Falando pelos Cotovelos

Add 4.0 mL of 1M FeCl₃ and 1.0 mL of 2M FeCl₂ solution to a 100 mL beaker. Add a magnetic stirring bar and begin stirring.

Continue stirring throughout the slow addition over a period of 5 minutes of 50 mL of 1.0 M aqueous NH₃ solution. After an initial brown precipitate, a black precipitate will form (magnetite). One way to accomplish a slow addition is to drip the ammonia solution from a buret or separatory funnel or by using a dropper to transfer the solution. CAUTION: Although 1 M NH₃ is fairly dilute, NH₃ is a strong base.

Turn off the stirrer and immediately use a strong magnet to work the stir bar up the walls of the beaker. Remove the stir bar with tongs or a gloved hand before it touches the magnet.

Let the magnetite settle, then decant (pour off) and discard the clear liquid without losing a substantial amount of solid. You can speed the settling process by putting a magnet under the container.

Transfer the solid to a weighing boat with the aid of a few squirts from a wash bottle.

Use a strong magnet to attract the ferrofluid to the bottom of the weighing boat. Pour off and discard as much clear liquid as possible. Rinse again with water from a wash bottle and discard the rinse as before. Repeat the rinsing a third time.

Add 1-2 mL of 25% tetramethylammonium hydroxide. Gently stir with a glass rod for at least a minute to suspend the solid in the liquid. Use a strong magnet to attract the ferrofluid to the bottom of the weighing boat. Pour off and discard the dark liquid. Move the strong magnet around and again pour off any liquid. If the ferrofluid does not spike, continue to move the strong magnet around, pouring off any liquid.

What happens when you move a magnet under the ferrofluid?