ELECTROLYSIS Flashcards
What is electrolysis?
Breaking down using electricity. You use an electric current to break down an ionic compound. The compound that is broken down by electrolysis is called the electrolyte.
What is the positive electrode called?
The anode
What is the negative electrode called?
The cathode.
What are the electrodes often made of?
An unreactive (or inert) substance, such as graphite or sometimes expensive platinum metal. This is so the electrodes do not react with the electrolyte or the products made in electrolysis.
What happens when the ions reach the electrodes?
They lose their charge and becomes elements. At the electrodes gases may be given off, or metals deposited. This depends on the compound used and whether it is molten or dissolved in water.
What happens when electrolysing ionic compounds in solution? (aqueous) (at the cathode)
It is more difficult to predict what will form. This is because the water also forms ions, so the products that reach the electrodes may be unexpected.
In electrolysis, only metals of very low reactivity, below hydrogen in the reactivity series, are deposited from their aqueous solutions.
The less reactive element will usually be formed.
In aqueous solutions, there will usually be positively charged metal ions and H+ ions from water, which are attracted to the cathode.
When might electrolysis be used on covalent compounds?
If they react (or ionise) in water to form ions.
What is gaining electrons called?
Reduction.
What is losing electrons called?
Oxidation.
What happens at the anode during the electrolysis of aqueous solutions?
Hydroxide ions are usually discharged, so you see oxygen gas given off.
This happens unless the solution contains a reasonably high concentration of a halide (group 7 ion), such as Cl-. In this case, the halide ion is discharged and the halide ion is formed.
What ore do you get aluminium oxide from?
bauxite. The ore is mined by open cast mining, digging it directly from the surface. Mauxite contains mainly aluminium oxide, however, it s mixed with other rocky impurities, so the first step is to seperate aluminium oxide from the ore. The impurities contain a lot of iron (III) oxide. This makes the waste solution from the separation process a rusty brown colour. The brown waste water has to be stored in large lagoons.
How do scientists reduce the melting point of magnesium oxide?
They mix the magnesium oxide with molten cryolite . The large amount of electrical energy that is transferred to the electrolysis cells keeps the mixture molten.
During the electrolysis of magnesium oxide, what is formed where?
Aluminium forms at the negative electrode (cathode).
Oxygen is produced at the positive electrode (anode).
The oxygen reacts with the hot carbon anode, making carbon dioxide gas. So the carbon anode gradually burns away and needs to be replaced regularly.
