Question

5. As a general guideline, your experiment should look something like this: • Precisely measure the mass of an unknown Group I metal carbonate. • Dissolve in DI HO React with an ionic compound to precipitate the carbonate • Measure the mass of the NEW carbonate product and calculate the number of moles of NEW carbonate Relate the number of moles of new carbonate product to the number of moles of original carbonate product Calculate molar mass of the original Group I metal carbonate. • Deduce the identity of the original metal I carbonate. Write your own DETAILED procedure for the gravimetric analysis of a Group I metal Carbonate. (Hint: Unlike writing your procedure in a lab report, this time you ARE giving someone else instructions.)

Answer 1

Aim: To determine the identity of a group I metal carbonate

Procedure:

1. Set up a bunsen burner and place an iron ring holding the pipestem triangle above it.

2. Take an empty 15-mL clean crucible.

3. Place the crucible over the iron ring holding the pipestem triangle.

4. Heat the crucible for some time and let it cool room temperature.

3. Weigh the empty dry crucible using an analytical balance and record its weight in the data table.

4. Weigh 2 grams of unknown metal carbonate and place it in the empty dry crucible.

5. Record the mass of crucible containing unknown metal carbonate in the data table.

6. Heat the crucible containing unknown metal carbonate using earlier set bunsen burner for 2-3 minutes on a low flame.

7. Allow the metal hydrate and crucible to cool to room temperature and record its mass.  

8. Repeat the steps 6 and 7 until there is no change in the weight of unknown metal carbonate (This is done to remove any water of crystallization if present along with unknown metal carbonate).

9. Dissolve the content of crucible with approximately 200 mL deionized water in a 500 mL beaker.

10. Add 0.2 M,125 mL CaCl₂ to the beaker and stir the solution.

11. Allow the precipitate to settle down for 10 minutes.

12. Weigh Whatman filter paper No. 42 and record its mass in the data table.

13. Transfer the clear supernatant solution through Whatman filter paper No. 42 keeping the precipitate in the beaker.

14. Wash the precipitate with deionized water (10 mL at a time). Continue the washing until the precipitate is free from Cl^- ions.

15. Finally, transfer the entire precipitate from the beaker into the filter paper.

16. Slowly remove the filter paper from the funnel and place it on the watch glass. Dry the precipitate in an electric oven at 110^oC for 20-25 minutes.

17. Remove the watch containing the filter paper and precipitate and allow it to cool.

18. Weigh the filter paper and solid CaCO₃ on the analytical balance and record its weight in the data table.

19. Repeat steps 17-18 until the mass change is less than 0.005g.

20. From the mass of CaCO₃, calculate the moles of precipitated CaCO₃.

21. Calculate the molar mass and deduce the identity of the unknown metal carbonate.