In the chemistry lab you are physically manipulating properties of matter so a good lab report is largely dependent on technical lab skills. Since precision is important to achieve the expected experiment results, communicating the results with clear, concise, and comprehensive writing is also important.

Writing Guide for Chemistry from Oregon State University Writing Centre

This website outlines the conventions of writing chemistry lab reports and covers verb tense, person, writing ethics, great examples of clear and concise writing with practice exercises in chemistry lab reports, and information on accessing a chemistry style manual.

Guide to Writing a Lab Report for Chemistry and Biochemistry Students. Concordia University, Student Learning Services

The website describes the purpose of the following sections of a biochemistry lab report: abstract, introduction/theory, experimental procedure, results, discussion, and conclusion.