Project:“I experiment and… I find my way” Scientific workshop for teachers and students of Primary School and Junior High School

Teachers in charge of the project: Cinzia Lattanzi, Gigliola TrapassoIPIA E.Rosa Sarnano

School year: 2009/2010

presents

classes 3A/3B Comprehensive School in San Ginesio (MC)

in “Electron flow and Daniell’s Battery”

Educational activities

Electron flow and Daniell’s Battery

Aim: to demontrate the production of current from chemical reactions.

Meterials • Voltmeter;• Solution of copper sulphate

(CuSO4) 1 M;• Zinc sulphate (ZnSO4) 1 M;• 2 beckers;• Zinc foil;• Copper foil;• Solution of sodium sulphate

(Na2SO4) for the saline bridge;• Electric cables;• Filter paper

Procedure

• Part 1: Electron flow observation

• Immerse the zinc foil into the solution of CuSO4: observe the deposit of copper on the zinc foil; the solution of CuSO4 (light blue) loses its colour with the passing of time. This shows that the ions Cu++ deposit onto the foil as Cu (at the same time, the Zn foil loses its mass because in the solution Zn turns into Zn++).

• Part 2: Production of electric current

• Put the two chemical species (oxidiser and reducer) into the two different beckers and connect them with a conductor;

• Becker no. 1 (solution of ZnSO4: Zn++ and SO4--) with a zinc foil (semi-element Zn++/Zn);

• Becker no.2 (solution of CuSO4: Cu++ and SO4--) with a copper foil (semi-element Cu++/Cu) ;

• Saline bridge: strip of paper soaked in Na2SO4, sodium sulphate (solution with ions Na+ and SO4--);

• Using a wire, connect the two foils with the voltmeter or a bulb.

Comment and drawing• The Voltmeter shows the presence of current (ca. 1.1 volt);• The Cu foil thickens (Cu++ + 2 e Cu);• The Zn foil becomes thinner (Zn Zn++ + 2 e).• The blue solution of CuSO4 becomes lighter as time passes (the blue

colour is given by the ions Cu++).

anode cathode

Voltmeter

Saline bridge

Expaination of the phenomena• Zinc releases 2e- onto the foil and, through the solution, it turns into Zn++.

The foil charges negatively and works as an ANODE (negative pole). Thanks to the conductor, the electrons freed by the zinc on the electrode, pass to the copper electrode and are captured by the ions Cu++. The electrons captured turn Cu++ into metallic copper (Cu), which deposits onto the electrode. The copper foil works as a CATHODE (positive pole).

• Thus, by means of a spontaneous reaction of oxidation-reduction, chemical energy is transformed into electricity.

The saline bridge: When the battery works, the anode area gains ions Zn2+, whereas the cathode area loses ions Cu2+. The excess of positive charges in the solution prevents the anode from further transformations of atoms of zinc into ions Zn2+. In the anode, the lack of positive charges prevents a further transformation of ions Cu2+ into Cu.With its ions, the saline bridge - a pipe made of glass or blotting paper filled with a solution of sodium sulphate (Na2SO4) - neutralizes the charges which are gathering in the two half-cells. The anions SO4– will move towards the anode to balance the positive charge which is here produced, whilst the ions Na+ will move towards the cathode to balance the surplus of negative ions which are gathering. Moreover, the saline bridge aims at connecting the two solutions, i.e. to ‘close’ the circuit.

Thank you for your attention.

IPIA E. Rosa Sarnano MC

Chemical-Biological course