Why purity is in 99.99 percent?

Answer 1

Come on... That is a fraction for - as close to 100% your are going to get for some things. Gold for instance.

**************** This is partly true, for substances such as gold which are sold at retail for ordinary use, such as jewelry. 99.99% pure gold is in fact purer than is usually needed for most end uses of gold...but not all.

Some chemicals, metals, and materials, especially those used in industry and within preparative or research laboratories, must be considerably purer than 99.99% pure. For example, the silicon, germanium, gallium, arsenic, phosphorus, indium, hafnium, and several other materials used to make integrated circuits must be greater than 99.9999% purity! Otherwise, very small circuit elements simply won't work -- the very small contaminations could change a calculation and create unacceptable errors and equipment failures.


Even gold, when required for researches in solid state physics and advanced materials chemistry, must be -- and can be -- purified well beyond 99.99% purity. But here, the usage is not retail -- it is for strictly laboratory or industrial purposes.