Ferrites were invented by Yogoro Kato and Takeshi Takei in Japan in 1930. They are magnetic mixed ox — Physical Chemistry — Thermodynamics Chemistry Question

Ferrites were invented by Yogoro Kato and Takeshi Takei in Japan in 1930. They are magnetic mixed oxides of iron and divalent metals (M) expressed as MFe₂O₄. A representative example of ferrites is Fe₃O₄, where M²⁺ = Fe²⁺, and many divalent cations can form ferrites with Fe³⁺ cations. Today, ferrites are very important magnetic materials used in electronics.

Ferrites are also important in waste water treatment, where they are used for the removal of heavy metal cations. This is related to the synthetic process of ferrites. Ferrites can easily be prepared by a wet precipitation technique from a solution containing M²⁺ and iron (Fe²⁺ and/or Fe³⁺) cations under oxidative conditions and with a controlled pH and temperature. In this experiment, you will prepare a ferrite, ZnFe₂O₄, from a solution of Zn²⁺ and Fe²⁺.

Reaction: Zn²⁺, Fe²⁺ -[Ox]-> (Zn_x^II Fe_{1-x}^II) Fe_2^III O_4

Chemicals
* acetic acid–sodium acetate buffer solution (pH 4)
* iron(II) sulfate heptahydrate (FeSO₄ · 7 H₂O)
* sodium hydroxide solution, (c = 2 mol dm^-3)
* zinc sulphate heptahydrate (ZnSO₄ · 7 H₂O)

Apparatuses and glassware
* air pump (flow rate 100 cm₃ min^-1) and tubing
* Büchner funnel
* Erlenmeyer flask (200 cm₃)
* glass microfiber filter (to capture particles of ca. 0.3 µm)
* graduated pipette (2 cm₃)
* hot-plate magnetic stirrer
* magnet
* pH test paper (effective for pH 7–11)
* stirring bar
* thermometer
* suction flask
* tweezers

Procedures
(1) Assemble the experimental setup as shown in Fig. 37.1. [VISUAL]
(2) Dissolve FeSO4·7 H₂O (2.0 g) in water (40 cm₃) in the Erlenmeyer flask.
(3) Start stirring the solution.
(4) Dissolve ZnSO4·7 H₂O (0.20 g) in the solution.
(5) Start air bubbling through the glass tube (see Fig. 37.1).
(6) Heat the solution until the temperature reaches 65 – 75 °C. Add around 6 cm₃ of the sodium hydroxide solution and confirm that the solution pH reaches 9 – 11. If not, add more of the solution until the pH has reached 9 – 11. The time when the pH is adjusted is the reaction start time.
(7) Add the sodium hydroxide solution at appropriate intervals to maintain the pH at 9– 11 while maintaining the solution’s temperature. The color of the precipitate will gradually turn deep black.
(8) One hour after the start of the reaction, stop stirring, air bubbling, and heating.
(9) Place the magnet on the outer wall of the flask and confirm that the magnet attracts the precipitate.
(10) Separate the precipitate by suction filtration using a glass microfiber filter. Recover the precipitate appropriately (it may be difficult to recover the fine particles that stick to the flask wall).
(11) Wash the precipitate with the acetate buffer (50 cm₃).
(12) Wash the precipitate with water, and then dry it at around 80 °C in an air oven.
(13) Weigh the precipitate.

Fig. 37.1 Experimental setup.