Chemical calculations - both Tiers
For your exam, you will need to know what relative formula mass is - and be able to work out the relative formula mass of a compound [compound: A compound is a substance formed by the chemical union (involving bond formation) of two or more elements. ] when given its formula.
To find the relative formula mass (Mr) of a compound, you just add together the Ar values for all the atoms in its formula.
The relative formula mass of a substance, shown in grams, is called one mole of that substance. So one mole of carbon monoxide has a mass of 28g, and one mole of sodium oxide has a mass of 62g.
The table shows some more examples of relative formula mass calculations, using the relative atomic mass values given at the bottom of the page.
|Water||H2O||1 + 1 + 16 =||18|
|Sodium hydroxide||NaOH||23 + 16 + 1 =||40|
|Magnesium hydroxide||Mg(OH)2||24 + 16 + 16 + 1 + 1 = (remember that there are two of each atom inside the brackets)||58|
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