Chapter 3. Calculations involving Chemical Formulae and Equations. Contents. Mass and Moles of a Substance Molecular weight Moles Determining Chemical Formulae Mass % from formula Elemental Analysis: gives % C, H, O Determining formula from elemental analysis Stoichiometry
Calculations involving Chemical Formulae and Equations
fm = formula mass
= aMA + bMB + cMC + dMD + ...
1 mol of
E.g. Determine the mass of NaCl needed to have 5.0 mol of it.
E.g. Determine the number of mol of NaCl in 15.00 g of it.
E.g. Determine the number of molecules in 3.222 mol of NaCl
E.g. Determine the number of atoms in 4.32 g of NaCl
E.g. Determine the mass of one formula unit of NaCl.
Empirical Formula: Simplest formula where all coefficients are integers.
Mass%O = 34.7%
Mass%C = 52.1%
Mass%H = 13.1%
Mass of H2O = 1.902 g.
The relative amounts of reactants and products in a reaction are given by the ratio of stoichiometric coefficients. (Conservation of mass).
E.g. Determine the mass of Na needed to react with 34.45 g of Cl2 and the maximum mass of NaCl that could be produced.
Let n = mol; FM = formula mass then
E.g. 1: Determine the mass of oxygen consumed when it reacts with 10 g CH3CHO.
E.g. 2. Calculate the mass of oxygen needed to react with 100 g Al to for Al2O3.
E.g. 1 Determine limiting reagent if 3.00 moles of Al react with 2.15 moles of O2 to form Al2O3.
E.g.2 Calculate the theoretical yield when 20 g Al react with 25 g O2.
CH3OH(l) + CO(g) HC2H3O2(l)
aA + bB cC