Determining Chemical Formulas 7-4

Beaker Breaker Name or write the following formulas: 1.AlN =___________________ 2.CO = ___________________ 3.Al 2 S 3 =___________________ 4.Copper (II) Oxide =______________

Empirical formula formula that shows the smallest whole- number MOLE ratio of the different atoms in a compound In ionic cmpds, the formula unit usually is the empirical formula

What is the empirical formula of the following molecular formulas? Ethyne, C 2 H 2 Benzene, C 6 H 6 Glucose, C 6 H 12 O 6 Acetic Acid

Ethyne, C 2 H 2 CH Benzene, C 6 H 6 CH Glucose, C 6 H 12 O 6 CH 2 O Acetic Acid CH 3 COOH = C 2 H 4 O 2 = CH 2 O

Calculation of an empirical formula Empirical formula: smallest whole-number MOLE ratio of the different atoms in a compound ∴ 1)determine moles of each element 2)determine the simplest whole # ratio of these moles

What would the formula be of a cmpd that was composed of 2 mol hydrogen and 1 mol oxygen? H:O mole ratio = 2:1 ∴ H 2 O 1 …but always written H 2 O

What would the formula be of a cmpd composed of 0.78 mol Al & 2.34 mol Br? Mole ratio of Al: Br = 0.78 : 2.34 smallest whole # ratio????? 0.78 mole Al = 1.0 Al mol Br = 3.0 Br 0.78 Al:Br = 1:3 AlBr 3

What is the empirical formula for a cmpd that contains g calcium and 1.60 g chlorine? Determine moles of Ca and Cl Determine the simplest whole # mole ratio g Ca x 1 mol Ca = mole Ca g Ca 1.60 g Cl x 1 mol Cl = mol Cl g Cl

Simplest whole-# mole ratio? mole Ca mol Cl mole Ca = 1.00 = mole mol Cl = 2.01 = mole ∴ Ca:Cl = 1:2 CaCl 2

Beaker Breaker A sample of indium chloride weighing g is found to contain g of chlorine. What is the empirical formula of the indium compound?

Determine the empirical formula in a cmpd that is 40.0% C, 6.71% H, and 53.3% O. Assume a g sample g C = 3.33 mol C 6.71 g H = 6.64 mol H 53.3 g O = 3.33 mol O 3.33 mole C/3.33 = 1.00 = mole H/3.33 = 1.99 = mol O/3.33 = 1.00 = 1 C:H:O = 1:2:1 CH 2 O

If the empirical formula is CH 2 and the molar mass is 42 g/mol, what is the molecular formula? mass of empirical formula = 14 g/mol mass of “real” formula = 42 g/mol ∴ “real” is 42/14 or 3 times heavier! C: H 1: 2 (from empirical formula) is really, 3( 1:2) = 3:6 C 3 H 6 (check: C 3 H 6 does have a mass of 42 g/mol)

If the molecular mass for the prev. problem ( cmpd that is 40.0% C, 6.71% H, and 53.3% O) is 90 g/mol, determine the molecular formula. The actual formula is how many times heavier than the empirical? 3 times ∴ molecular formula is 3xs bigger 3 (C:H:O = 1:2:1) =3:6:3 C 3 H 6 O 3

Beaker Breaker Write the symbol and oxidation # (incl +/-) for the following ions: Calcium ____________________ Chloride___________________ Oxide____________________ Sulfate____________________

Practice Complete section review on page 233 #1-5

Do Section Review p Na 2 SO 3 2.Fe 2 S 3 3.K 2 CrO 4 4.N 2 O 5 5.N 2 O 4