They have one tapered end to deliver precise liquid measurements and a stopcock rubber stopper used to control the flow of liquid in titrations. The stopcock can be turned to allow small amounts of liquid to flow out of the tube. Burettes are commonly used to measure precise, variable volumes of solution, primarily for titration, and mixing a known measurement of one reactant until the precise reaction is achieved.
Pipettes are measuring devices used to deliver liquids in tiny amounts. They are long, narrow glass tubes with tapered ends and a bulb in the center. They have a hash mark to indicate when they are full.
Scientists use a small rubber bulb to draw liquid into the tube and transfer it to another container or mixture. These steps should help produce a precise measurement. If you are using volumetric glassware, the expected deviation will be indicated on the side of the glassware. Dirty Glassware — In order for a measurement to be precise, laboratory glassware must be clean and dry. Dirt, film, residual liquid, grease, or other contaminants prevent liquid from draining properly.
This can result in a measurement that is either more or less than intended or is a contaminated sample. Before using, make sure your labware is clean, residue-free, and dry.
One good way to ensure the removal of fluid residue is to rinse the glassware several times with a suitable solvent. Meniscus Miscalculation — When filling a pipette or volumetric flask to a specific volume, the level of the liquid must be exactly at the fill-level hash mark. Liquid is not flat, it has a slightly curved surface, called a meniscus.
This can deceive the eye. Wrong Temperature — Volumetric flasks are marked with volume, temperature, and accuracy readings. The T. This is followed by a temperature in celsius, and finally, the accuracy you can expect from the measurement. This might look like:. There are plenty of necessary things to consider when equipping a lab. While pipettes may not seem like much on the outset, even these small expenses can add up to a big bite out of your budget.
To cut your expenses and save money for all the small and not-so-small costs of setting up and running a lab, we offer a cost-effective solution to some of your biggest headaches. Learn more about leasing lab equipment and help keep your lab under budget and within reason. Alternatively, a beaker may be covered with another larger beaker that has been inverted, though a watch glass is preferable.
These beakers are the most accurate you can find. Email Us. Call Us Recents Posts. Value entered for e-mail is invalid Passwords don't match Please fill up missing fields below.
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The most important moment is reading the volume; with burette, the volume is always read twice: first to read the starting position of the meniscus and the second time to read the end position. As the difference in volume is calculated, it is not important how exactly the volume is read, it must however be read in the same way every time. According to the way of operation, manual and electronic pipettors can be distinguished. In manual pipettors , the piston is moved by a thumb using an operation knob.
Accuracy and precision of pipetting depend on expertise of the operator. In case of electronic pipettors, the piston is moved by a small electric motor. Different speeds of aspiring and expressing of the liquid can be selected according to properties of the pipetted solution. Checked version of the article can be found here.
See also comparation of actual and checked version. Forward pipetting This is the most frequently used technique. In forward pipetting, an exactly set volume of liquid is aspired to the tip and then it is delivered to a new vessel.
This technique is recommended for pipetting of diluted aqueous solutions, bufers, diluted acids and bases. Forward pipetting brings a small error in the delivered volume as a thin film of pipetted solution remains on the inner walls of the tip.
In other words, according to the described procedure a slightly smaller volume than required is delivered. This error depends on properties of measured liquid and of the tip. The error can be avoided if the inner wall of the tip is pre-rinsed with the measured liquid. Practically, liquid is first aspired to the tip. Then it is not delivered to a new vessel but returned back to the stock vessel.
Now, a very thin film of pipetted liquid covers the inner wall of the tip it is usually invisible. Pipetting according to instructions given above follows without changing the tip.
As the volume of liquid remaining in the tip is practically constant, exactly the set volume is measured. Reverse technique In reverse technique, a larger volume of solution is aspired to the tip.
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