The Size of an Atom
The size of an atom is too small to imagine. Counting the number of atoms in even a microscopic amount of material is an impossible task – it would take a billions years. It turns out, however, that is it possible to apply a thin surface coating of metal atoms onto another metal. This is done to change the properties of the underlying or base metal. In this experiment, the thickness of a zinc metal coating on galvanized iron will be determined and use to “count” the number of layers of atoms in the coating.
• Atomic Size • Density, mass, and volume
Galvanized iron is produced by coating iron with a thin layer of metallic zinc. The zinc coating protects the underlying iron metal against rusting or corrosion. Zinc is more reactive than iron and thus reacts with oxygen in the air and with water before the iron does. In this ay, the zinc coating prevents oxygen from reaching the iron. The greater the reactivity of zinc continues to protect the iron even after the surface of the zinc has been broken or breaches. Galvanized iron has many applications, including rain gutters, heating ducts, nails, and screws.
The amount of zinc deposited on the surface of galvanized iron can be determined by reacting the zinc with hydrochloric acid, according to the following reaction:
Zn(s) + 2HCl(aq) ® ZnCl2(aq) + H2(g) Equation 1
The products of the reaction are zinc chloride, which dissolves in the hydrochloric acid solution, and hydrogen gas, which bubbles out of the solution. By measuring the mass of a piece of galvanized iron before and after its reaction with hydrochloric acid, the mass of zinc that reacted can be calculated. The mass of zinc can be related, in turn, to the number of layers of zinc atoms in the zinc coating by considering the density of the metal, the surface area of the galvanized irons, and the size of a zinc atom.
The purpose of this experiment is to determine the number of layers of zinc atoms in the protective coating on a sheet of galvanized iron.
Electronic Balance Forceps
Beakers, 250 mL and 400 mL Galvanized iron metal
Hydrochloric acid, HCl, 6 M, 50 mL Metric ruler
Paper towel Tap Water
Hydrochloric acid solution is toxic by ingestion or inhalation and is severely corrosive to skin and eyes. Avoid contact with skin and eyes. The pieces of galvanized iron may have sharp edges that can cut skin. Handle the metal pieces with forceps. Wear chemical splash goggles. Wash hands thoroughly with soap and water before leaving the laboratory.
(Determine the volume of the galvanized iron by using a water displacement method.)
Post-Lab Calculations and Analysis
Number of layers of zinc atoms = Thickness of zinc coating per side (cm)
Diameter of zinc atom (cm)