Table 2.6 Precision limits for laboratory equipment used in volumetric analysis
burettes ± 0.02 cm^3 for each reading
pipettes (to deliver) (5 ± 0.01) cm 3(^) (10 ± 0.02) cm^3
(25 ± 0.03) cm^3
(^) (50 ± 0.05) cm^3
(^) (100 ± 0.08) cm^3
volumetric flasks (to contain) (25 ± 0.03) cm 3
(^) (50 ± 0.05) cm^3
(^) (100 ± 0.08) cm^3
(^) (250 ± 0.12) cm^3
(500 ± 0.15) cm^3
(^) (1 000 ± 0.30) cm^3
(^) (2 000 ± 0.50) cm^3
analytical balances (to weigh to) ± 0.0001 g
where Mr represents the relative molecular mass of the compound.
The results of an analysis are as follows:
weight of bottle + Na 2 CO 3 (1) 16.254 1 ± 0.0001 g
weight of bottle + Na 2 CO 3 (2) 16.041 9 ± 0.0001 g
weight of Na 2 CO 3 used 0.212 2
final burette reading 45.21 ± 0.02 cm^3
initial burette reading 0.52 ± 0.02 cm^3
volume of HCl used 44.69 cm^3
The overall precision of the weighing is now computed using equation (2.11).