Making salts on a micro-scale in a high school chemistry laboratory has the advantages of being quick, simple and easy to prepare. For example, here is an experiment we recently carried out making magnesium sulfate in an IGCSE Chemistry class.
A two decimal place electronic balance, tweezers and a 0.2ml (200 microlitre) automatic pipette were used in addition to the materials shown above.
1. Cut out a 10cm x 10cm plastic sheet (from an A4 plastic wallet) and record its mass on an electronic balance.
2. Place 0.2ml of 1M sulfuric acid on the centre of the sheet.
3. Take a 4 cm length of magnesium ribbon and bend it into an oval shape which can be placed around the globule of acid.
4. Place the magnesium around the acid.
5. When the bubbling has stopped, pick up the magnesium with a pair of tweezers and rinse off with a small volume of distilled water.
6. Place the plastic sheet in a suitable place, such as a sunny windowsill or a low temperature drying cabinet, to allow the water to evaporate and the salt to crystallise.
7. Weigh the plastic sheet + the solid using an electronic balance and determine the mass of product formed.
8. If time allows, break up the crystals with a spatula and dry further using warm air from a hair dryer until a constant mass is obtained.
Calculations can be performed to determine the percentage yield of magnesium sulfate (presumably the heptahydrate) made.
The plastic sheets can be washed and re-used.
Thanks to Bob Worley for inspiring us to try out this and other high school chemistry lab experiments on a microscale. Here is a link to Bob’s Microchemuk website which is a goldmine of resources and ideas.