Types of Burettes in Acid-Base Titration

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Scientists use acid-base titration to determine the amount of acid in a liquid such as vinegar or the amount of base in a beauty product like shampoo. To carry out the titration, they slowly add an acid to a basic solution -- or a base to an acidic solution -- using a piece of lab equipment called a burette -- or burette. An indicator added to the solution changes colour when the base -- or acid -- is neutralised. The burette shows how much acid or base was added to reach that point.


Simple burettes are cylinders of glass with a narrow tip at one end. When used, a burette is attached to a stand with its narrow tip placed in a beaker below. An acid or base solution is poured into the top of the burette using a funnel. Just above the tip is a stopcock for controlling the release of the solution. Wide and narrow lines -- graduations -- along the side of the burette indicate the volume of solution released when the stopcock is opened. The wide lines are marked with the volume, such as 13 millilitres. The numbers increase toward the tip so the volume of solution released can be easily determined.


Self-zeroing -- also known as auto-fill -- burettes are actually attachments for standard single burettes. The self-zeroing kit consists of a plastic bottle that attaches directly or by a flexible tube to the burette. This allows the often hazardous acid or base solution to be added to the burette without using an open funnel. The bottle is squeezed to fill the burette to just above the zero volume graduation. When the bottle is slowly released, excess solution is drawn back into the bottle, allowing the user to adjust the solution easily in the burette to the zero line.


Digital burettes function the same way as simple burettes, except the release of the solution through the burette tip is controlled by a battery-powered stopcock. The entire device attaches to the top of a bottle, and the solution is siphoned into the burette without using an open funnel. With a simple burette, users read the volume by looking at the graduation lines, but a digital burette allows users to release more precise amounts of solutions, using a digital display and control.


Burettes also differ in their precision. Two general classes of burettes exist, according to ASTM International. Class A -- precision grade -- burettes are used for titrations that require the most precise measurements and are labelled with the letter A and a permanent serial number. Class B -- general purpose -- burettes look like class A burettes except their measurements are less precise and they do not have a letter or serial number.

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