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relative formula mass& the mole and mass (the mole is simply the name…
relative formula mass& the mole and mass
you can calculate %mass of an element in a compound
percentage mass of an element in a compound= Ar x number of atoms of that element /Mr of the compound x 100
the mole is simply the name given to an amount of a substance
3) the mass of the number of atoms or molecules of any substances is exactly the same number of grams as the relative atomic mass Ar or relative formula mass Mr of the element or compound
one mole of atoms or molecules of any substance will have a mass in grams equal to the relative formula mass( Ar or Mr ) for the substance
nitrogen gas N2 has a Mr of 28 ( 2x 14) so one mole of N2 weighs exactly 28g
carbon dioxide co2 has an Mr of 44 (12+[2 x 16] so one mole of co2 weighs exactly 44g
carbon has a Ar of 12 so one mole of carbon weighs exactly 12 g
2) one mole of any substance is just an mount of that substance that contains an Avogadro number of particles so 6.02 x 10 to the power of 23 particles the particles can be atoms molecules ions or electrons
5) this means that 12 g of carbon or 28 g of nitrogen or 44g of carbon dioxide all contain the same number of particles namely one mole or 6.02 x 10 to the power of 23a toms or molecules
1) just like a million is this many 1000000; or a billion is this many :1000000000, so the Avogadro constant is this many 620 000 000 000 000 000 000 000 or 6.02 x 10 to the power of 23
FORMULA TO FIND THE NUMBER OF MOLES IN A GIVEN MASS
NUMBER OF MOLES = MASS IN G ( OF AN ELEMENT OR COMPOUND ) / Mr ( OF THE ELEMENT OR COMPOUND )
in a chemical reaction mass is always conserved
3)no mass is lost or gained we say that mass is conserved during a reaction
2Li + F 2 -->2LiF in this reaction there are 2 lithium atoms and 2 fluorine atoms on each side of the equation
2) this means there are the same number and type of atoms on each side of a reaction equation
4)by adding up the relative formula masses of the substances on each side of a balanced symbol equation you can see mass is conserved the total Mr of all the reactants equal the total Mr of the product
1) during a chemical reaction no atoms are destroyed and no atoms are created
if mass changes usually gas is involved
explanation 1
2) before the reaction the gas is floating around I the air its there but its not contained in the reaction vessel so you cant account for its mass
3) when the gas reacts to form part of the product is becomes contained inside the reaction vessel so the total mass of the stuff inside the reaction vessel increases
1) if the mass increases its probably because one of the reactants is a gas that's found in air
when a metal reacts with oxygen is an unsealed container the mass of the continer increases
explanation 2
2) before the reaction all the reactants are contained in the reaction vessel
if the vessel isnt enclosed then the gases can escape from the reaction vessel as they are formed they are no longer contained in the reaction vessel
1)if the mass decreases its probably because one or more of the products are gases and all the reactants are solids liquids or aqueous