Calibration of Glassware [PDF]

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Title: Calibration Of Glassware



Requirements:          



Tap water Weighing balance Thermometer A 150 cm3 beaker A 100 cm3 beaker A 250 cm3 conical flask A 200 cm3 volumetric flask A 50 cm3 burette A 5 cm3 pipette A 25 cm3 pipette



Introduction The ability to measure the exact volume of solution is crucial for the accuracy of chemical purposes. Volumetric glassware, while made according to known standards, is never perfect. For work of the highest accuracy, it is advisable to calibrate all apparatus. The calibration procedure involves determination of the weight of water contained in or delivered by the particular piece of apparatus. The temperature of water is observed, and from the known density of water at that temperature, the volume of water can be calculated. Thus the exact capacity of the glassware can be determined.



Note: the temperature of water used for the experiment is assumed to be constant for each experiment carried out.



Precaution to be taken: Ensure that the glassware is well washed. Ensure that the glass wall is not wet above the meniscus. Read meniscus without parallax error.



Procedure Calculating the density of water which will be used for the experiment Temperature of water observed = 27 °C Mass of filled densitometer



/g



43.236



Mass of empty densitometer /g



12.947



Mass of water



30.289



/g



Density of water = (30.289 / 25) = 1.211 g/cm3



Calibration of the 150 cm3 and 100 cm3 beaker Both beakers are dried and their initial mass is recorded. Then 150 cm3 water is added to the beaker which is adjusted to the meniscus using a bulb pipette. The mass of the beaker is then recorded. The weighing is done to get three values of mass. The difference of the masses gives the mass of water. The same procedure is done for the 100 cm3 beaker and the mass is obtained.



Results 150 cm3 beaker Mass of beaker + water /g



235.163



235.125



Average 235.148 235.148



Mass of empty beaker /g



84.216



84.216



84.216



Mass of water



/g



84.216 150.929



100 cm3 beaker Mass of beaker + water /g



141.396



141.394



Average 141.399 141.396



Mass of empty beaker /g



50.149



50.149



50.149



Mass of water



/g



50.149 91.247



Calibration of the 250 cm3 conical flask The conical flask is dried and the initial mass is taken. Water is then poured and is adjusted till the mark using the pipette. The mass of the filled flask is taken. The weighing process is done three times and the mass is obtained by doing average. The differences in masses give the mass of water. Results 250 cm3 conical flask Mass of flask + water /g



332.743



332.862



332.907



Average 332.837



Mass of empty flask /g



94.841



94.841



94.841



94.841



Mass of water



/g



242.996



Calibration of the 200 cm3 volumetric flask The volumetric flask is dried and the initial mass is taken. Water is then added and is adjusted till the mark using the pipette. The mass of the filled flask is then taken. The weighing process is done three times and the mass is obtained by doing average. The differences in masses give the mass of water.



Results 200 cm3 volumetric flask Mass of flask + water /g



283.078



283.099



283.23



Average 283.136



Mass of empty flask /g



84.100



84.100



84.100



84.100



Mass of water



/g



199.036



Calibration of the 50 cm3 burette (using 100 cm3 beaker) The weighing vessel is dried and the mass is weighed. The burette is filled up above the zero mark. The distilled water is then adjusted to the zero mark by letting it flow through the tap. Precaution should be taken so as not to wet the glass above the zero mark and parallax error should be avoided while setting the liquid to the zero mark. Then the distilled water is allowed to flow in the weighing vessel and the mass is weighed. The procedure is repeated 2-3 times. Results 50 cm3 burette Mass of beaker + water /g



105.079



105.101



105.098



Average 105.92



Mass of empty beaker /g



50.149



50.149



50.149



50.149



Mass of water



/g



52.994



Calibration of the 5 cm3 25 cm3 pipette (using 150 cm3 beaker) The weighing vessel is dried and the mass is weighed. The pipette is filled up above the meniscus by using pipette filler. The outside of the pipette tip is dried by using a tissue paper. The water is adjusted to the meniscus by releasing the liquid. Then the water is allowed to run off in the 150 cm3 beaker, while the pipette tip touches the inclined wall of the vessel. At the moment when the meniscus comes to a standstill inside the pipette tip, the waiting time is measured. After 15 seconds, the tip is wiped off against the inside of the vessel. If a drop still adheres to the tip, it is wiped off against the inner wall of the beaker. The mass of the beaker is then measured again. The same procedure is repeated with the 25 cm3 pipette. Results (using 150 cm3 beaker) 5 cm3 pipette Mass of beaker + water /g



