GCSE OCR Gateway Chemistry C3.4a–b Electrolysis (1)

New OCR Gateway specification from September 2016 Higher tier: grades 9 to 4: 

In this and subsequent posts I’m simply going to explain and illustrate each learning objective as they come up in the topics in the new GCSE specification. 

I’m giving you my notes from each lesson.

You can really get ahead of your class if you follow this blog and all the posts that will appear here about the new GCSEs over the coming months. 

This rejigging of the specification is just that: there is nothing really new here it has all been with us for the past half century at least. 

That written in italics is for the higher tier paper only.

C3: Chemical Reactions

C3.4 Electrolysis (1)

C3.4a recall that metals (or hydrogen) are formed at the cathode and non-metals are formed at the anode in electrolysis using inert electrodes and to recall the terms cations and anions.

Electrolysis is the conduction of electricity by a compound in its molten or aqueous state with decomposition into its elements at the electrodes.

Electrolysis takes place in an electrolysis cell.

Electrolysis occurs only in a molten or aqueous liquid called an electrolyte.

All electrolytes conduct electricity using ions not electrons.

Two electrodes are needed to carry the electricity into the electrolyte.

The anode is positively charged and the cathode is negatively charged.

Inert electrodes are electrodes that do not get involved in the chemical changes at the electrodes.

In electrolysis, positive ions are attracted to the negative cathode so positive ions are called cations.

Also negative ions are attracted to the positive anode and so they are called anions.

The set up looks something like this in the diagram below:

There are several patterns to electrolysis using inert electrodes.

a)  metals are always given off at the cathode

b)  hydrogen is always evolved at the cathode

c)   non–metals are given off at the anode.

C3.4b predict the products of electrolysis of binary ionic compounds in the molten state

The patterns above will help predict the products of binary compound electrolysis.

Compound	Anode product (+)	Cathode product(—)
Water (H2O)	oxygen	hydrogen
Sodium chloride (NaCl)	chlorine	sodium
Lead bromide (PbBr2)	bromine	lead
Zinc chloride (ZnCl2)	chlorine	zinc
Aluminium oxide (Al2O3)	oxygen	aluminium