Chemguide

Extra material needed for the 2010 exam - Chapter 17

This page lists the material from the old Edexcel syllabus which isn't covered by my new Edexcel IGCSE Chemistry book. The extra material will just follow on from the end of the chapter.

Some iron chemistry

You have to be able to describe the action of steam, hydrogen chloride and chlorine on iron.

Iron and steam

This is covered in chapter 7 at the bottom of page 65.

Iron and hydrogen chloride

We are talking here about hydrogen chloride gas - not its solution in water, hydrochloric acid. If dry hydrogen chloride gas is passed over heated iron wool, it reacts to give off-white iron(II) chloride and hydrogen.

If you were using hydrochloric acid, the iron reacts to give a very pale green solution of iron(II) chloride and hydrogen gas.

You normally see solid iron(II) chloride as pale green crystals. The colour is caused by the presence of the water of crystallisation. If you pass dry hydrogen chloride gas over hot iron, there is no water present, and you get anhydrous iron(II) chloride which is off-white. (If you aren't sure about this, there is more about water of crystallisation on pages 83-84.)

Iron and chlorine

If you pass dry chlorine over heated iron wool, it burns brightly and produces iron(III) chloride. If everything is perfectly dry, this forms black crystals. If there is even a trace of water present, it forms a solid which is various shades of reddish brown.

You will find a short bit of video on YouTube showing hot iron powder reacting with chlorine in an open flask. This gives a good impression of the various reddish-brown colours you get if there is any moisture present - in this case, water vapour in the air. However, it doesn't show the iron burning or the formation of the black crystals.

The changes from iron to iron(II) chloride or iron(III) chloride are both oxidation. Chlorine is a powerful oxidising agent, and can oxidise the iron all the way to iron(III) chloride.

You can think of this (although it isn't strictly accurate), as oxidation by electron loss to give compounds containing iron(II) or iron(III) ions. The proper explanation has to wait for a higher level.

The electrolytic purification of copper

You don't have to know how copper is produced from its ore, but you do have to know the last stage of this process where impure copper is purified using electrolysis.

The impure copper is made into the anode during the electrolysis of copper(II) sulfate solution. In all the cases you will find in the electrolysis chapter in the book, the anode has been an inert material like carbon or platinum. However, it is possible with some metal anodes for the anode itself to get involved in the electrolysis. That is happening here.

You will find this process described in detail on a page about the extraction of copper elsewhere on this site. You don't need to read all of the page - look for "Electrolytic refining" in the purification of copper section about two-thirds of the way down.

The extraction of zinc

You have to know about the extraction of zinc by electrolysis (the main method) and by the reduction of zinc oxide by carbon monoxide.

This has only been asked as a small part of a question in the eight exams (including the specimen paper) from May 2005 to May 2008. Because there is no point in reinventing wheels, I will pass you over to a page on Doctor Phil Brown's fact-filled site. You will find the zinc extraction about 3/4 of the way down the page. The copper purification is covered on that same page if you want a GCSE rather than an A level view of it (as on Chemguide).

If you want another view of any of the GCSE material, Phil Brown's site is always worth looking at.

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