Bunsen burner: flame test

Safe­ty pre­cau­tions

At­ten­tion! All ex­per­i­ments are per­formed by pro­fes­sion­als. Do not at­tempt.

Process de­scrip­tion

The burn­er flame con­sists of a heat­ing zone, an in­ten­sive com­bus­tion zone, and a lu­mi­nous zone. In the heat­ing zone, hy­dro­car­bon gas­es and oxy­gen are heat­ed by the sur­round­ing blue flame, but do not re­act with one an­oth­er. There­fore, this part of the flame is col­or­less and is lo­cat­ed at the bot­tom, and its tem­per­a­ture reach­es about 350 °C (660 °F). Pass­ing into the in­tense com­bus­tion zone, the gas­es re­act, re­leas­ing a blue glow and a lot of heat. This is the hottest part of the flame, with a tem­per­a­ture of ap­prox­i­mate­ly 1500 °C (2730 °F). The blue col­or is due to the for­ma­tion of rad­i­cals such as OH and CH. These rad­i­cals are high­ly un­sta­ble and do not ex­ist un­der nor­mal con­di­tions; they ap­pear at high tem­per­a­tures. In the flame, these rad­i­cals are in an ex­cit­ed state, that is, they have an ex­cess of en­er­gy. In an ef­fort to move to a more sta­ble, ground state, these par­ti­cles re­lease en­er­gy in the form of blue light. Some gas mol­e­cules do not burn com­plete­ly, form­ing small par­ti­cles of soot. These par­ti­cles rise high­er and are ox­i­dized by oxy­gen, heat­ing up to about 1000 °C (1830 °F) and emit­ting yel­low light. The flame of the burn­er can be used to de­tect met­al ions: they ab­sorb the ther­mal en­er­gy of the flame, which is then emit­ted in the form of light with a char­ac­ter­is­tic col­or. For ex­am­ple, cop­per(II) ions emit green light, sodi­um ions emit yel­low light, and cal­ci­um or stron­tium cre­ate shades of red. In ad­di­tion, the flame’s tem­per­a­ture is high enough to melt glass, caus­ing it to bend and stretch. This time, the flame turns yel­low-or­ange due to the sodi­um and cal­ci­um ox­ides pres­ence in the glass.

Safer (but just as cool) ex­per­i­ments await you in the MEL Chem­istry sub­scrip­tion!