Department of Energy Argonne National Laboratory Office of Science NEWTON's Homepage NEWTON's Homepage
NEWTON, Ask A Scientist!
NEWTON Home Page NEWTON Teachers Visit Our Archives Ask A Question How To Ask A Question Question of the Week Our Expert Scientists Volunteer at NEWTON! Frequently Asked Questions Referencing NEWTON About NEWTON About Ask A Scientist Education At Argonne Heating Lemon Juice
Name: debbie
Status: educator
Grade: K-3
Location: TX
Country: N/A
Date: 1/24/2006


Question:
Why is lemon juice clear on paper, but when heated turns brown?


Replies:
Lemon juice contains compounds that are easily oxidized (reacts with air). Heating the lemon juice, especially on a substrate such as paper where the much of the juice is exposed to the air, will speed up the oxidation (heating causes most reactions to speed up). The product of the oxidation is darker in color (brown) then the starting compounds. Hence the "invisible ink effect". If you were to let a piece of paper impregnated with lemon juice just sit out it will eventually turn brown -heating just speeds things up.

Greg (Roberto Gregorius)



Click here to return to the Chemistry Archives

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (help@newton.dep.anl.gov), or at Argonne's Educational Programs

NEWTON AND ASK A SCIENTIST
Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Weclome To Newton

Argonne National Laboratory