According to the regulations, any chemical products released into the state or private enterprises, must have a quality certificate, which States the percentage content of the basic substance and the most significant impurities. This is determined by the laboratory using the methods of qualitative and quantitative analysis. The certificate attached to any particular batch of products, and its key indicators should be shown on each packing unit.
For example, the well-known salt is sodium chloride. Buying a pack of the brand "Extra" mass of 1 kilogram how much pure salt you buy? Look at the information on the package. If the content of the basic substance of 99.7%, which is very good, which is not surprising, because "extra" means a high degree of purification. Therefore, the pure substances in the packing unit contains: 1000*0,997=997 grams. The other three grams are distributed between different impurities. Of course, other, less purified grades of salt, a content of pure substance will be lower.
Or here's a task that will certainly appeal to the fair sex. Suppose you have a gold ring 585-th test, weight 20 grams. How much pure gold it contains? To give an answer to this question is very simple, you only need to remember what is the meaning of "test". In Russia, its value indicates what percentage of pure precious metal in 1000 weight fraction of the product. Therefore, a 585-I test corresponds to a concentration equal to 58,5%. Perform the calculation in one step: 20*0,585=11.7 grams. That is how much pure gold is contained in the ring.
And what about, for example, if the ring is the work of the English masters, and weighs 20 grams, but the stigma is the sample specified something strange- "18K"? How, then, to find the amount of pure gold in the product? And then there is absolutely nothing complicated. The fact that the UK adopted the "K" scale of purity of precious metals. Higher theoretically, 100% concentration corresponds to 24 carats. Then the product would be marked with "24K". There is a stamp "18K", this means that the product weight 18 parts gold and 6 parts by weight of impurities. Divide: 18/24=0.75 mm. Product meets your 750-th sample. Perform a calculation: 20*0,75=15 grams. That's how much pure gold is contained in this ring.