Burette: Definition & Function in the Laboratory

Burette: Definition & Function in the Laboratory
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  • 0:00 What is a Burette?
  • 1:04 What Do Burettes Measure?
  • 2:09 Example
  • 4:04 Other Measurements
  • 4:25 Lesson Summary
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Lesson Transcript
Instructor: Gail Marsella
Learn the parts of a burette and how to use one to obtain analytical data important in answering real questions. For example, can we figure out how much acid is in a can of Sprite?

What Is a Burette?

Perhaps you've heard the story about a tooth dissolving in a soft drink overnight, with the implication that all that acid must therefore make Coke or Sprite too poisonous to drink. Well, no. It is true that a tooth placed in any soft drink will eventually dissolve after sitting there for many days. And, it is true that soft drinks contain citric and/or phosphoric acids (mostly to improve flavor tartness), but your stomach is perfectly capable of digesting those chemicals. And, you can protect your tooth enamel by brushing regularly. Fruit juice actually has more acid than soda.

Well, okay, but how much acid is in a can of, say, Sprite? How would we find out? We have to do a titration, a chemical reaction between the acid in soda and another chemical (a base) to neutralize it. The main piece of laboratory equipment we'll use for this process is known as a burette, a long glass tube with volume markings and a stopcock at the bottom to start and stop liquid flow.

What Do Burettes Measure?

The volume markings (also called graduations) on a burette start at zero on top, and increase going down. A standard size laboratory burette can deliver up to 50.00 milliliters (mL) of liquid. (Other specialized burettes are larger or smaller.) The volume markings are precisely positioned at 0.1 mL increments so that you can read the volume to the first decimal place, and then estimate the second decimal place.

Liquid in a burette takes a curved shape called a meniscus. It is important when reading a burette to read the bottom of the meniscus. This tends to be more precise than reading the top of it. Sometimes it helps to place an index card with a thick black line on it behind the burette to reduce glare when reading it.

A single reading on the burette won't tell you very much. However, if you take an initial reading, open the stopcock to let some liquid flow into a flask, and then take a final reading, the difference between those two numbers is the amount of liquid delivered to the flask. Let's look at a titration using a burette. Albert (Al) Chemist is doing the analysis.

Example

Acids and bases neutralize each other: one hydrogen ion plus one hydroxide ion makes one molecule of water. For this titration, Al Chemist will react a hydroxide solution of known concentration with the acids in a clear soda: Sprite.

Bubbles would make the volume of Sprite difficult to measure accurately, so Al lets a can of Sprite sit out overnight and go flat. Then he measures out exactly 25.00 mL of the liquid with a pipette, another piece of laboratory glassware that measures only a single volume (in contrast to a burette, which can deliver variable volumes as needed.) He places the Sprite in a flask and adds a few drops of an indicator chemical that will change color when the acid is completely neutralized.

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