Lab Experiment: Differentiating Carbonate and Hydrogen Carbonate Salts, Identifying Sodium, Lecture notes of Stoichiometry

Download Lab Experiment: Differentiating Carbonate and Hydrogen Carbonate Salts, Identifying Sodium and more Lecture notes Stoichiometry in PDF only on Docsity! experiment date(s): Page 1 of 2 Experiment 5 – Compound Identity by Mass Relationships Goal: To illustrate the utility of chemical formula and reaction stoichiometry. Discussion: You will have one of the following 4 compounds as an unknown, and must determine its identity. The first two are referred to as hydrogen carbonate salts because they contain the hydrogen carbonate ion, HCO3 -. The second two are carbonate salts because they contain the carbonate ion, CO3 2-. NaHCO3 KHCO3 Na2CO3 K2CO3 There are two experimental procedures used to distinguish between the four compounds. 1. Distinguish between carbonate and hydrogen carbonate Experiment: Heat the solid. If the compound is a carbonate, nothing much happens. At most, the sample will lose between 0.01 and 0.04 grams of mass. If you have a hydrogen carbonate, it will lose a significant amount of mass, usually greater than 0.1 grams. In the equations below, M = metal = Na or K. Carbonate: M2CO3 (s) __heat___> M2CO3 (s) (no change) Hydrogen carbonate: 2 MHCO3 (s) __heat___> M2CO3 (s) + H2O (g) + CO2 (g) (mass is lost when gases escape) Once it is determined whether the compound is a carbonate or hydrogen carbonate, then it is time to determine whether the metal is sodium or potassium. 2. Distinguish between sodium and potassium salts Experiment: Convert the solid to a chloride salt by reaction with HCl. The mass ratio of chloride salt to original compound is different for Na vs. K. (a) If the compound is a carbonate, then the equation for conversion to the chloride salt is as follows: M2CO3 (s) + 2 HCl (aq) _____> 2 MCl (s) + H2O (g) + CO2 (g) Notice that for every one mole of carbonate salt reacting, two moles of chloride salt are produced. To determine the theoretical mass ratio, start with any mass of the original compound (the example starts with 1.00 g) and calculate the mass of product expected. The example below is for sodium carbonate. You may need to perform this same calculation for potassium carbonate.