3.1 Physical Chemistry: .2 Amount of Substance Flashcards
what is the relative atomic mass?
the average mass of an atom compared with 1/2 of the mass of carbon12 atom
why is carbon12 used as the comparison rather than hydrogen for relative atomic mass?
because the mass of carbon12 Is more accurate than the mass for hydrogen
what is the relative molecular mass? how do you calculate?
the average mass of a molecule compared with 1/2 of the mass of a carbon12 atom. It is calculated by adding together relative atomic mass of each element
what is the relative molecular mass?
what is the equation for finding the number of moles?
no. of moles= mass/rmm
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how do you calculate the number of particles in a substance?
number of particles= (masss/molar mass) x (6.02 x 10^23)
what is the Avogadro’s constant
6.02 x 10^23
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how do you calculate a reacting mass question?
1.) Find the moles of the known chemical 2.) Find the ratio for substance that you’re look for the unkown mass so that you can link the moles to it 3.) Once you have the moles of the substance you don’t have a mass for do another moles=mass/rmm bu rearrange so that mass is the subject
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what is the formula for finding moles from concentration and volume?
mole= C x V
what is the unit for concentration?
dm-3
if you are finding the volume;
you multiply your concentration by a 1000
what is the unit for volume?
cm3
so when you are finding the concentration;
you divide the volume by a 1000
how do you work out the volume?
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what is the empirical formula?
it is the simplest ratio of the atoms of each element in a compound.
what is the molecular formula?
the actual number of atoms of each element in the compound
how do you find the empirical formula?
!. state the elements in the chemical 2. find the moles of those elements 3. divide their moles by the smallest amount (of moles you got) 4. you should have a ratio and this will give you the number of each element in the empirical formula (if you have a ratio where you come out with 1.50 times it by 2 and the other number by 2 so you get all round whole numbers)
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why may you never get 100% yield when making a chemical?
-chemicals can be lost in the process e.g gases might escape, chemicals may not be transferred from one piece of apparatus to the next e.g through filtering and some chemicals may not fully react
what is the theoretical yield?
the mass of product that should be formed in a reaction
what is the equation for percentage yield?
-percentage yield= actual mass/theoretical mass x 100
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what is the equation for working out the moles of a volume of gas in cm3 and dm3
-dm3; moles = V/24 -cm3; moles = v/ (24/1000)
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state the ideal gas equation, state each symbol represents and its required unit
PV=nRT -P= Pressure (Pa) so (kPa —> 1000 x Pa) -V= volume (m3) so (dm3—> m3/ 1000) (cm—> m3/1,000,000) -n= no. of moles -R= Gas constant
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