 # SURVEY OF CHEMISTRY LABORATORY I CHEM 1151 L

• Slides: 15 SURVEY OF CHEMISTRY LABORATORY I CHEM 1151 L EMPIRICAL FORMULA OF ZINC CHLORIDE CAUTION!!! BE SURE TO WEAR SAFETY GLASSES AT ALL TIMES IN THE LABORATORY NO EXCEPTIONS TO THIS RULE! EMPIRICAL FORMULA OF ZINC CHLORIDE Students will determine - the empirical formula of zinc chloride by a process known as synthesis - the empirical formula from their data - the empirical formula from the class average It is best to perform several experiments and obtain average values for the result EMPIRICAL FORMULA - The lowest whole number ratio of atoms present in a compound - the lowest whole number ratio of moles of atoms in a compound For example - The molecular formula of glucose is C 6 H 12 O 6 - The empirical formula is CH 2 O EMPIRICAL FORMULA Can be determined by the following methods Analysis - A compound is broken down into its element - The mount of each element present is accurately determined Synthesis - Prepared from accurately measured amounts of each of its elements EMPIRICAL FORMULA - Determine the mass of each element found in the formula (may be grams or percentage composition by mass) - Convert each mass to moles using the atomic masses of the appropriate elements - Divide each mole amount by the smallest number of moles - Round each mole ratio to the nearest integer - Write the whole numbers as subscripts in the formula EMPIRICAL FORMULA Determine the empirical formula of a compound whose composition is determined to be 74. 83% carbon and 25. 17% hydrogen Assume 100. 0 g sample % of each element equals grams C H 1. 000 ≈ 1 4. 007 ≈ 4 Empirical Formula: CH 4 ZINC METAL - Mass about 1 gram of zinc metal - Record this mass EVAPORATING DISH - Mass a clean, dry evaporating dish - Record this mass HYCHLORIC ACID - Use the automatic dispensing bottle - Dispense 10 m. L of 12 M hydrochloric acid (HCl) directly into the evaporating dish HYCHLORIC ACID + ZINC METAL - Carefully add the zinc to the dish containing the HCl - Must be done in the hood - Allow all of the zinc to dissolve EVAPORATE LIQUID - Gently warm solution on a hotplate - Must be done in the hood - Avoid spattering - A white powdery substance (zinc chloride) will form COOL AND MASS PRODUCT - Avoid melting of zinc chloride - Take the dish off the hotplate when content is dried enough - Allow the dish to cool COOL AND MASS PRODUCT - Mass the dish and the zinc chloride - Record the mass CALCULATIONS - Complete your calculations on the data sheet - Report the percent by mass of each element to the instructor before leaving the lab - The class average is needed to complete the lab report