Lesson: Chapter - 11

Some Common Lab Techniques

Massing solids: When obtaining the mass of solid chemicals, always use some type of weighing paper to protect the pan of the balance. Remember that the mass of the weighing paper must be written down and subtracted from the total weight when you are determining the amount of solid obtained.

Measuring liquids: When measuring out a particular volume of a liquid, you must choose an instrument that will measure as accurately as possible. For small quantities it would be appropriate to use a pipette or burette. For larger quantities a graduated cylinder might be appropriate. Remember that beakers are not accurate measuring instruments! Remember always to take measurements of liquids from the bottom of the meniscus.

Filtering: When filtering a solid from a mixture by gravity filtration, always weigh the filter paper, fold it, place it in the funnel, and wet it down to hold it in place before beginning the filtering process. After filtering, the solid on the filter paper must be dried and weighed. The initial weight of the filter paper is subtracted to find the mass of the solid obtained. The liquid that comes through the filter paper is known as the filtrate.

Color Review

One way to identify elements is by performing a simple flame test in the laboratory. When the electrons are heated, they get excited and jump away from the nucleus. As they fall back down, they release energy, often in the form of visible light. Some of the most common colors of flames are listed. You may recognize many of these from fireworks displays!

Many solutions in chemistry also have color, which is often the result of unpaired electrons. Metal ions often are colored.

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