(Solved): Experiment 6 Name: EMPIRICAL FORMULAS Introduction: Since molecules are made up of individual atoms ...

Experiment 6 Name: EMPIRICAL FORMULAS Introduction: Since molecules are made up of individual atoms, molecular fomulas can be written as simple ratios of atoms. Because atoms of the same element have the same mass (except for isotopic differences), all molecules of the same compound have the same fixed ratios of elements by mass The mas.s ratio of elements in a compound can be determined if the elements of the compound can be separated. Some binary compounds of a metal and nonmetal can be heated to drive oft the nonmetal as a gas. The process could be written as: $$A=B_y,a)?x{A}_{(x)}+y{B}_{(a)}$$ By weighing the compound $$(A,B$$,$$)beforeheatingandweighingtheresidue(A)$$ atter the gas $$(B)$$ is driven ott, the masses of $$\mathrm{A}$$ and $$\mathrm{B}$$ in the compound can be determined. From the masses of $$\mathrm{A}$$ and $$\mathrm{B}$$ the empirical formula can be calculated. An analogous method that is more suited to a teaching laboratory uses the same principle to determine the formula of a hydrate. The hydrate is heated to drive off the waters of hydration and leave behind the anhydrous salt. The process can be written as: Safety: - Goggles must be worn at all times. - Review the location of all fire safety equipment. - Long hair and loose clothing must be secured before beginning the experiment. Gioves are not allowed. - DO NOT TOUCH any object that could be hot. In case of an accidental burn, you should immediately immerse the affected area in cool water for several minutes and notify your instructor. - The hydrates used in this experiment should not be ingested or inhaled. - Dispose of the anhydrous compound (the residue) in the provided waste container. PROCEDURE: WORK ALONE NOTE: if you spill the residue, drop your crucible, etc. you may have to start overl Be careful and be considerate of those around you. If you cause someone else to have an accident through carelessness you will lose points. LET THE CRUCIBLE COOL AS DIRECTED - A HOT CRUCIBLE WILL NOT GIVE AN ACCURATE MASS. 1. Check the crucible (with lid) for cracks (notify your instructor if you find cracks). Place the crucibie (with the lid) in the triangle over the Tirrill burner flame. Heat this for two minutes 2. Allow the crucible and lid to cool for at least 5 minutes: 3. Weigh the empty crucible (with lid) on an analytical balance and record the mass on line 1. Weigh the fid separately (ust in case it gets broken during the experiment) and record this mass on line 6 . 4. Add al of the hydrate powder to the crucible, weigh it (with the lid). and record the total mass on line 2. 5. Place the crucible (with the lid) in the triangle over the Tirrill burner flame. Keeping the lid slightly open is recommended. Apply full heat to make the bottom of the crucible red hot for 15 minutes 6. Allow the crucible with residue and lid to cool (for at least $$5\min$$ ), then weigh it and record the mass on line 3 . 7. Heat the crucible with residue and lid to red hot for 5 minutes. Cool for at least 5 minutes, weigh again, and record the mass on line 4. 8. Check with your instructor to determine whether a third heating may be needed. 9. Dispose of the residue in the provided container and return the unknown tube to your instructor. 10. Be sure to staple the data slip provided by your instructor (for probiem \#6) to your lab repoct. 2. Use the data and caiculabions above to determine the percent MgSO. (by mass) in the hydrate (starting compound): 3. Use the data and calculations above to detemine the percent water (by mass) in the hydrate (starting compound). 4. How many $$\mathrm{kg}$$ of your unknown would contain $$845\mathrm{g}$$ of water? Use the appropriate mass percentage you caiculated above and use dimensional analysis: C. Determine the simplest mole ratio to find the empirical formula: (Note: round to the nearest whole number for the moles of water in the hydrate) Formula of the hydrate: MgSO. $${\mathrm{H}}_2\mathrm{O}$$ 6. Hydrate H2: Data for hydrate in2 (supplied on the data slip) Mass of hydrate before heating Mass of residue after heating (= anhydrous compound) Loss of mass upon heating (=water) A. Calculate moles of the anhydrous compound $$\left({\mathrm{MgSO}}_4\right)$$ : B. Calculate moles of water: C. Determine the simplest mole ratio to find the empirical formula: Formula of the hydrate: MgSO. Ho D. Cafculate the percentage water (by mass) and percentage $${\mathrm{MgSO}}_4$$ (by mass) in this hydrate: