Write the formulas that go with the following names: Warm-Up Write the formulas that go with the following names: Tricarbon Pentaoxide Osmium (III) Sulfide Magnesium Nitride Dinitrogen Tetraoxide Lead (IV) Fluoride Calcium Bromide Pentacarbon Hexaphosphide
Chemistry: Empirical Formula Moles Whitaker 21 October 2013
Empirical formula is the simplest chemical formula Ex. CH4
Calculating the empirical formula from the percent composition Steps Assume the percent = grams. Convert each amount of grams to moles. Divide each number of moles by the smallest number of moles. If all the numbers are not whole numbers, multiple everything by a number that will get you a whole number. (This may take a few tries!) The whole numbers become subscripts in the formula.
Percent to mass Mass to mole Divide by small Multiply ‘til whole
Example A compound is 32.38% sodium, 22.65% sulfur, and 44.99% oxygen. What is the empirical formula?
Example 2 A compound is 40.0% Carbon; 6.71% Hydrogen; 53.29% Oxygen. What is its empirical formula?
Practice 89.94% C; the rest is H 56.34% P; 43.66% O 43.64% P; 56.36% O 56.34% P; 43.66% O 43.64% P; 56.36% O 40.9% C; 4.58% H; 54.5% O
Molecular Formula Molecular formula is the chemical formula that can be reduced. Molecular Formula- the formula for a compound in which the subscripts give the actual number of each element in the formulas it truly exists. Ex. C2H8
Molecular Formula Empirical Formula H2O CH3COOH CH2O C6H12O6 Notice two things: 1. The molecular formula and the empirical formula can be identical. 2. You scale up from the empirical formula to the molecular formula by a whole number factor. Molecular Formula Empirical Formula H2O CH3COOH CH2O C6H12O6
Now, finding the molecular formula Find the empirical formula Calculate the molar mass (formula mass) Divide the given mass of the substance by the molar mass Multiply each subscript of the empirical formula by the answer to #3
Example You have 56.106 grams of a substance with an empirical formula of CH2. What is the molecular formula?