empirical formula and molecular formula

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Empirical Formula and Molecular Formula. For Ionic cmpds we can predict formulas based on common ion charges Sodium + Oxygen together Na + O 2-  Na 2 O For molecular cmpds, charges are not involved, and this makes it harder to predict. If you know the % comp it can be done!!. - PowerPoint PPT Presentation

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• EMPIRICAL FORMULA AND MOLECULAR FORMULA

• For Ionic cmpds we can predict formulas based on common ion charges

Sodium + Oxygen togetherNa+ O2- Na2O

For molecular cmpds, charges are not involved, and this makes it harder to predict. If you know the % comp it can be done!!

• EMPIRICAL FORMULASmallest whole number ratio of elements in a cmpd. (not necessarily the real formula!!)

• Real FormulaE.F. H2O H2OC6H12O6 CH2O Can be same!

• STEPSChange % to gramsChange grams to moleDivide all by smallest number of molesUse answers from step 3 as subscripts

• WHAT IS THE EMPIRICAL FORMULA FOR A COMPOUND THAT IS 79.9% C AND 20.1% H 1) 79.9% 79.9g+20.1% +20.1g100% 100.0g2) 3) 79.9g x 1 mol = 6.66mol C 6.66 = 1 12gC 20.1 g x 1 mol = 20.1 mol H 6.66= 3 1gH4) CH3

• Find the empirical formula for a cmpd that is 54.5gC, 13.6gH, 31.8gN

• Find the empirical formula for a cmpd that is 54.5gC, 13.6gH, 31.8gN

54.5gC x 1molC = 4.54molC 12g13.6gH x 1 mol H = 13.6molH 1g 31.8gN x 1mol N = 2.27mol N 14g 2.27 =22.27 =62.27 =1C2H6N

• MOLECULAR FORMULAThis formula has the actual number of atoms in the cmpd. (the EF could be the same or have less atoms)

• STEPSFind molar mass of the E. F. Divide M.F.s molar massE. F. molar mass 3) If greater than 1, multiply all the subscripts in the E.F. by your answer in # 2Given in problem

• EX. What is the M.F. if: NO2 = E.F Molar mass is 92g/mol

• M.F.S MOLAR MASSE. F. MOLAR MASS 92 (MF)(14+2(16)= 46 (EF) =2

NO2 becomes N2O4