Determine mass of water in hydrated crystals

Apparatus

• Hydrated iron(II) sulfate (FeSO4.xH2O)

• Spatula

• Bunsen burner, tripod and gauze

• Heatproof mat

• Evaporating basin

• Tongs

• Electronic balance

• Stopclock

Method

1. Weigh evaporating basin and record mass value in results table

2. Keep evaporating basin on balance and add between hydrated iron(II) sulfate crystals

3. Record mass of the evaporating basin and crystals in results table

4. Place on gauze and heat gently for two minutes

5. Allow to cool and reweigh, recording masses in results table

6. Repeat until mass readings are the same (constant mass) so all water of crystallisation is removed

Observations

• Steam given off from hydrated solid as it is heated

• Can be colour change in hydrated solid

• Crystals may break down into to a powder

Results

Use masses recorded in table to find mass of water of crystallisation

Error

not making sure flame is half open so it’s heated gently

Safety

• Wear safety goggles as solid may spit when heated

• Gentle heating to reduce risk of spitting

• Heating could cause FeSO4 to decompose into iron(III) oxide and sulfur dioxide, so use well-ventilated lab

• Allow hot apparatus to cool before touching it, to reduce the risk of burns

• Iron(II) sulfate has a caution hazard symbol on the bottle

• Wash hands if it touches your skin