chemistry empirical and molecular formulas. objectives n students will be able to: n determine the...
DESCRIPTION
Two types of formulas Empirical Formula n Gives the formula of a compound in the simplest whole number ratio of atoms/moles in a compound Molecular Formula n “True Formula”—gives the actual ratio of atoms/moles in a compoundTRANSCRIPT
ChemistryEmpirical and Molecular Formulas
Objectives Students will be able to: Determine the empirical formula of a
compound Determine the molecular formula of a
compound
Two types of formulasEmpirical Formula Gives the formula of a
compound in the simplest whole number ratio of atoms/moles in a compound
Molecular Formula “True Formula”—gives
the actual ratio of atoms/moles in a compound
B. Empirical Formula
C2H6
CH3
reduce subscripts
Smallest whole number ratio of atoms in a compound
Determine the empirical formulas for each of the following molecular formulas.1. C8H18…..______________2. H2O2……______________3. Hg2Cl2…..______________
4. C3H6…….______________
5. Na2C2O4..._____________6. H2O......________________7. C4H8….._______________8. C4H6…..________________9. C7H12…._______________10. C2H4O2….___________
• C2H9
• HO• HgCl• CH2
• NaCO2
• H2O• CH2
• C2H3
• C7H12
• CH2O
Finding Empirical Formula1. Use the % of each element as its mass in the compound (ex 36.8% N, 63.2%O)
2. Convert mass of each element to moles.
3. Divide moles by the smallest # of moles to find subscripts.
4. If #’s are not whole #’s, multiply subscripts by 2, 3, or 4 to get whole #’s.
B. Empirical Formula Find the empirical formula for a
sample of 25.9% N and 74.1% O.
25.9 g 1 mol14.0 g
= 1.85 mol N
74.1 g 1 mol16.0 g
= 4.63 mol O
1.85 mol
1.85 mol
= 1 N
= 2.5 O
B. Empirical Formula
N1O2.5Need to make the subscripts whole
numbers multiply by 2
N2O5
Steps for finding Molecular Formula1. Determine the empirical formula(either given or you find it)
2. Find the molar mass of the empirical formula3. Divide the Molecular Formula mass (given in problem)
by the EF mass to create a ratio (n).
4. Multiply the EF formula by the whole # ratio (n). n= MFmass molecular formula = (EF)n
EFmass
Molecular formula: can be the same as the empirical formula or a
Whole # multiple of the empirical.
It is the true number of atoms of each element in a compound.
Finding the Molecular Formula
The empirical formula for adipic acid is C3H5O2. The molecular mass of adipic acid is 146 g/mol. What is the molecular formula of adipic acid?Step 1 (given in problem) Determine Empirical Formula
Step 2. Find the Molar mass of CStep 2. Find the Molar mass of C33HH55OO22
3(12.0 g) + 5(1.0) + 2(16.0) = 73.0 g3(12.0 g) + 5(1.0) + 2(16.0) = 73.0 g
Finding the Molecular FormulaThe empirical formula for adipic acid is C3H5O2. The molecular mass of adipic acid is 146 g/mol. What is the molecular formula of adipic acid?
3(12.01 g) + 5(1.01) + 2(16.00) = 73.08 g3(12.01 g) + 5(1.01) + 2(16.00) = 73.08 g
146 273
Finding the Molecular FormulaThe empirical formula for adipic acid is C3H5O2. The molecular mass of adipic acid is 146 g/mol. What is the molecular formula of adipic acid?
3(12.01 g) + 5(1.01) + 2(16.00) = 73.08 g3(12.01 g) + 5(1.01) + 2(16.00) = 73.08 g
146 273
Step 4. Multiply the empirical formula by this number to get the molecular formula.
(C3H5O2) x 2 = C6H10O4