Weight burettes

The Lunge-Rey pipette is shown in Fig. 3.3(b). There is a small central bulb (5-10mL capacity) closed by two stopcocks 1 and 2 the pipette 3 below the stopcock has a capacity of about 2 mL, and is fitted with a ground-on test-tube 4. This pipette is of particular value for the weighing out of corrosive and fuming liquids. 

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All titrations were performed using an auto titrator Model AT-97 manufactured by Mayura Analytical Pvt. Ltd., Bangalore, India. This auto titration system consists of a motor-driven titrant dispenser, a mechanical stirrer and electrodes coupled to a pH/ion analyzer and controlled by a personal computer for automatic titration and data acquisition and processing. The titrant was added from weight burette. The e.m.f. readings were recorded with an autotitrator using platinum as indicator electrode and saturated calomel electrode as reference electrode. 

An accurately weighed uranium oxide sample was added to a known excess of standard Ce (IV) solution in nitric acid in a 50 ml beaker and dissolved by swirling the solution with a magnetic stirrer, at room temperature and finally diluted to 2N nitric acid. The dissolution was complete within 2 min. The excess Ce (IV) was then determined by back titration with the same standard OHA solution potentiometrically by weight burette. 

The most commonly used pieces of apparatus in titrimetric (volumetric) analysis are graduated flasks, burettes, and pipettes. Graduated cylinders and weight pipettes are less widely employed. Each of these will be described in turn. 

Calibration of apparatus and application of corrections. All instruments (weights, flasks, burettes, pipettes, etc.) should be calibrated, and the appropriate corrections applied to the original measurements. In some cases where an error cannot be eliminated, it is possible to apply a correction for the effect that it produces thus an impurity in a weighed precipitate may be determined and its weight deducted. 

Note on the gravimetric standardisation of hydrochloric acid. The gravimetric standardisation of hydrochloric acid by precipitation as silver chloride is a convenient and accurate method, which has the additional advantage of being independent of the purity of any primary standard (compare Section 10.38). Measure out from a burette 30-40mL of the, say, 0.1M hydrochloric acid which is to be standardised. Dilute to 150 mL, precipitate (but omit the addition of nitric acid), and weigh the silver chloride. From the weight of the precipitate, calculate the chloride concentration of the solution, and thence the concentration of the hydrochloric acid. 

Prepare 250 mL of 0.02 M potassium dichromate solution and an equal volume of ca 0.1 M ammonium iron(II) sulphate solution the latter must contain sufficient dilute sulphuric acid to produce a clear solution, and the exact weight of ammonium iron(II) sulphate employed should be noted. Place 25 mL of the ammonium iron(II) sulphate solution in the beaker, add 25 mL of ca 2.5M sulphuric acid and 50 mL of water. Charge the burette with the 0.02 M potassium dichromate solution, and add a capillary extension tube. Use a bright platinum electrode as indicator electrode and an S.C.E. reference electrode. Set the stirrer in motion. Proceed with the titration as directed in Experiment 1. After each addition of the dichromate solution measure the e.m.f. of the cell. Determine the end point (1) from the potential-volume curve and (2) by the derivative method. Calculate the molarity of the ammonium iron(II) sulphate solution, and compare this with the value calculated from the actual weight of solid employed in preparing the solution. 

Buffer action 46 Buffer capacity 48 Buffer mixture universal, (T) 831 Buffer solutions 46, (T) 831 acetic acid-sodium acetate, 49 for EDTA titrations, 329 preparation of IUPAC standards, 569 Bumping of solutions 101 Buoyancy of air in weighing 77 Burette 84, 257 piston, 87 reader, 85 weight, 86... 

Calcium, D. of - continued in limestone or dolomite, (fl) 813 in presence of barium, (ti) 333 with CDTA, (ti) 333 with lead by EDTA, (ti) 333 with magnesium by EDTA, 328 by EGTA, (ti) 331 by flame emission, (aa) 804 Calcium oxalate, thermal analysis 498 Calcon 318 Calculators 133 Calibration of apparatus, 87 of burettes, 88 of graduated flasks, 88 of pipettes, 88 of weights, 74... 

Burettes calibrated at 20°C and 25°C deliver different weights of water for each 10 ml, when weighed with standard brass weights in air at 50% relative humidity (RH) at standard atmospheric pressure, as given below ... 

Hence, the true volume for each 10 ml segment of the burette can be calculated from the weights obtained and recorded on a convenient chart. 

Most of the instruments, commonly used in an analytical laboratory, such as UV-Spectrophoto-meter, IR-Spectrophotometer, single—pan electric balance, pH-meter, turbidimeter and nephelometer, polarimeter, refractometer and the like must be calibrated duly, before use so as to eliminate any possible errors. In the same manner all apparatus, namely pipettes, burettes, volumetric flasks, thermometers, weights etc., must be calibrated duly, and the necessary corrections incorporated to the original measurements. 

If R is foe burette reading, W is the weight of acid in 100ml of soln, NF is the normal factor of the NaOH soln, 49.043 is the equivalent weight of H Da(1A of mol wt),. then the percentage of sulfuric acid as HaS04 is determined by the following formula ... 

HN02 (Small Amounts).—5 c.cs. N/10 permanganate solution are diluted with distilled water to 100 c.cs. The mixed acid is then run in from a burette until the KMn04 is decolorised. The weight of mixed, acid is calculated from its specific gravity. 

Some burettes have a tube for easier filling attached between the calibration lines and above the tip. Flexible tubing is attached to the tube used for filling the burette. There are two methods to stop liquid flow. One technique uses a pinch clamp on the flexible tubing, and the other has a stopcock on the side tube. The pinch clamp can lead to inherent errors as the pressure from the weight of the liquid in the burette causes a small expansion of the flexible tube. As the burette is emptied, this pressure decreases, and the amount of error decreases as well. If your work requires limited accuracy, these changes are well within tolerance. Alternatively, a stopcock can be used instead of a pinch clamp. There are no hydrostatic complications with the stopcock. 

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