Ask A Scientist Chemistry Archive

 
name         Rita M.
status       student
age          50s

Question -   Is it possible for the density of an alloy containing
gold to ever equal the same density of pure gold?
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Rita,

The only way that the alloy could have the same density as that of pure gold (19.3 grams per cubic 
centimeter) is if the alloying metal had the same density as that of gold AND the alloying atoms 
packed (fit) in the solid crystal lattice in the same way as gold atoms. Since those elements 
(metals) that are known to alloy with gold all have densities and atomic sizes different from 
that of gold, I think the answer to your question is, "no."

Regards,
ProfHoff 870
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It would certainly be possible if you used an alloy with three metals.
Gold, a metal lighter than gold and a metal heavier than gold.  The
latter two would have to be in a ratio so their combined density was
equal to gold.

Greg Bradburn
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Sure.   Some "other metals" are heavier, some lighter, than gold.
Alloys with equivalent amounts of heavier and lighter additives will have the same density as gold.
However, the few elements heavier than gold are either more expensive than gold (Pt, Ir, Os)
or do not alloy too well, and make it look a little poor (Re, W).
So measuring density has some value in detecting "economic cheating".

Measuring density and one other property (conductivity, reflectivity, annealing behavior) has more such value.
Suppose someone adds Tungsten (W) to make it heavier, and copper / silver/ nickel to make it lighter,
ending with an alloy of density equal to gold.   This alloy must be harder and less conductive than pure gold.
And it would discolor when heated in air.

Jim Swenson
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