“Chemical reaction vs. glass test tube” experiment

How to melt a test tube with the heat of the chemical reaction

It’s very im­por­tant for chemists that the ves­sels they con­duct ex­per­i­ments in are durable. But do re­ac­tions ex­ist that can melt glass ves­sels?

Warn­ing! Don’t try to re­peat this ex­per­i­ment with­out a pro­fes­sion­al su­per­vi­sion!

Safe­ty pre­cau­tions

Safe­ty rules must be ob­served when work­ing with flame and heat­ed ob­jects, and the ex­per­i­ment must be car­ried out in pro­tec­tive gloves, glass­es and a mask.

Reagents and equip­ment:

  • test tube;
  • stand;
  • potas­si­um ni­trate (15 g);
  • char­coal (1 g);
  • sul­fur (3 g);
  • fun­nel;
  • gas burn­er.

Step-by-step in­struc­tions

Fix the test tube to the stand, and put a fun­nel on it, through which we add potas­si­um ni­trate. Then melt the ni­trate with the gas burn­er. Then add char­coal. It re­acts with the potas­si­um ni­trate with the re­lease of heat, but the test tube with­stands this tem­per­a­ture on­slaught. Then we add a few pieces of sul­fur. The test tube be­comes in­can­des­cent, and the glass sags and melts.

Pro­cess­es de­scrip­tion

Potas­si­um ni­trate is a strong ox­i­diz­er. If it is melt­ed, its strength in­creas­es from the re­lease of oxy­gen in ther­mal break­down:

2КNO₃ = 2KNO₂ + O₂

If char­coal is added to the test tube, it will re­act with the potas­si­um ni­trate with the re­lease of a great amount of heat:

4КNO₃ + 5С = 2К₂­CO₃ + 2N₂ + 3CO₂

Thus, the re­ac­tive mix­ture heats up to 900 °C (1652 °F, 1173 K). When sul­fur is added, the re­ac­tive mix­ture heats up so much (1820°C, 3308 °F, 2093 K) that the tem­per­a­ture is suf­fi­cient for the glass test tube to melt.

2КNO₃ + 4S = К₂S + N₂ + 3SO2

Try it