We saw earlier in discussions about functional groups that chemists can subtly change the properties of molecules by unscrewing a functional group here and replacing another one there. Altering the structure and hence the properties of a an important evolutionary molecule such as adrenaline can lead to drugs like amphetamine, methamphetamine and MDMA. (Can you spot the error in the video?)
Chemists involved in developing new polymers take a similar approach. Ethene under the influence of pressure and catalyst can polymerise to form polythene. Polythene has many desirable properties but also one major drawback, it can’t be manufactured with colour.
If one of the hydrogen atoms in ethene is replaced with a chlorine atom the molecule chlorethene results. (vinyl chloride). When this molecule undergoes addition polymerisation the plastic polyvinyl chloride or PVC is produced. The addition of chlorine atoms into the long polymer chain results in a substance that can be manufactured in a variety of bright colours.
Poly vinyl chloride was dicovered twice in the nineteenth century. It was in the 60’s however that PVC became popular as a material that could be used to make fashionable clothes. After the austere years following the second world war the public demanded bright fashions and new music to go with them. The Austin Powers movies are a clever parody of the sixties and catch the colour of the times well.
How many pieces of shiny bright coloured clothing can you find in the clip from the Austin Powers movie?
Alkenes and addition polymerisation, writing equations
NCEA questions often ask you to show what the polymer chain would look like if three monomer units are combined. You can also be asked to draw the structural formula of the monomer that produced a polymer
…….and the students in the next video are successfully studying sixth form chemistry. If they can do it so can you……..its OK to be a chemistry geek!
Look at the three videos of the reactive metals sodium and calcium when small pieces are dropped into water. Observations allow us to work out what is happening and develop a general word equation for the reactions.
Some stuff for experts:
sodium dissolves in water. A new compound must be formed in the solution.
calcium dissolves in water. Another compound must be formed in solution
What could this compound be? Acidic solutions contain lots of hydrogen ions. Basic solutions contain lots of hydroxide ions.
Phenolphthalein indicator turns from colourless to pink when it is in a basic solution. When phenolphtalein turns pink there are hydroxide ions present.
As the metals dissolve in water hydroxide ions are produced
When sodium dissolves in water sodium hydroxide is formed in solution.
When calcium dissolves in water calcium hydroxide is formed.
A gas is given off which pops when lit
When sodium and calcium dissolve in water hydrogen gas is formed
If you have followed all of that well done, if not don’t worry. For achievement in level 1 chemistry you simply have to remember the word equations and use them.
reactive metal + water —–> metal hydroxide + hydrogen
Sodium + water —–> sodium hydroxide + hydrogen
Calcium + water —–> calcium hydroxide + hydrogen
For merit and excellence you need to be able to write underneath the word equation the chemical formulae and then balance. See the exercises in your workbook.
Leave any questions you want answered by clicking on the response link. Good luck
Lithium sodium and potassium tarnish quickly in air when the protective oil coating is wiped of. They are extremely reactive metals. Reactive metals get coated in a layer of metal oxide when they are left exposed to air long enough
Magnesium is another very reactive metal particularlyl when its oxide layer is is scraped off. The flame is difficult to extinguish and the metal has been used as the casing for incendiary shells. ( the casing will explode if you try and put the fire out with water)
…….and finally even iron can burst into flames. The iron has to be in the form of iron wool ( it won’t work with an iron nail for instance….why not?). It has to be heated and will only burn in an atmosphere of pure oxygen. Can you remember how to make oxygen gas and how to test for it?
Finally word equations. Word equations are a kind of chemical shorthand to stop you writing heaps of words. For instance if we were to summarise all of this stuff we might write a sentence like…
Metals tarnish in air. The oxygen in the air will chemically combine with the atoms of the metal to form a new compound The compound formed when a metal reacts with oxygen is called a metal oxide.
And the word equation:
reactive metal + oxygen —–> metal oxide
Being able to write to basic word equations will help you with achievement question.
The next two steps will help you achieve merit and excellence. For instance if we complete the process for magnesium burning in oxygen
1.general word equation: Reactive metal+oxygen—–>metal oxide
