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Apparatus for titrimetric analysis
(a) Weighing bottle
These consist of a cylindrical glass vessel with a ground stopper in which the material can be weighed out of contact with the atmosphere .its usually heated in a steam oven before use to ensure dryness and is then allowed to cool in a dessicator . It should be protected from contamination with fingers during handling (using a dry cloth )
A weighing bottle can be used in two ways (I) by first weighing it when empty then when loaded. This method is tidious ad it’s likely to expose the substance to the atmospheric contamination during the process of weighing . (ii) By weighing an already loaded bottle then pour the substance in a measuring flask then letter weigh the empty bottle and finally calculating the difference in weight
(b) Conical flask
250cm3 capacity is usually used. Conical flask are made to contain a specific volume of liquid and will not deliver that volume because part of that liquid will inevitably remain or retained as a film on the sides of he flask .
- They are usually graded to work at specific temperatures eg 20oc and should be used at temperatures close to these .they should be rinsed before use wit h distilled water or solvent to be used . the solvent should be added from the wash bottle down the sides of the beaker so as to avoid splashing . the flask should thereafter be filled with the solvent to the meniscus mark a teat pipette should be used to add the last drops the flash should then be stoppered and shaken vigorously
- Burette
They usually have a capacity of 50cm3. Some are glass stoppered . Its first washed is first washed /rinsed with solution to be used whereby the solution should run through the jet . Its then filled to the zero mark then read carefully to ensure it’s on the meniscus a sheet of white paper placed behind it . The tap is opened and the required volume is released and worked out by difference
Rough titration is always advisable before doing the real accurate titration. About 1cm3 solution is released at a time into the solution in the conical flask containing an indicator until the indicator changes color theses at end point
Burettes should always be well washed out after use . if incase an alkaline solution have been used in the burette , it should be washed out using about 10cm3 of dilute acid then rinsed using distilled water
- Pipettes
They are designed to deliver a certain volume of liquids . When filled to the mark, it contains more than these volume .the extra volume is always retained after delivery as a film on the sides of the pipette and in the tips .
The pipette is filled past the mark by sucking the solution into it and allowed to slowly drain away. Sunction devices should be used for poisonous or corrosive chemicals . If the solution is sucked by mouth it should spat out at once and the mouth rinsed . . The liquid is retained in the pipette by pressing the forefinger on the open end of the pipette .the tip of the conical flask is then placed inside the conical flask . no attempt should be made to expel the remaining solution from the pipette as the pipette will have already delivered 25 cm3