Moles
description
Transcript of Moles
Moles
Definition• A mole is the mass of a substance
which contains the same number of particles as 12 grams of the isotope carbon12.
• These particles could be atoms, ions or molecules.
• 12 grams of carbon12 contain 6.02 x1023
atoms• This number is the Avogadro Constant,
and is given the symbol L.
Eg; One mole is…
27g of aluminium63.5g of copper
16 + 2 = 18g of water
Calculating the number of particles
• Number of particles = moles x Avogadro Constant.
• Eg; How many particles are there in 0.1 moles of hydrogen?
• N = 0.1 x 6.02x1023 = 6.02 x 1022
molecules.
Calculating the number of moles
• Moles = number of particles / Avogadro constant.
• Eg; How many moles of methane are there in 3.01 x1023 molecules?
• Moles = 3.01x1023 / 6.02x1023 = 0.5 moles.
Calculating the molar mass• One mole of an element has a mass
equal to the relative atomic mass in grams.
• Eg; the mass of one mole of sodium is 23g.
• The mass of one mole of a compound is found by adding together the masses of all its elements in the correct ratio.
• Units gmol-1
• Eg; What is the molar mass of calcium carbonate?
• Write the formula; CaC03.• M = RAMCa + RAMC + 3xRAMO.• M = 40 + 12 + 3x16 = 100g
Calculating the number of moles• No moles = mass / RAM• Eg; How many moles are there in
4g of calcium.• Look up the mass number of
calcium in the periodic table.• The atomic mass is the mass
number in grams. • N = 4 / 40 = 0.1 moles
Number of moles
Mass (g)
Relative atomic mass
n
m
RAM
Think of the equation as a triangle
Number of moles =
mass (g)
Relative atomic massn
m
RAM
n = m / RAM
Rearranging;
Calculating the number of moles of a compound.
• No moles = mass / Mr• Eg; How many moles are there in 15g of
calcium carbonate?• Look up the Ars, then add them
together to find the Mr.• Mr = 40 + 12 + (16 x 3) = 100• One mole has a mass of 100g.• N = 15 / 100 = 0.15 moles.
Number of moles
mass =
n
m
RAM
m = nRAM
X RAM
Rearranging;
Calculating the mass from moles• Mass = No moles X Ar• Eg; What is the mass of 0.75 moles of
sodium?• Ar = 23• Mass = 0.75 x 23 = 17.25g• Similarly for a compound;• Mass = No moles X Mr• Eg; What is the mass of 0.8 moles of
sodium chloride?• Mr = 23 + 35.5 = 58.5• Mass = 0.8 x 58.5 = 46.8g