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Cards In This Set
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Relative atomic mass, Ar
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*average mass of a single atom of an element compared with Carbon-12. Ar O = 16
*the larger number on the periodic table *the number of protons and neutrons added together |
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Relative molecular mass, Mr
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Average mass of all the atoms in a molecule added together
Mr CO2 = 44 Mr O2 = 32 * the mass of one mole of this substance |
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Relative formula mass, Mr
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Average mass of all the atoms in an ionic compound added together
Mr CaCO3 = 100 * the mass of one mole of this substance |
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C + O2 --> CO2
How many grams of CO2 are made from 12 g of carbon and 32g of oxygen? |
The total mass on each side is the same. So 44g of CO2 is made.
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How do you calculate the number of moles, n, form the number of grams of a substance?
e.g. 10g of CaCO3 |
You need to determine the Mr or the mass one mole weighs
mass in g/Mr = n |
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How much does one mole of a substance weigh?
e.g. CuSO4 |
The same as its Mr, the mass of all the atoms in the formula added together
Ar: Cu = 64, C=12, O=16 Mr = 64+12+64=140 To get one mole of CuSO4 you need to weigh out 140g of it. |
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What volume does one mole of gas occupy when at room temperature and pressure? (rtp = 20oC and 1atm)
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One mole of any gas at rtp ( e.g. Ar,H2 or CO2) occupies 24dm3, this is the same as 24 litres or 24,000 cm3
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One mole contains how many particles of that substance?
triple only |
It contains a huge (but always the same) number of particles, called Avogadro's number 6.02x1023
triple only |
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Calculate the relative atomic mass of Chlorine from its isotopes. The abundances are Cl 35 75% and Cl 37 25%
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35x0.75 + 37x0.25 = 35.5
or 35x75/100 + 37x25/100= 35.5 |
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What is the % of element N in NH4NO3?
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Determine the total mass of N
mass N 2x14=28 and the Mr of the formula Mr= 80 Ar/Mr x100 = 28/80x100= 35% |
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Calculate the % composition of methane. CH4
%C = %H = The composition of any pure substance is always the same. |
Mr = 12+4= 16
% C: 12/16x100= 75% % H: 4/16x100= 25% |
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The molecular formula of a substance tells us..
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The total number of atoms in the molecule
e.g. hexane C6H14 |
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The empirical formula tells us ..
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The simplest ratio of atoms in the molecule
e.g ethane CH3 (molecular formula is C2H6) |
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What is the concentration of a solution in moles per litre?.
e.g. 2.5 g of copper sulfate in 1 dm3 |
First convert g to moles
!! copper sulfate has 5 waters of crystallisation !! CuSO4.5H2O Mr = 250 mass/250=n 2.5/250=0.01mols 0.01 mols in one litre is also written as 0.01M. 'zero point zero one molar' |
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What is the volume of 0.25 moles of CO2?
triple only |
Vol at rtp = n/24dm3
0.25x24dm3= 6 dm3 or 6000cm3 triple only |
