How to distinguish if gold is real gold?

Question

This guy gives you this chunk of gold. Says its pure gold. Do you believe him? How can you set up an experiment so the whole thing is gold? anything to do with its density, resistance, anything you can think of :) thanx.

Answer 1

If you have no acid lying around, or a mass spectrometer,, you can still do Archimedes' density test.  Works best with lab equipment, but you can get by with just a graduated cylinder, because you need to accurately measure a quantity of water.  And of course, you need an accurate scale.

The method consists of measuring the gold's weight on the scale, and then measuring it's volume. Put a pitcher in a sink and fill it with water until it is overflowing.   Hold your graduated cylinder under the spout of the pitcher, and put the gold in the pitcher, catching all the overflow.  When you know how much it weighs, and how much volume it has, sit down with a calculator.  24K gold has a density of 19.3 grams / cubic centimeter.  If your lump of metal does not have that density (within your measuring limits), it's not gold.

Of course it could be that density and still be a trick.   That's where the acids and mass spectrometers come in.

Gold is a ridiculously good electical conductor, but silver and copper are pretty good, too, so there are no well known conductivity tests.

Wave a magnet at it for fun.  Real gold is neither attracted nor repelled by a magnet, so if it moves, it's not gold.

Gold is very ductile, and can be hammered into very thin sheets.  I don't know what the seller would think if you wanted to pound his lump of gold flat.

By the way, how well do you know the seller?  And where did he say he got the gold?

Answer 2

Dunk it in a tumbler of diluted nitric acid or hydrochrolic acid. It should not lose even a gram of weight after 10 minutes.

Answer 3

Try to make a mercury amalgam. See if everything dissolves. Evaporate the mercury. And measure the density. Make sure there are no air pockets. Gold is also a soft metal so malleability, it should be easy to make marks in and you can roll it out into thin strips. A 100% piece of gold should be soft. Melting point/boiling point. Gold is also non magnetic. Try to disolve it in conc. HCl or nitric acid. Since neither will disolve gold. However if the impurities are sealed in the gold or insoluble in the acids that might not be useful. Also the impurities might end up combining to be the same density as the gold anyway. You would have to perform a series of tests. Or you could stick the whole sample though a mass spec maybe. You would probably have to go through the process of purifying the gold first and then test it.