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/molecules in 1 mole of a substance (6.02x10^23)
What equation links mass, molar mass, and the number of moles?
n=m/M
n - number of moles (mol)
m - mass (g)
M - molar mass (gmol^-1)
What is relative formula mass?
The weighted mean mass of a formula unit of a compound compared to 1/12th the mass of an atom of carbon-12
What is a molecular formula?
The actual number of atoms of each element in a molecule
What is an empirical formula?
The simplest whole-number ratio of atoms of each element in a compound
How is the molecular formula for a compound found?
• Find the empirical formula.
• Divide the M of the molecule by the M of the empirical formula.
• Multiply the 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 (mol) dissolved in each 1dm^3 of solution
What equation links concentration, volume, and number of moles?
What is molar volume?
The volume occupied by 1 mole of a gas (dm^3mol^-1)
What is the value of the molar gas volume at RTP?
24dm^3mol^-1
What equation links molar gas volume, volume, and number of moles?
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 (Jmol^-1K^-1)
T - temperature (K)
What is stoichiometry?
The ratio of the amount, in moles, of each substance in a balanced equation
Formula for percentage yield
Why is the theoretical yield rarely achieved?
• The reaction is incomplete
• Competing side reactions yielding different products
• Loss of product in handling and purification
• Reversible reaction
What is the limiting reagent?
The reactant that is not in excess
Formula for % atom economy
What are the benefits of a high atom economy?
• Produce a larger proportion of desired products (fewer waste products)
• Important for sustainability (the best use of natural resources)
What is a standard solution and how is it prepared?
A standard solution is a solution of known concentration
• An exact mass of a solute is dissolved in a solvent
• The solution is made up to an exact volume using distilled water in a volumetric flask
Formula for percentage error:
