is a strong solution of sal ammoniac (ammonium chloride).;

The dry cell, which for most purposes is more convenient than any other, is like the last cell mentioned, except that, instead of a jar, a cup or cylinder made of zinc is used as the container, and this forms one electrode.; Then instead of sal ammoniac solution being used, a moist paste saturated with sal ammoniac and usually containing manganese dioxide to prevent polarization, is packed between the carbon and this zinc outer wall.