Question

Data Record

1.      Temperature of the water = ______18___ oC

2.      Table for recording mass of flask and aliquots

Mass (g)

Mass of water delivered per aliquot(g)

Flask

95.90

Not applicable

Flask + 1st aliquot of water

120.2758

m1 =25.0758

Flask + 2nd aliquot of water

120.3555

m2 =25.1555

Data interpretation and calculations

Calculate the relative spread of the masses of aliquots delivered.

2.Estimate the density of distilled water at the laboratory temperature using data from Table 1.

3.Determine the average volume of water delivered by the pipette using the relationship:

          .

4.Determine the percentage error of the pipette using the relationship:

              

Discussion

List and discuss the possible sources of error in using a pipette.

Answer 1

wt. of empty flask wt. of flask + water wt. of water taken actual wt. of water

data 1 95.9 gms. 120.2758 gms. 24.3758 gms. m₁ = 25.0758 gms.

data 2 95.9 gms. 120.3555 gms. 24.4555 gms m₂ = 25.1555 gms.

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average wt. of water = ( m₁  + m₂  ) / 2 = 25.11565 gms.

hence , density of water at 18^oC = 25.11565 / 25.00 = 1.004626

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Volume of water = 24.3758 / 1.004626 = 24.26 ml. ----------------as per data 1

Volume of water = 24.4555 / 1.004626 = 24.34 ml. ----------------as per data 2   hence, average volume = 24.30 ml.

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therefore negative deviation / error = 25.00 - 24.30

= 0.70 % error = (25.0 - 24.30) (100 ) / 25

  = (-) 2.80 %   

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Possible sources of errors in using the pipette -

1 ) The pipette may not have been rinsed properly with the water to be filled in and subsequently transferrred

2) The liquid level may not have been filled up to the mark on the pipette such that its lower meniscuss coincides with the mark.

3) The last drop of the water might not have been removed carefully by touching the tip of the pipette with inner bottom of the flask.

.