Module 2: Chapter 3 (Amount of substance)
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How is mol calculated?
amount, n = mass, m / molar mass, M
How is the number of ‘particles’ calculated?
n x Na (6.02 x 10^23)
What is the molecular formula?
the number of atoms of each element in a molecule
What is the empirical formulae?
the simplest whole-number ration of atoms in each element in a compound
What is the water of crystallisation?
• Many crystalline solids are hydrated, water molecules are incorporated into their crystalline structure • this water is known as the water of crystallisation
What is the approach to calculating the formula of a hydrated solid?
• subtract mass of crucible & anhydrous salt from mass of crucible; hydrated salt and use answer to calculate the moles of water • subtract the mass of crucible from mass of crucible & anhydrous salt and use the answer to calculate the number of moles in the salt • divide the moles of water by the moles of the compound
What is the equation to calculate mol of a gas at RTP?
mol (n) = volume of gas (dm^3) / 24dm^3
What is the ideal gas equation?
pV = nRT p -> pressure (Pa) V -> volume (m^3) n -> moles of gas R -> ideal gas constant (8.314) T -> temperature (Kelvin)
How do you convert between Pa and KPa?
Pa -(÷1000)-> KPa KPa -(x1000)-> Pa
How do you convert between cm^3, dm^3 and m^3?
cm^3 -(÷1000)-> dm^3 -(÷1000)-> m^3 m^3 -(x1000)-> dm^3 -(x1000)0-> cm^3 cm^3 -(÷1 000 000)-> m^3 m^3 -(x1 000 000)-> cm^3
How do you convert between K and Celsius?
C -(+273)-> K K -(-273)-> C
What is the concentration of a solution?
The concentration of a solution tells us the amount of solute in a particular volume of solution
How is concentration calculated?
concentration (moldm^-3) = mol (n) / volume (dm^3)
How do you convert between conc in gdm^-3 and moldm^-3?
gdm^-3 -(÷Mr)-> moldm^-3 moldm^-3 -(xMr)-> gdm^-3
What is meant by the ‘amount of substance’?
• n - counts the number of particles in a substance measured in the unit mole, mol.
Explain what a mole is
One mole is the amount of a substance that contains 6.02x10^23 particles (Avogadro constant)
What is Avogadro’s constant?
Is 6.02x10^23 mol^-1, the number of particles in each mole of carbon-12 - C-12 is the standard measurement of relative atomic masses
What is Molar Mass, M?
• molar mass is the mass per mole of a substance - the units of molar mass are gmol^-1
What is molar gas volume?
• the molar gas volume Vm is the volume per mole of gas molecules at a stated temperature and pressure • volume of gas depends on the pressure and temperature, most experiments are at RTP
What is meant by RTP?
• RTP is about 20 degrees celcius and 101 kPa (1 atm) • at RTP 1 mole of gas molecules has a volume of approx 24.0 dm^3 • therefore at RTP the molar gas volume = 24.0 dm^3
What is meant by the term hydrated?
a crystalline compound containing carbon and hydrogen only
What does anhydrous mean?
containing no water molecules
How do you calculate percentage yield
actual yield / theoretical yield x100
Why is theoretical yield hard to achieve?
• reaction may not have gone to completion • other reactions may have taken place alongside the reaction (side reactions) • purification of the product may result in the loss of some product