Science Infoblog

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

2. word equation: magnesium + oxygen —–> magnesium oxide

3. inserting chemical formulae: Mg + O₂ —–> MgO

4. fully balanced equation: 2 Mg + O₂ —–> 2 MgO

Tags: chemistry, metals

This entry was posted on Monday, March 23rd, 2009 at 10:11 pm and is filed under NCEA Level 1 Chemistry, Year 11 Science Posts. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.