Discussing how percentages are used in the chemical industry

Click on a question and look for the answer here.

Do chemists always use chemicals that are 100% pure?

No! In practice total purity cannot ever be achieved.  Substances are graded according to their percentage purity and this information is provided by suppliers. For example, a catalogue from a chemical supplier quotes the following prices for copper sulfate:

technical grade is £9.28 for 1 kg, 
 98+%  is £15.86 for 1 kg,  
 99.5+% is £35.36 for 1 kg.

Chemists must try to get the correct balance between percentage purity and cost.

Do naturally occurring ores, always contain the same percentage of useful minerals?

No, the composition of the actual ore varies from place to place. For example, the impurities in an aluminium ore are iron(III) oxide (3-25%), silica (1-7%) and titanium dioxide (2-3%). When new deposits are formed, they are sampled, tested and the percentages are worked out.

Why are chemists interested in the percentage yield?

The percentage yield is calculated from the formula

% yield = actual yield x 100

                 Theoretical yield

It is important because it tells us the efficiency of the process, ie, how close we are to the theoretical yield. During chemical production some of the product is usually lost during the process. For example during processes such as filtering or pouring.

Are percentages important in other areas of the industry? 

Yes, they play an important role in marketing and sales. The industry needs to know the market so that they don’t over or under produce a product. Using percentages can simplify some of the calculations.

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