What is the purpose of the rubber policeman on a stirring rod?

to transfer residues of precipitate or solid on glass surfaces when performing gravimetric analysis.

Explanation:

A policeman is a hand-held flexible natural-rubber or plastic scraper. The common type of it is attached to a glass rod and used in chemical laboratories to transfer residues of precipitate or solid on glass surfaces when performing gravimetric analysis.

  the   balanced   equation   for   reaction of   ca metal   with   o2 to   produce   cao   is as below

2 ca+ o2→ 2 cao2

  explanation

the reaction is   balanced     since the   number of atoms   in reactant side is   equal to   number of atoms   in   product side.   for   example   they   are 2   atom of   ca in   reactant   side   and   2   atoms of ca   in   the product side.

  the   process   is a   meet the   requirement   of   redox   reaction because :     calcium   is   oxidized   from   oxidation state 0   to 2+   while   oxygen   is reduced from   oxidation   state   0   to 2-

1.43 x 10^-11 j the guy commented the awnser just making sure u see it .