chem test 4_ stoichiometry%2Fcalculations .pdf

# To solve 1 put one mole of that element over the gram

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- To solve 1. Put one mole of that element over the gram formula mass of that element 2. Multiply by the given value→ which will give u the value of moles of that element - Example: how many moles of H2 are present in 25 grams of H - 1 MOL H2/ 2 g H2 multiplied by 25 g H2= 12.5 mol H2 How can we calculate the percent composition of each element in a compound? - Total= whole - Part(mass of element)/whole(mass of compound) multiplied by 100 - Example - NH3- N= 14 g 3H= 3 g in all its 17 g - Nitrogen percent composition - 14/17 multiplied by 100= 1400/17 - Hydrogen percent composition - 3/17 multiplied by 100= 300/17 Molecular Formula - Indicates the total number of atoms of each element needed to form the molecule - Actual ratio atoms Empirical Formula - Simplest whole number ratio in which atoms combine to form a compound - Example: C6H12O6→ RATIO 6,12,6 - Simpler: CH20 → RATIO 1,2,1 How to find molecular formula given empirical formula? 1. Find the mass of the empirical formula (CH=13g)

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2. Divide the mass of molecular formula (given) by the mass of the empirical formula (26/13) 3. Multiply the empirical formula by the answer found (CHx 2=C2H2) How do we calculate empirical formula?
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