# Decanting/Wafting

Decanting – gradually pouring off liquid from a mixture.

Do This:

In front of you should have a mixture of water and sand. Your goal is to pour the water into an empty beaker with out pouring out any sand. See how much water you can pour off? What techniques did you find most effective in decanting the water?

Wafting – sampling a small amount of odor by pushing the air above the sample in a waving motion towards your nose.

Do This:

Take a test tube filled with the odor and carefully remove the stopper. Bring the test tube approximately 10 inches from your nose with one hand and with the other gently wave your hand toward your nose. This action should bring a small amount of air from above the test tube towards your nose.

Story: Jeff was a 250 lbs. lineman on my high school football team, needless to say a big guy. One day in lab, Jeff was working with a sample of an ammonia solution. Maybe it was because he thought he was so big and tough he decided to ignore the teacher’s advice (to waft the ammonia odor in his sample). He put his nose right over his beaker and inhaled. BOOM! All 250 lbs. hit the floor immediately. Jeff passed out from the large dose of ammonia vapor.

(Liquid Measurements)

Meniscus – the lowest point of the surface of water as it sits in a container.

Water has something called surface tension. It is this surface tension that allows water droplets to form on a surface. It also causes water to “stick” to the sides of glass. To make accurate measurements of volume when dealing with water you must measure from the meniscus.

Do This:

1) Pour some water into a graduated cylinder. Can you find the meniscus? Measure the volume of water in the graduated cylinder from the meniscus.

2) Put a drop of water between two overhead slides. What happens?

3) Volumetric Flasks are used to make specific volumes of solution. Using the faucet and an eyedropper try to get the meniscus to the exact volume line on the neck of the glassware. What techniques were most effective?

# Balances

The balance should be zeroed – with nothing on the tray the balance pointer points to the centerline. If not turn the adjustment knob below the pan a little bit, then check the balance pointer again. Adjust until the balance pointer rests at the centerline.

Mass an object by adjusting the counterweights until the balance pointer returns to the centerline.

Test tubes (cleaning and drying)

Test tubes are tricky items to wash. We will need to wash all the glassware we use in lab so that they will be ready for our next lab and we won’t contaminate our next experiment. Practice washing some test tubes with the scrub brush.

1) Put water from the tap with a small amount of soap into the test tube.

2) Scrub with the brush.

3) Rinse THREE times with water.

4) Roll a paper towel into a tight cylinder and insert into the test tube to dry it

5) Place inverted on the test tube rack for more drying and storage.

# Burette

A Burette is used to dispense a known volume of liquid one drop at time. You turn the plastic knob or stopcock up and down to dispense the liquid and horizontal to stop the flow of liquid.

Try it out.

How do you dispense a KNOWN amount of liquid from a burette?

Give the steps for determining the amount you dispense.

Powders

Scupula

The scupula is used to remove the powder from its storage container. Never put material back into the storage containers. Always have a disposal beaker to put excess material in if you take too much (it gets thrown away, so don’t use too much)

## Mortar and Pestle

The mortar and pestle is used to grind substances into fine powders.

## Rubber Policeman

The rubber policeman is used to aid in transferring powders from one container to another.

Do This: Use the scupula to remove some NaCl (table salt) from the storage container into the mortar and pestle. Grind up the salt into a fine powder (use a rotating motion as opposed to a pounding motion – its too messy, just imagine that the powder is dangerous and you don’t want to spill it). Transfer the fine powder to a beaker with a rubber policeman.

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