Avagadro Number Essay

933 Words4 Pages
EXPERIMENTAL DETERMINATION OF AVAGADRO NUMBER Purpose The objective is to make an experimental measurement of Avogadro's number. Introduction A mole can be defined as the gram formula mass of a substance or the atomic mass of an element in grams. In this experiment, electron flow (amperage or current) and time are measured in order to obtain the number of electrons passing through the electrochemical cell. The number of atoms in a weighed sample is related to electron flow to calculate Avogadro's number. In this electrolytic cell both electrodes are copper and the electrolyte is 0.5 M H2SO4. During electrolysis, the copper electrode (anode) connected to the positive pin of the power supply loses mass as the copper atoms are converted to copper ions. The loss of mass may be visible as pitting of the surface of the metal electrode. Also, the copper ions pass into the water solution and tint it blue. At the other electrode (cathode), hydrogen gas is liberated at the surface through the reduction of hydrogen ions in the aqueous sulfuric acid solution. The reaction is: 2 H+(aq) + 2 electrons -> H2(g) This experiment is based on the mass loss of the copper anode, but it is also possible to collect the hydrogen gas that is evolved and use it to calculate Avogadro's number. Materials * Direct current source (battery or power supply) * Insulated wires and possibly alligator clips to connect the cells * 2 Electrodes (e.g., strips of copper, nickel, zinc, or iron) * 250-ml beaker of 0.5 M H2SO4 (sulfuric acid) * Water * Alcohol (e.g., methanol or isopropyl alcohol) * Small beaker of 6 M HNO3 (nitric acid) * Ammeter or multimeter * Stopwatch * Analytical balance capable of measuring to nearest 0.0001 gram Procedure Obtain two copper electrodes. Clean the electrode to be used as the anode by immersing it in 6 M HNO3 in a fume
Open Document