As part of the procedure for the determination of the sulfate content of an unknown sample it will be necessary to accurately determine the empty weights of a set of crucibles.
This is accomplished by first cleaning the crucible and then heating them in the flame of a Tirrel burner. They are then cooled and weighed. This process of heating and cooling is repeated until successive weighings agree to within 0. The procedure will, in addition, acquaint the student with the use of the analytical balance and the proper use of the desiccator.
Be sure that you read the appendix section dealing with the use of desiccator. Wash and rinse four 10 ml crucibles and their lids. Identify each of the crucibles by means of existing visual differences. Carefully note in your lab notebook what these identifying marks are and assign a number to each crucible.
Do not use marking pens or pencils to mark your crucibles. The high heat which will be used to take them to constant weight will obliterate such markings and more importantly will affect their weight in an unpredictable manner. The lids to the crucibles do not need to be taken to constant weight, however, they should be clean. Place a Tirrel burner under the crucible and adjust the flame of the burner to give a non-luminous flame with a full gas supply.
The tip of the flame cone should be just below but not touching the crucible. Heat the crucible at red heat in this manner for minutes. Allow it to cool for a few minutes and then place it in the desiccator.
Reheat and reweigh it until successive weighings agree to within 0. After cooling, rinse carefully with water and — if necessary — mechanically clean in an ultrasonic bath. Rinse again and finally boil in distilled water to completely remove the hydrofluoric acid. The easiest way to melt metal into liquid is to heat it in a small, enclosed vessel that is heated from below.
You can make your own using a small empty propane tank or metal bucket, plaster of paris, sand, metal pipe, charcoal briquettes, and a steel can. Skip to content Users questions. April 30, Joe Ford. Table of Contents.
And ron's answer was simple and short, while I went on telling grandma stories! Add a comment. Active Oldest Votes. Improve this answer. I'd like to add three things they didn't mention: The balance pan will heat up, too, causing metal parts in the balance to expand. Fred Senese Fred Senese 5, 19 19 silver badges 37 37 bronze badges. Alex Clark Alex Clark 9 1 1 bronze badge. Jan Raina Raina 1. Featured on Meta. Now live: A fully responsive profile. Version labels for answers.
Related 3. Hot Network Questions. Question feed. Chemistry Stack Exchange works best with JavaScript enabled. Accept all cookies Customize settings. That's why the mass of the crucible must be stabilized.
This is very important in gravimetry, it is a basic rule. Glassware should not be heated before it has dried completely. This is because it can greatly decrease the effectiveness and strength of the glass while it is being heated. Yes, you should always be sterile before performing any experiment as to not add any variables.
It depends on what your experiment was. You should ask a teacher or someone that you know who has done this before. The instructor should explain the experiment and advise what safety equipment should be used. Now what you are doing and be organized. A manipulated variable. You should clean metals before trying an experiment to ensure that nothing an accounted for is introduced into the experiments. Chemicals and other substance, if left on your tools, can affect the outcome of your experiment.
There are several ways to make an experiment more valid. For example, one should always make any experiment repeatable, and they should conduct several trials before publishing results or coming to conclusions. The terminals should not get heated up. If one is getting heated up it probably has a dirty connection.
Ventilate the area and let the battery cool down before working on it. To eliminate confounding variables, or variables that were not controlled and damaged the validity of the experiment by affecting the dependent and independent variable, the experimenter should plan ahead. They should run many checks before actually running an experiment.
The inoculating loop should be heated until it is hot enough to turn red, and then allowed to cool for a couple seconds. This ensures that the heat kills the majority of lingering bacteria before or after use. Read all procedures thoroughly before entering the laboratory. An experiment should be designed to answer a specific question. A experiment should only have one variable.
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