Skip to main contentText Only version of this page
bbc.co.uk
Home
TV
Radio
Talk
Schools
A-Z Index

SATURDAY
12th March 2005
Text only
Schools GCSE Bitesize Revision
Chemistry  useful products from rocks

BBC Homepage
Home

SOS Teacher

Message Boards

TV

Other Sites

Site Guide

Credits

About the BBC

Contact Us

Help


Like this page?
Send it to a friend!

 

 
Home / Chemistry / Useful products from rocks / Chemicals from salt

Hot Links

Elementary!
Test your knowledge of the Periodic Table ..

Onion Street

Post ideas and check out Science messages here.

The chlor-alkali industry

You need to know the products formed by the electrolysis of concentrated sodium chloride solution, and simple laboratory tests for them.

The electrolysis of brine
Brine is concentrated sodium chloride solution. If an electric current is passed through it, hydrogen gas forms at the negative electrode and chlorine gas forms at the positive electrode. A solution of sodium hydroxide forms. These three products have important uses in industry.

You might have expected sodium metal to be deposited at the negative electrode. But sodium is too reactive for this to happen, so hydrogen is given off instead.

image: electrolysis of sodium chloride solution


Laboratory tests
The table shows the common laboratory tests for the products from the electrolysis of brine.

Substance Test and result
hydrogen gas a lighted splint pops
chlorine gas damp litmus paper is bleached white
sodium hydroxide solution universal indicator solution turns purple
|
http://www.bbc.co.uk/gcsebitesize Intro 1 2 3 Print
sterilize
To sterilize means to make something free from micro-organisms such as bacteria.
electrolysis
Electrolysis is the decomposition (separation or break-down) of a compound using an electric current.
product
A product is a substance formed in a chemical reaction.
electrode
Electrodes are conductors used to establish electrical contact with a circuit. The electrode attached to the negative terminal of a battery is called a negative electrode, or cathode. The electrode attached to the positive terminal of a battery is the positive electrode, or anode.
catalyst
A catalyst changes the rate of a chemical reaction without being changed by the reaction itself.


Terms of Use | Privacy & Cookies Policy