"Christmas Mood" experiment

How to make beautiful "hoarfrost" with benzoic acid

Do you miss win­ter al­ready? Then we’ll show you how to make your own win­ter won­der­land with the help of chem­istry.

Reagents and equip­ment:

  • 15 g of ben­zoic acid;
  • a large beaker;
  • fir branch­es;
  • dry fuel.

Step-by-step in­struc­tions

Place a large beaker on a spe­cial stand. Add 15 g of ben­zoic acid and 3-4 fir branch­es. Place dry fuel un­der the glass beaker and light it. Af­ter a while the beaker will heat up so much that the ben­zoic acid will start to sub­lime, i.e. move from a sol­id to a gas phase, with­out pass­ing through a liq­uid phase. As soon as all the ben­zoic acid evap­o­rates, re­move the fuel and let the beaker cool down. When it has cooled down, the ben­zoic acid va­por will start to set­tle on the fir branch­es and the walls of the beaker. It re­al­ly looks like it’s snow­ing!

Pro­cess­es de­scrip­tion

In this ex­per­i­ment, sol­id ben­zoic acid evap­o­rates with­out pass­ing through a liq­uid phase. The process of mov­ing from a sol­id phase di­rect­ly to a gas phase is called sub­li­ma­tion. When the crys­tals of ben­zoic acid heat, the tem­per­a­ture in­creas­es, the crys­tals melt, and the tran­si­tion to a gas phase takes place. Cool­ing caus­es a re­verse tran­si­tion. When the ben­zoic acid va­por set­tles on the fir branch­es, it cools and crys­tal­izes. The re­verse process of tran­si­tion from a gas phase to a sol­id phase is called desub­li­ma­tion.

Safe­ty pre­cau­tions

In work­ing with ben­zoic acid, wear rub­ber gloves and pro­tec­tive glass­es. Stay at a safe dis­tance from the source of fire and ob­serve fire safe­ty.

Warn­ing! Only un­der pro­fes­sion­al su­per­vi­sion.