Burettes dispensing

To make a burette reading, first read and record the liquid volume in the burette, dispense the required amount, and reread the liquid volume in the burette. Then subtract the first reading from the second reading to calculate the amount of fluid delivered. Self-zeroing burettes do not require a first and second reading, because all readings start from 0.00 mL. 

The instrument illustrated in Fig. 7.6a, similar to that described above, has been applied to the photometric titration of weakly acid drugs In the presence of an immiscible solvent. The essential differences between this Instrument and the previous one lie in the use of a spoiler aimed at minimizing vortex formation arising from the utilization of a stirring bar a burette dispensing the titrant or the washing solution and a triple layer of filter paper on the Teflon membrane to allow It to be traversed by the aqueous phase which, in turn, is propelled to the flow-cell by means of a peristaltic pump [5]. 

Figure 13.15 shows the operational scheme of this automatic tltrator. The heart of the unit Is an INTEL 8080 microprocessor mounted on the central processing unit (CPU) board. The rotary reaction cell assembly can accommodate up to three different sensors for multiple measurements on the same processed sample. Each stepper burette board controls up to two burette dispensing assemblies. Function boards such as the colorimeter board, air burette board, E/I output board and RS-232 printer Interface boards are available optionally. The optional D/A and E/I board is used for closed-loop applications where the tltrator controls the final element such as a control valve. The RS-232 printer Interface board Is useful for troubleshooting the equipment and editing user-defined programs. The Instrument accuracy, repeatability and response time vary widely and depend on the particular type of measurement concerned. The system requires a.c. power, a 75-psl air supply and a dilution water supply for proper operation. The air flow-rate required is of about 50 cm3/mln... 

Survey of Odorizing Practice in Gas Transmission, Pet. Engr., Midyear, 1941, p. 114 also Anon., Inexpensive Burette Dispenses LPG Odorant, Natl. Pet. News, July 3, 1946, p. R-498. 

Volumetric analysis involves using a solution of accurately known concentration, a standard solution, in a quantitative reaction to determine the concentration of the other reactant. The procedure is known as titration. One solution is measured quantitatively into a conical flask using a pipette. The other solution is dispensed from a burette until a permanent colour change appears in the solution in the conical flask. 

The titration cycle, Hke most of the other functions, can be repeated at will. Back-titrations are therefore possible, as well as multiple titrations for multi-component analyses. At the end of the cycle, the sample is returned to the sample transport. All dispensing is from a multi-burette system with up to 20 dispensing assembhes, each with a total dehvery volume of 10 or 20 ml. 

Procedure (standard curve). Fill a 50-ml burette with the phosphorus intermediate standard solution and dispense 25, 26, 27, 28, 29, 30 and 31 ml into a series of 100-ml volumetric flasks. These will contain 50, 52, 54, 56,... 

There are four categories of containers used to measure volume volumetric flasks, graduated cylinders, burettes, and pipettes. Of the four, volumetric flasks are used exclusively to measure how much has been put into them. This use is known as to contain. Graduated cylinders and a few pipettes are used to measure how much has been put into them as well as how much they can dispense. The latter measurement is known as to deliver. Burettes and most pipettes are used solely to deliver. 

Like pipettes, Class A burettes have slower outflows than Class B burettes. They allow the user to better control the dispensing fluid. The slower speed also allows... 

The least accurate burettes are Mohr burettes (see Fig. 2.22). Mohr burettes do not have stopcocks at their tips and therefore require flexible tubes with pinch clamps to control dispensing liquid. 

The last type of common burette is the dispensing burette. It is easy to recognize by its size. It can carry up to one liter of liquid and is capable of fast, effective liquid dispensing. Its accuracy is about 0.5% of total volume. 

For intermediate storage, modified Schlenk tubes (Fig. 2.7) may be used. The version with a burette side-arm is particularly convenient for dispensing a measured volume to a reaction vessel. 

A chemist dispenses a titrant, 0.1000 MHCl, from a burette at 25.0°C. The initial reading is taken six times the values (in milliliters) are... 

Consider an analytical method involving the titration of hydrochloric acid with anhydrous sodium carbonate to determine the concentration of the acid. The measurements made are mass (weighing out a chemical to make up a solution of known concentration) and volume (dispensing liquids with pipettes and burettes). The reaction between the two chemicals is based on amount of substance - one mole of sodium carbonate reacts with two moles of hydrochloric acid - and the mass of a mole is known (e.g. the formula weight in grams of one mole of sodium carbonate is 105.99). All the measurements are based on either length or mass and are traceable to SI units, so the method is a primary method. 

Burettes, which can be considered a special form of graduated pipette, are usually filled with a small filter funnel and liquid is dispensed via a tap. They are an essential tool in titrations for determining the concentration of compounds in solution. 

Gas burettes are most commonly used for low pressure hydrogenations (Chapter 14), but they can of course be used for delivering other gases thus providing an easy method of dispensing accurately measured volumes. A simple gas burette design is shown in Fig. 7.5. It is operated as follows ... 

Figure 4.24. Estimated concentiation of ion using the standard addition technique with an ion-selective electrode. The simulated signal traces are for DVM resolutions of 1, 0.1, 0.01, resp. 0.001 mV (left to right). For each resolution the added volume V2 is varied from 2.4 to 2.55 ml in increments of V2 = 10 fi. The ordinate marks indicate the 95-105% SLs. The expanded traces for 0.1. .. 0.001 mV resolution are also given. The simulation was run for five different values of EO = 300 -l- RND [mV]. The vertical drops (e.g., A B) occur at unpredictable values of V2 AV-- 10 /rl would in this case entail an inexplicable AC/Cnom of nearly 8% The traces do not reach the 100% level because a 50 fil error in reading off the dispenser or burette was assumed.

The reagent can be dispensed from a burette or measured by pipette in the latter case the liquid should be drawn into the pipette with a pipetter, not by mouth. 

The amount of titrant added is usually measured by volume (by dispensing the solution from a burette), and in this case, titrimetry is an example of volumetric analysis. Occasionally, the titrant is measured by weight (especially if greater accuracy is required) or by amount of electricity (as in coulometric titrations). 

Aids for BOD determination include syringe-type dispensers for the manganese(II) salt and other solutions, and commercially available digital burettes, which are more convenient than the conventional glass-type ones. 

About 40 g sample is weighed into a 250 ml Erlenmeyer flask. 50 ml of acid number solvent is added by dispensing burette, stirring using a magnetic stirrer until the sample is completely in solution. Five drops of phenolphthalein indicator are added and the solution titrated with OTn alcoholic KOH to the first faint-pink end-point. A blank is determined in the same way, omitting the sample. 

Burette Unit Fisons automatic dispenser Fisons Ltd... 

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