Chemistry- Formulas

Isotopes- Atoms of the same element with a different number of neutrons

Relative Formula Mass (Mr)-Example-Find the Mr of carbon monoxide- COCarbon= 12 Oxygen=1612+16=28Find the Mr of sodium oxide- Na2OSodium= 23 Oxygen= 16(23x2)+16=62Moles-one moleof that substance. For example, the Mr of carbon monoxide (CO) is 28. This means that one mole of carbon monoxide has a mass of 28 g. You should be able to see that: 14 g of carbon monoxide contains 14 ÷ 28 = 0.5 moles 56 g of carbon monoxide contains 56 ÷ 28 = 2 moles

Empirical Formula-Question- 3.2g of sulfur reacts with oxygen to produce 6.4g of sulfur oxide.Use the fact that Ar of sulfur is 32 and Ar of oxygen is 16.Answer- find the mass of each of the elements first.Oxygen= 6.4-3.2=3.2Now divide each of the elements mass by its Ar value.Sulfur: 3.2/32=0.1Oxygen: 3.2/16=0.2Fine the ratios of the elements, you can do this by dividing the smallest of the numbers to give you the number of atoms of each element in the compound.Sulfur: 0.1/0.1=1Oxygen: 0.2/0.1=2(if one of these number ever ends in .5 then multiply both numbers by 2)So this tells us that there is one sulfur and two oxygen's so the formula is SO2

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