Types of Chemical Formulas

Types of Chemical Formulas Molecular number of atoms present in the smallest particle of that compound C6H12O6 Empirical simplest whole number ratio of atoms in a compound CH2O

just reduce or simplify the coefficients as you would a fraction. To go from molecular C6H12O6 to empirical CH2O as seen on the last side….. just reduce or simplify the coefficients as you would a fraction. Keep in mind: the coefficients must be in the same ratio. C6H12O6 all coefficients are divisible by 2.

Determine Empirical Formula from Mass Ratio of Elements A compound consists of 24g C and 64g O What is the empirical formula of the compound? Step 1 Change the masses to moles. The number of moles of each element are your subscripts

24g C ÷ 12g C = 2.0mol C 64g O ÷ 16g O = 4.0mol O So make these your subscripts…… C 2.0 O 4.0

CO2 Step 2 subscripts must be smallest whole numbers C 2.0 O 4.0 reduces to CO2

Practice…what is the empirical formula? A pure sample contains 14g N and 8g O A compound consists of 36.0g C and 12.0g H A substance consists of 52g Cr and 24g O N2O CH4 Cr2O3

Practice…what is the empirical formula? A pure sample contains 14g N and 8g O 14g N ÷ 14g N = 1 mol N 8gO ÷ 16g O = 0.5 mol O A compound consists of 36.0g C and 12.0g H 36g C ÷ 12g C = 3 mol C 12g H ÷ 1g H = 12 mol H A substance consists of 52g Cr and 24g O 52g Cr ÷ 52g Cr = 1 mol Cr 24gO ÷16g O = 1.5 mol O N2O CH4 Cr2O3

Finding Molecular Formula from Empirical Formula Empirical formula: CH3 If the molecular mass of the substance is 30g what is the molecular formula? Step 1: make a list of possible molecular formulas CH3, C2H6, C3H9, C4H12 …..

Step 2: Determine molar masses of your list of molecules. Step 3: whichever matches is your answer C2H6 2(C) x12 = 24g + 6(H) x 1 = 6g 30g

Practice A 39g sample of a gaseous substance contains 18g C and 21g nitrogen What is the empirical formula? CN If the molecular mass = 52g what is the molecular formula? C2N2

What is the empirical formula of a hydrocarbon that consists of 84g carbon and 14g hydrogen? CH2 If its molar mass is 112g, what is its molecular formula? C8H16

A compound known as a hydrate has the formula: K2CrO4∙ 6H2O A compound known as a hydrate has the formula: K2CrO4∙ 6H2O. What percentage of this compound is water? 36%  

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