2.3 Amount of Substance Flashcards
What is a mole ?
Amount of any substance certaining as many particles as there are carbon atoms in 12g of carbon-12.
What is Avogadro’s constant ?
6.02x10^23
It is the number of atoms per mole of carbon-12.
What is molar mass ?
It is the mass per mole of a substance (g/mol-1)
How to work out number of moles?
Mass (g) / molar mass (g/molar-1)
How to work out number of particles ?
Number of moles x Avogadro’s constant
What does 1 mole of gas at room temperature and pressure obtain?
24 dm^3 (24dm^3 = 24000cm^3)
Molecular Formulae
Number of atoms of each element in a molecule.
Empirical Formula
Simplest whole number ratio of atoms of each element in a compound.
How to calculate empirical formula ?
1) Mass/molar mass = no of moles.
2) Divide by smallest number.
3) Make a whole number ratio.
4) Create formula.
Relative molecular mass
Compares mass of molecule with mass of an atom of carbon-12.
Relative formula mass
Compares mass of formula unit to that of an atom of carbon-12.
Why are many coloured salts hydrated ?
This is because water is a part of their crystalline structure. This water is known as the water of crystallisation.
What happens when copper (II) sulphate salt is heated ?
Water bonds within the crystal are broken and water is driven off leaving behind the white anhydrous powder.
Equation for copper (II) sulphate reaction
CuSO4.5H2O = CuSO4 + 5H2O
What happens to heated CuSO4 when no water is returned ?
Crystalline structure is lost and white anhydrous powder remains.
Equation for volume
Volume = number of moles x 24 dm^3
What is the ideal gas equation ?
pV = nRT
P= pressure 1atm = 101000pa
V = volume 1dm = 1000cm
N = no of moles (mol)
R = molar gas constant =8.314 mol-1
T= temp(•c) +273 = kelvin
What is concentration ?
Concentration is the number of moles of a solute dissolved in 1dm^3 of a solution.
What is the equation for finding concentration?
concentration= Mass or Moles / Volume
What is a standard solution?
A solution with a known concentration.
What is the molar gas volume ?
Volume per mole of gas molecules at standard temperature and pressure.
Equation for Molar gas volume
number of moles= volume/molar gas volume
What is the stoichiometry ?
The ratio of number, from balanced equation, of the amount of moles of each substance.
What is percentage yield ?
% of a desired product.
What is theoretical yield ?
Maximum possible amount of product that can be produced.
What is actual yield ?
How much product is actually produced from a reaction. Usually lower than theoretical yield.
Equation for percentage yield
%=actual yield/theoretical yield x 100
What are excess and limiting reagents ?
Limiting reagent is reactant not in excess that gets used up first in reaction.
How to find limiting reagent ?
1) Find moles of each reactant in equation.
2)Find smallest amount of moles.
3)Use mole number to find amount of moles for other products based on stoichiometry.
What is atom economy ?
Atom economy is a measure of how well the atoms have been utilised.
Equation for atom economy
sum of desired amount/ sum of molar mass of all x 100
Why are high atom economies good ?
Means reaction produced large quantities of desired product, with little waste products being made. More sustainable as it makes most use out of natural resources used.
