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Unformatted text preview: ing about centrifuging is to balance the centrifuge; put a test tube of the
same size and design opposite the test tube to be centrifuged. The test tube can be filled with tap
water if necessary (do NOT dilute another solution
with tap water; instead, place it in its own slot and
balance the centrifuge). If the centrifuge is not
properly balanced, it is very easy to severely damage
the centrifuge. If you understand the concept of
vectors, you can balance the centrifuge with three test
tubes as well; ask your instructor for more
Once the centrifuge is balanced, turn it on.
Allow it to run for one or two minutes. If the
centrifuge begins making a lot of noise, turn it off and
check the balance. You must stay with the centrifuge
the entire time it is running, since minor vibrations can cause a centrifuge to “walk” off of the
Dakota State University Page 42 of 232 Basic Laboratory Procedures General Chemistry I and II Lab Manual bench. When you turn it off, allow it to come to a stop itself; NEVER put your hand (or
anything else) above the centrifuge.
Although there are times that one would like to simply pack ice or ice chips around the
outside of a container to keep it cool, it is far more common to use an ice bath. Ice baths are
easier to work with and tend to be more efficient, since they will make more thorough contact
with the container. Start with a bath that is ice, and half or less of water; if too much ice melts (if
the ice does not touch the bottom of the ice bath), pour some of the water out and add more ice,
since this can create isotherms that are warmer than you would like. If you need the ice bath
colder, add salt (usually low grade since it will not be used for a chemical reaction).
Litmus paper will be blue in a basic solution and pink in an acidic solution. Because it is
easier to see color changes, use blue litmus paper to test for acidic solutions (it will turn from
blue to pink) and red litmus paper to test for alkaline (or basic) solutions (it will turn from pink
to blue). Do NOT place the litmus paper into the solution to be tested; instead, put a piece of
litmus paper on the desk, and use a clean glass stirring rod to transfer a drop from the container
to be tested onto the paper. In this fashion, the same piece of litmus paper can be used many
times. Read the litmus paper BEFORE it dries, and never try to use the same spot of a piece of
litmus paper twice.
The oldest trick in the book for testing gas is the “glowing splint” test. Depending on your
reactants, there are a variety of gases that can possibly be given off; this simple little test helps to
distinguish four of these gases: oxygen, hydrogen, carbon dioxide and nitrogen. You perform it
by taking a glowing splint, lighting it on fire, extinguishing the fire such that the splint continues
to glow, and using the splint to test the gases coming off from the reaction. One of three things
If the splin...
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