89.403



89.380



89.368



Average 89.384



Mass of empty beaker /g



84.216



84.216



84.216



84.216



Mass of water



/g



5.168



25 cm3 pipette Mass of beaker + water /g



109.324



109.325



Average 109.338 109.329



Mass of empty beaker /g



84.216



84.216



84.216



Mass of water



/g



84.216 25.113



Calculation of the volume v20 of the gravimetric test results 150 cm3 beaker V20 = (W2 - W1). Z = (235.148 - 84.216). 1.00446 = 151.605



100 cm3 beaker V20 = (W2 - W1). Z = (141.396 - 50.149). 1.00446 = 91.654



250 cm3 conical flask V20 = (W2 - W1). Z = (332.837 - 94.841). 1.00446 = 239.057



200 cm3 volumetric flask V20 = (W2 - W1). Z = (283.136 - 84.100). 1.00446 = 199.924



50 cm3 burette (using 100 cm3 beaker) V20 = (W2 - W1). Z = (89.384 - 50.149). 1.00444 = 55.188



5 cm3 pipette (using 150 cm3 beaker) V20 = (W2 - W1). Z = (89.384 - 84.216). 1.00444 = 5.191



25 cm3 pipette (using 150 cm3 beaker) V20 = (W2 - W1). Z = (109.329 - 84.216). 1.00444 = 25.224



% Error of calibration



=(



=



+



–



) * 100



, where d2 is the density of water calculated from the densitometer d1 is the density of water used for calibration of each glassware



Density for each glassware 150 cm3 beaker Volume used = 150 cm3 Mass of water = 150.929 g Density = (150.929/ 150) = 1.006 g/cm3



100 cm3 beaker Volume used = 100 cm3 Mass of water = 91.247g Density = (91.247/ 100) = 0.992 g/cm3



250 cm3 conical flask Volume used = 250 cm3 Mass of water = 242.996 Density = (242.996 / 250) = 0.971 g/cm3



200 cm3 volumetric flask Volume used = 200 cm3 Mass of water = 199.036 g Density = (199.036 / 200) = 0.995 g/cm3



50 cm3 burette Volume used = 50 cm3 Mass of water = 52.994 g Density = (52.994 / 50) = 1.059g/cm3



5 cm3 pipette Volume used = 5 cm3 Mass of water = 5.168 g Density = (5.168 / 5) = 1.034 g/cm3



25 cm3 pipette Volume used = 25 cm3 Mass of water = 25.113 g Density = (25.113 / 25) = 1.004 g/cm3



% Error for 150 cm3 beaker = 0.0002, d2 = 1.211 g/cm3, d1 = 1.006 g/cm3 =[(



)+(



)] * 100



= 16.9 %



% Error for 100 cm3 beaker = 0.0002, d2 = 1.211 g/cm3, d1 = 0.992 g/cm3 =[(



)+(



)] * 100



= 18.1 %



% Error for 250 cm3 conical flask = 0.0002, d2 = 1.211 g/cm3, d1 = 0.971g/cm3 =[(



)+(



)] * 100



= 19.8 %



% Error for 200 cm3 volumetric flask = 0.0002, d2 = 1.211 g/cm3, d1 = 0.995 g/cm3 =[( = 17.8 %



)+(



)] * 100



% Error for 50 cm3 burette = 0.0002, d2 = 1.211 g/cm3, d1 = 1.059 g/cm3 =[(



)+(



)] * 100



= 12.6 %



% Error for 5 cm3 pipette = 0.0002, d2 = 1.211 g/cm3, d1 = 1.034 g/cm3 =[(



)+(



)] * 100



= 14.6%



% Error for 25 cm3 pipette = 0.0002, d2 = 1.211 g/cm3, d1 = 1.004 g/cm3 =[( = 17.1 %



)+(



)] * 100