1. Determination of the Percent Composition of an Unknown Mixture. Gravimetric analysis of a sodium chloride and sodium hydrogen carbonate mixture.

2. Purpose To experimentally determine the percent composition of a mixture of sodium chloride (table salt) and sodium hydrogen carbonate (baking soda).

3. Concept Gravimetric analysis is the process of using mass and difference in mass to quantitatively analyze a substance. (Application is left to the student)

4. Safety Name HFRSpecial Sodium Chloride 100None Sodium Hydrogen Carbonate 000None

5. Procedure.1 Obtain and mass a clean dry test tube and record. Add approximately 1 gram of the unknown mixture to the test tube.

6. Procedure.2 Mass the test tube and unknown and record. Set up and clamp the test tube as shown and begin gently heating the unknown mixture for 3 - 4 minutes.

7. Procedure.3 Heat the mixture strongly for 15 min with occasional turnings. Be sure than no solid material is ejected from the test tube. Let the test tube and mixture cool. You may notice some crazing of the glass

8. Procedure.4 Determine the final mass. Mass the test tube and mixture and record the intermediate mass. Repeat the strong heating for an additional 10 minutes then let the test tube cool. Re-mass the test tube and mixture and record the intermediate mass. Repeat the heating until the intermediate masses are consistent. This is to be sure that the reaction is complete.

9. Procedure.5 Clean up. Dispose of the test tube in the broken glass receptacle. Return the equipment. Begin the analysis and calculations.

10. Analysis Determine what happens to each of the components of the mixture as it is heated. NaCl  ? NaHCO 3  ? Is there a reaction? (Write it out) What left the test tube? How can that information be used to determine the percent composition of the mixture?

11. Calculations Determine the percentage of NaCl and NaHCO 3 in the original mixture. Determine the mass of NaHCO 3 in the original mixture Determine the mass of NaCl in the original mixture. Determine the percentage of each

12. Conclusion Summarize the procedures Give the results List sources of error Describe an error propagation