iiiiii formula’s the mole. formulas n molecular formula = (empirical formula) n n molecular...
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I II III
Formula’s
The Mole
Formulas
molecular formula = (empirical formula)n molecular formula = C6H6
empirical formula = CH
Empirical formula: the lowest whole number ratio of atoms in a compound.
Molecular formula: the true number of atoms of each element in the formula of a compound.
Formulas (continued)
Formulas for ionic compounds are Formulas for ionic compounds are ALWAYSALWAYS empirical (lowest whole number empirical (lowest whole number ratio).ratio).
Examples:Examples:
NaCl
MgCl2
Al2(SO4)3
K2CO3
Formulas (continued)
Formulas for molecular compounds Formulas for molecular compounds MIGHTMIGHT be empirical (lowest whole be empirical (lowest whole number ratio).number ratio).
Molecular:Molecular:
H2O
C6H12O6 C12H22O11
EmpiricalEmpirical::
H2O
CH2O C12H22O11
Empirical Formula
Empirical comes from Latin empiricus meaning a doctor relying on experience. An empirical formula must be obtained from experimental data.
The percent composition of a compound is the data you need to calculate the basic ratio of the elements contained in the compound.
The basic ratio, is called the empirical formula, gives the lowest whole-number ratio of the atoms of the elements in a compound.
Empirical Formula
C2H6
CH3
reduce subscripts
Smallest whole number ratio of atoms in a compound
Empirical Formula…how to find it!
1. Find mass (or %) of each element.
2. Find moles of each element.
3. Divide moles by the smallest # to find subscripts.
4. When necessary, multiply subscripts by 2, 3, or 4 to get whole numbers’s.
Empirical Formula
Find the empirical formula for a sample of 25.9% N and 74.1% O.
25.9 g 1 mol
14.01 g = 1.85 mol N
74.1 g 1 mol
16.00 g = 4.63 mol O
1.85 mol
1.85 mol
= 1 N
= 2.5 O
Empirical Formula
N1O2.5Need to make the subscripts whole
numbers multiply by 2
N2O5
Molecular Formula “True Formula” - the actual number
of atoms in a compound
CH3
C2H6
empiricalformula
molecularformula
?
Molecular Formula1. Find the empirical formula.2. Find the empirical formula mass.3. Divide the molecular mass by the empirical mass.4. Multiply each subscript by the answer from step 3.
nmass EF
mass MF nEF
Molecular Formula The empirical formula for ethylene is
CH2. Find the molecular formula if the molecular mass is 28.1 g/mol?
28.1 g/mol
14.03 g/mol = 2.00
empirical mass = 14.03 g/mol
(CH2)2 C2H4