2.3 AMOUNT OF SUBSTANCE Flashcards
What is carbon-12?
Carbon-12 is the standard isotope used to base all atomic masses on
What is Avogadro’s constant?
Avogadro’s constant is the number of particles per mole of substance.
6.02x10^26
What is amount of substance?
Amount of substance is a quantity used to count the number of particles in a substance, measured in moles
What is molar mass?
Molar mass is the mass of 1 mol of substance measured in g/mol
What is the equation linking moles, mass and molar mass?
Amount of substance (mol) = mass (g) / molar mass (g)
What is the molecular formula?
The molecular formula is the number of atoms of each element in a molecule
- O2, CO2, P4
What is the empirical formula?
The empirical formula is the simplest whole number ratio of atoms or ions of each element in a compound
- Mg, C, NaCl
What is relative molecular mass?
Relative molecular mass compares the mass of a molecule with the mass of an atom of carbon-12
What is relative formula mass?
Relative formula mass compares the mass of a formula unit with the mass of an atom of carbon-12
What is water of crystallisation?
Water of crystallisation is water molecules that are bonded into a crystalline structure of a compound
What are hydrous and anhydrous?
Hydrous- contains water molecules
Anhydrous- does not contain water molecules
What equation links moles, concentration and volume?
Moles (mol) = concentration (mol/dm3) x volume (dm3)
What does Avogadro’s law state?
Avogradro’s law states that equal volumes of gases at the same temperature and pressure contain an equal number of moles
What equation links moles, volume and molar gas volume?
Moles (mol) = volume (dm3) / molar gas volume (24dm3/mol)
What is the ideal gas equation?
The ideal gas equation is:
pressure (Pa) x volume (dm3) = moles (mol) x gas constant (8.31 J/mol/K) x temperature (K)
What does it mean to behave like an ideal gas?
To be an ideal gas, gases must:
- have no forces between particles
- have a negligible size of particles
Why do we not get 100% product yield?
Why we don’t get 100% product yield:
- reaction may not go to completion
- other reactions may have taken place
- purification may result in loss of product
What is the equation for percentage yield?
Percentage yield = actual yield / theoretical yield x 100
What is the limiting reagent and reagent in excess?
Limiting reagent and reagent in excess:
- one reactant is usually in excess (more of it than needed)
- limiting reactant will be used up and once done the reaction will stop
- limiting reactant determines how much product will form
What is atom economy?
Atom economy measures how well atoms of the reactants have been put to use
- assumes 100% yield
- products of which are not desired and have to be disposed of are called waste products
- products which are not desired but can be sold or utilised elsewhere are called by-products
What is the equation for atom economy?
Atom economy = molar mass(es) of desired product(s) / molar masses of all products
Why should atom economy be improved?
Atom economy should be improved because:
- improves efficiency of process
- reduces waste
- preserves raw materials
- increases sustainability (meeting the needs of today without compromising the ability for future generations to meet their needs)
