For chem lab, you will have a manual which will contain all of the experiments that you will do. There is a introduction to the topic and instructions how to complete the lab. Before every lab, you will complete pre-lab questions and turn them in. After the lab, you have to write a lab report for the next week. The stuff you do in lab does not usually match up with lecture. The amount of time you spend in lab is up to you. If you are quick, you can get out in an hour and a half.
Bio lab is different because the lab and lecture are coordinated. In class, you have clicker questions and they usually outline what you do in lab. Then in lab, you have quizzes and perform different experiments. You also write 2 scientific papers on the experiments and create a poster and present it. You are usually kept in lab for the full 3 hours. Hope this helps.