Empirical formulas of compounds – experiment part a

Objectives To Determine the Empirical Formula for Magnesium Oxide. To Gain Practical Experience in Developing Techniques Using a Crucible.

Discussion This experiment will spark interest in the reactions of metals as they combined with oxygen gas in the air. Magnesium is the metal from group two family for this investigation. Mass of metal is measured before reaction and the mass of oxide is measured after the reaction to determine the formula of metal oxide.

discussion Sample Problem 1: Determining an Empirical Formula A 0.279-g sample of iron is heated and allowed to react with oxygen from the air. If the product has a mass of 0.400 g, what is the empirical formula of the iron oxide?

discussion Solution to sample problem: 0.279 g Fe X 1 mole Fe/55.85 g Fe = 0.00500 Fe The mass oxygen that reacted is 0.400 g product – 0.279 g iron = 0.121 g. 0.121 g O X 1 mole O/16.00 g O = 0.00756 mole O Fe 0.00500/0.00500 O 0.00756/0.00500 = Fe l.00 O1.51 Double mole ratio we get Fe2O3 and stock system is iron (III) oxide.

Equipment Clay triangle Crucible Tongs Crucible and Cover

chemical Magnesium, Mg Ribbon

procedure Empirical Formula of Magnesium Oxide 1. Support a crucible and cover with a clay triangle, and place on a ring stand. Fire the crucible and cover to red heat using the tip of the flame from a laboratory burner. 2. Turn off the burner, and allow the crucible and cover to cool for 10 minutes. Weigh the crucible and cover on a balance.

Procedure 3. Cut a 25-cm strip of magnesium ribbon, and roll the metal into a flat coil. Place the coil of magnesium in the crucible so that it lies flat against the bottom. Reweigh the crucible, cover, and magnesium metal. 4. Return the crucible to the clay triangle. With the cover off, fire the crucible to red heat. When the magnesium sparks and begins to smoke, immediately remove the burner and place the cover on the crucible using crucible tongs.

procedure 5. After the smoke has ceased, continue to heat the crucible and cover until the metal is completely converted to a gray-white residue. The progress of the reaction can be checked periodically by removing the burner and raising the cover with the crucible tongs. 6. When the metal no longer sparks, turn off the burner and allow the crucible to cool for 10 minutes. Using a dropper pipet, and drops of distilled water until no fizzing is observed from the gray-white residue.

Procedure 7. Cover the crucible, and heat for 5 minutes. Turn off the burner, and allow the crucible to cool for 10 minutes. Weigh the crucible and cover containing the magnesium oxide. 8. Clean the crucible, and repeat the procedure. 9. Calculate the empirical formula for each trial.