Electrolysis Notes

During the electrolysis of aluminum, oxygen reacts with the positive carbon electrodes to produce carbon dioxide ( $CO_2$ ).
At high temperatures, oxygen reacts with the carbon electrode to produce carbon dioxide ( $CO_2$ ), causing the electrode to wear away.
Aluminum oxide and cryolite are involved in the electrolysis of aluminum.

An electrolyte is a solution that conducts electricity.
Electrolysis is used to extract some metals because the metal is too reactive to be extracted using carbon.
Electrolysis of a molten ionic compound.

In molten sodium chloride, the ions produced are sodium ( $Na^+$ ) and chloride ( $Cl^-$ ).
In aqueous sodium chloride, the ions produced are sodium ( $Na^+$ ), chloride ( $Cl^-$ ), hydrogen ( $H^+$ ), and hydroxide ( $OH^-$ ).
In a solution (aqueous), water molecules break down to produce hydrogen ( $H^+$ ) and hydroxide ( $OH^-$ ) ions.

In an aqueous ionic compound, the ion attracted to the cathode is either the hydrogen ion ( $H^+$ ) or the metal ion ( $M^n$ ) (e.g., $Na^+$ ).
- If the metal is less reactive than hydrogen, it will gain electrons and form a neutral element.
In an aqueous ionic compound, the ion attracted to the anode is either a halide ion (Group 7) or hydroxide ( $OH^-$ ).
- If a halide ion is present, it will lose electrons and form a neutral element.
- If a halide ion is not present, hydroxide ( $OH^-$ ) will lose electrons to form oxygen ( $O<em>2$ ) and water ( $H</em>2O$ ).

Magnesium chloride ( $MgCl_2$ ) must be molten or dissolved in water to be electrolyzed because ions need to be able to move to the electrodes and carry charge.