Aim: To calculate the empirical formula of magnesium oxide by heating magnesium ribbon in the presence of oxygen and measuring the mass change.

Materials:

1. Magnesium ribbon (approx. 5 cm)
2. Crucible with a lid
3. Tongs
4. Balance (0.001 g precision)
5. Bunsen burner
6. Heat-resistant mat
7. Retort stand
8. Ceramic triangle
9. Safety goggles
10. Lab coat
11. Gloves

Method:

1. Put on your safety goggles, lab coat, and gloves. Ensure that your work area is clear of any flammable materials.
2. Weigh the empty crucible and its lid using the balance, recording the mass to the nearest 0.001 g.
3. Cut approximately 5 cm of magnesium ribbon and weigh it using the balance. Record its mass.
4. Coil the magnesium ribbon loosely and place it in the crucible.
5. Place the crucible and its contents on the ceramic triangle, which should be set on the retort stand above the heat-resistant mat.
6. Heat the crucible with the Bunsen burner for approximately 2 minutes with the lid partially covering the crucible. This will allow a controlled flow of oxygen into the crucible and prevent the magnesium from burning too vigorously.
7. After 2 minutes, use the tongs to cover the crucible completely with the lid to cut off the supply of oxygen. Continue heating the crucible for another 3 minutes.
8. Turn off the Bunsen burner and allow the crucible to cool for about 5 minutes.
9. Carefully remove the lid and examine the contents of the crucible. If the magnesium ribbon has turned into a white powder, proceed to the next step. If not, reheat the crucible until the reaction is complete.
10. Weigh the crucible, the lid, and the magnesium oxide to the nearest 0.001 g.
11. Dispose of the magnesium oxide according to your local waste disposal regulations.

Exemplar Calculations:

1. Calculate the mass of the magnesium used in the experiment:

Mass of magnesium = (Mass of crucible + lid) + magnesium – (Mass of crucible + lid)

2. Calculate the mass of the magnesium oxide produced:

Mass of magnesium oxide = (Mass of crucible + lid) + magnesium oxide – (Mass of crucible + lid)

3. Calculate the mass of oxygen that reacted with the magnesium:

Mass of oxygen = Mass of magnesium oxide – Mass of magnesium

4. Calculate the moles of magnesium and oxygen:

• Moles of magnesium = Mass of magnesium / Molar mass of magnesium (24.31 g/mol)

• Moles of oxygen = Mass of oxygen / Molar mass of oxygen (16.00 g/mol)

5. Determine the empirical formula:

Divide the moles of magnesium and oxygen by the smallest number of moles calculated in step 4. Round the values to the nearest whole number. The empirical formula is Mg_xO_y, where x and y are the whole numbers obtained.

Safety and Environmental Concerns:

1. Wear safety goggles, lab coats, and gloves to protect against burns and exposure to chemicals.
2. Ensure that the work area is free of flammable materials, as the reaction produces a bright flame.
3. Do not look directly at the flame, as the bright light can damage your eyes.
4. Avoid inhaling fumes produced during the heating process.
5. Allow the crucible to cool before handling it, as it may be extremely hot.
6. Properly dispose of the magnesium oxide according to local waste disposal regulations.
7. Magnesium oxide is a mild irritant.

• Practical Chemistry