M5 - What is a substance made of?
- Using the C-12 isotope, we assigned the mass of 1 proton or 1 neutron to be 1 amu.
- This determination allowed the masses of all elements to be assigned in amu.
- Avogadro discovered a relationship between volume and number of gas particles.
- Chemists determined the number of particles required to have the mass of the substance be equal to the atomic mass in grams = Avogadro's number (6.02 x 10^23)
- One mole = 6.02 x 10^23
- Convert moles to grams and grams to moles
- Calculate % composition
- Steps to find the empirical formula of a substance
- Find the mass of each element present in the compound (decomposition or single replacement reaction)
- AB -> A + B (measure masses of A and B)
- AB + C -> AC + B (measure mass of AB, mass of B, and subtract mass of AB from the mass of B to get the mass of A)
- Convert mass to moles
- Divide by the smallest number to calculate the ratio of elements
- Assign these whole number ratios as subscripts to write the empirical formula
- Steps to find the molecular formula of a substance
- Obtain a known mass of the substance
- Convert the substance to a gas
- Record the T, P, and V
- Use PV = nRT to calculate the number of moles (n)
- Calculate mass (g)/number of moles = molar mass
- Calculate the (molar mass of the substance)/(molar mass of empirical formula) = multiplier
- Multiply the subscripts of the empirical formula by the multiplier to write the molecular formula
- Determine the limiting reactant - the reactant that "runs out" in a reaction.
- Determine the % yield
% Yield = (Actual mass of product)/(Theoretical mass of product) x 100
