Chapter 3 - Amount of Substance Flashcards
Amount of substance and the mole, Determination of formulae, Moles and volumes and Reacting quantities
What is Avogadro’s Constant?
The number of atoms in one mole of the carbon-12 isotope. found in data sheet 6.02X10^23
What is a mole?
The amount of any substance containing as many particles as there are particles in 12g of the carbon-12 isotope.
What is the equation for the number of moles of a substance?
n=m/Mr
n - number of moles (mol)
m - mass (g)
Mr - molar mass (g/mol)
What is relative formula mass?
The weighted mean mass of the formula unit of a compound compared with 1/12th of an atom of carbon-12
What is the molecular formula?
The number of atoms of each element in a molecule.
What is the empirical formula?
The simplest whole-number ratio of atoms of each element in a compound.
How is the empirical formula found?
E Element
M Mass or %
--- ----------------
M Molar mass
A Answer (moles)
------------------------
Smallest answer
R RatioHow is the molecular formula found?
Find empirical formula.
Divide molar mass of a molecule by molar mass of empirical formula.
Multiply empirical formula by the result.
What is relative molecular mass?
The mass of a molecule compared with the mass of an atom of carbon-12.
In hydrated salts, what is the name given to water molecules?
Waters of crystallisation
What is the concentration of a solute?
The amount of solute (in moles) dissolved in each 1dm^3 of solution
What is the equation for finding a solution’s concentration?
c=n/v
c - concentration (mol/dm^3)
n - number of moles (mol)
v - volume (dm^3)
What is molar volume?
The volume per mole of a gas.
Measured in dm^3/mol
What is the value of molar volume at room temperature and pressure?
1 mole of any gas takes up 24 dm^3/mol at rtp
What is the equation for molar volume?
mgv=V/n
mgv - molar gas volume (dm^3/mol)
n - number of moles (mol)
V - volume (dm^3)
What are the assumptions made about an ideal gas?
Random motion
Elastic collisions
Negligible size
No intermolecular forces
What is the equation for the ideal gas law?
pV=nRT p - pressure (Pa) V - volume (m^3) n - number of moles (mol) R - ideal gas constant (J/mol/K) T - temperature (K)
What are the standard conditions?
298K or 25C
101kPa or 1 atm of pressure
What is stoichiometry?
The balancing numbers giving the ratio of the amount, in moles, of each substance in a balanced equation.
What are the balanced equations used to find?
The quantities of reactants required to prepare a required quantity of a product.
The quantities of products that should be formed from certain quantities of reactants.
What is the percentage yield?
The actual yield divided by the theoretical yield expressed as a percentage.
(actual yield / theoretical yield ) X100
Why is the theoretical yield so hard to achieve?
The reaction is incomplete.
Competing side reactions giving different products.
Loss of product in handling and purification.
Reversible reaction.
What is the limiting reagent?
The reactant that is not in excess.
What is atom economy?
The molar mass of desired products divided by the sum of the molar masses of all products expressed as a percentage.
(mr of desired products/ mr of total products) X100
What are the benefits of a high atom economy?
Produce a larger proportion of desired products and few waste products.
Important for sustainability, the best use of natural resources.
