Residues in your container or spatula may contaminate it. Dispose of excess chemicals according to directions by your instructor. Never put anything down the sink unless you are directed to do so. Most waste will go in labeled containers. Let's protect the environment.
Balances are sensitive, expensive devices.
Never weigh chemicals directly on the pan. Use a container such as a beaker or flask. Remove the container from the balance, add the chemical, then replace the container. If you spill anything onto the balance, notify the instructor immediately. Never lay a stopper from reagent bottles on the lab bench.