Plumbers solder is an alloy of the elements lead and tin. Can this alloy be both substitutional and interstitial? How do you know?  

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An alloy is a mixture of different metals prepared by mixing the metals in their molten (liquid) state and then allowing them to cool.

There are three types of alloys.

  • Homogeneous: Homogeneous alloys have the same crystal structure as one of the original metals.  There are two types of homogeneous alloys, substitutional and interstitialSubstitutional alloys are formed from metals with similar atomic radii. Because of this, one metal atom can replace other metal atom in the crystal lattice. Substitutional alloys retain similar properties to those of the original metals. Interstitial alloys have different sized atomic radii. The metal with the smaller atomic radius is able to insert itself in between the atoms of the other metal. Interstitial alloys are more rigid and less malleable than the original metals.
  • Intermetallic: Intermetallic alloys have crystal structures that are different from the crystal structures of the original metals. Intermetallic alloys often have properties that are different than the original metals.
  • Heterogeneous: Heterogeneous alloys have multiple crystal structures and phases throughout the alloy. The properties of heterogeneous alloys vary a great deal.

Plumbers solder is an alloy composed of tin (Sn) and lead (Pb). it is an example of a heterogeneous alloy because it is not composed of a regular crystal structure. It is not an interstitial or substitutional alloy, as these are categories of homogeneous alloys. 

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