The Empirical Formula of a Binary Compound Chemical

The Empirical Formula of a Binary Compound

Chemical Formulas § § § Indicate compound composition Format: § Chemical symbols for elements § Subscripts to indicate # atoms Example: § Carbon dioxide § 1 C atom and 2 O atoms: CO 2

Empirical vs. Molecular Formulas § Empirical Formula § § Simplest formula Determined using mass ratios (from experiment) Gives relative ratio of the elements in a compound Subscripts smallest integers possible (e. g. ) CH 2 O § Molecular Formula § § § Includes actual numbers of each atom present Total mass can be found by summing masses of atoms in the formula (if known) will be an integer multiple of the empirical formula (e. g. ) C 4 H 8 O 4

Steps for Determining an Empirical Formula 1. 2. 3. 4. Determine the relative mass of each element in the formula in grams. Covert grams to moles to get molar ratios. Divide moles by smallest mole amount. § Multiply if necessary to get round number. Use molar ratios as subscripts in formula.

Empirical Formula Example 0. 460 g of Na were reacted with S to produce 0. 781 g of sodium sulfide. What is the empirical formula of the product? Step 1: Find grams of each element 0. 781 g of Nax. Sy, where x and y are unknown subscripts 0. 781 g – 0. 460 g Na = 0. 321 g S Step 2: Convert grams to moles using molar masses 0. 460 g Na x (1 mol / 22. 99 g) = 0. 0200 mol Na 0. 321 g S x (1 mol / 32. 07 g) = 0. 0100 mol S

Example Continued Step 3: Divide by smaller number of moles 0. 0200 mol Na / 0. 0100 = 2 0. 0100 mol S / 0. 0100 = 1 Step 4: Use resulting ratios as subscripts in formula Empirical formula is Na 2 S.

Copper Chloride – which one? § § In ionic compounds, copper exists (usually) in one of its two ionic forms (Cu+ or Cu+2) Two common forms of copper chloride are known: § Copper (I) chloride, Cu. Cl § A. k. a. cuprous chloride § White solid § Copper (II) chloride, Cu. Cl 2 § A. ka. cupric chloride § Brown solid

Determining the Formula n n n Reaction of zinc with the copper ions in solution will produce solid copper metal This is a single displacement reaction Cu. Clx + y Zn(s) Zny. Clx + Cu(s) The mass of chloride can be found by difference from the known mass of copper chloride used.

Determining the formula n Convert the mass of copper and the mass of chlorine into mole units q q n Find the mole ratio q n molar mass of copper (Cu) = 63. 546 gmol-1 molar mass of chlorine(Cl) = 35. 453 gmol-1 normally we divide the larger number of moles by the smaller Express in the smallest whole number ratio