Biology Notes

Topics: Oxygen, Chemistry, Hydrogen Pages: 2 (341 words) Published: December 13, 2012
Molecular formula from empirical formula
1) There is a whole number multiple of the empirical formula in the molecular formula MF – (EF) n Molar mass/ empirical formula mass = n
1) In a combustion reaction an organism sample is burned in the presence of oxygen and produces CO2 and H2O as main products. 2) A hydrocarbon is a molecule that contains only carbon and hydrogen 3) Combustion analysis of naphthalene, a hydrocarbon used in mothballs, produced 8.80g CO2 and 1.44 H2O. Calculate the empirical formula for naphthalene. 8.80g CO2 (find moles of Carbon by dividing the molar mass and doing the molar ratio of C and CO2 = 0.200mol C. 1.44H2O (find moles of Hydrogen by dividing the molar mass of water and doing the ratio of 2moil H/1molH2O) 0.160mol H divide them by the smallest number of moles

C = 1.25
H= 1
Multiply 4= 5, H=4
1) If the molar mass of naphthalene is 128.18g/mol what is the molecular formula of naphthalene? C5H4 = 64.093g/mol
Summary of process for determining molecular formulas
1) Find the mass of each element present
2) Change mass to moles
3) Find the mole ratio
4) Change to a whole number ratio for the empirical formula 5) Use the molar mass and the empirical formula mass to determine the number of empirical formula units in the molecule. Wiring and balancing chemical equation

1) chemical equations: a representation of the chemical reaction taking place, reactants are being converted into products. 2) Takes advantage of the law of conservation of mass.
3) The number and identities of the atoms on the reactants side should be the same as the number and identities of the atoms on the products side. Why do we balance equations?
1) to know the appropriate ratios to mix reactants
2) to predict the appropriate amounts of products produced. Writing and balancing chemical equations
1) always balance with whole numbers! Cannot have frations...
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