Theory behind this practical:
You need to learn the order of the reactivity series. Rather than simply looking at a list and trying to memorise it, it is very useful to see them in action and compare reactiveness. You will be able to judge where a new metal will fit.
To begin with, demonstrate to the class that the reactions of Li, Na and K with water. At the same time, have the “unmade” reactivity series on the board:
When these have been put in order put a piece of calcium in a boiling tube of water and some magnesium in another one. The calcium will merrily fizz but the magnesium will do nothing. Calcium can then sit underneath lithium on the board. Now put magnesium and zinc in a boiling tube each part filled with hydrochloric acid. The magnesium reacts much more vigorously than the zinc so they too can be placed on the board
Next, put into fresh boiling tubes of hydrochloric acid, copper and iron. Show that these cannot be seen to react at all, even with acids. I now get the students to apply their knowledge to decide which of these is most reactive. If they struggle to get there, remind them of rusting cars. bikes and outdoor structures. Then remind them that their drinking water arrives through copper pipes and if it reacted, you would be drinking what came out.
Finally, gold – even if you dipped gold leaf into the acid, you cannot see the reactivity differences from the above. Remind them that there are Egyptian artefacts made from gold that are still as lustrous and when made 4000 years ago.
Final task. Drop a piece of Ba into water and ask them to position it into the order that they have made. Make the students justify their choice.
- Small samples of Li, Na, K, Ba in oil
- Small pieces of Zn, Mg ribbon, Ca
- Iron nail, copper sheet
- Boiling tubes (4)
- HCl(aq) 2moldm-3
- Large glass bowl for alkali metals
- Safety screen
- Filter paper (2)
- Universal indicator or phenolphthalein (if requested)
Usual lab rules must be adhered to:
- Students sitting or standing a safe distance back (alkali metals can spit).
- All students and staff wearing goggles
- Water can be come alkaline, do not touch
- Good ventilation needed (metal hydroxides in vapour irritate lungs)
For further/more detailed information, check all reagents and practices at CLEAPSS.