A research laboratory is required to report the mass percent composition of sodium…
CHEMISTRY · Multi-part · A Level · Chemistry · Amount of substance · Amount of substance
Problem
A research laboratory is required to report the mass percent composition of sodium hydrogen carbonate (NaHCO₃) with an uncertainty that reflects the precision of the balance used. Three replicate weighings give the following data for a single pure sample:
Initial mass of weighing bottle + sample: 12.465 ± 0.003 g
Empty weighing bottle: 10.217 ± 0.003 g
Atomic masses (g mol⁻¹): Na = 22.99, H = 1.008, C = 12.01, O = 16.00.
(a) Determine the mass of the NaHCO₃ sample and its absolute uncertainty.
(b) Calculate the theoretical mass percent of each element in NaHCO₃ using the atomic masses provided.
(c) Propagate the uncertainty from part (a) to report the mass percent of sodium in this particular sample with its associated absolute uncertainty. Assume that the atomic masses are exact for the purpose of uncertainty analysis.
(d) Explain why reporting the elemental composition with an accompanying uncertainty is important when comparing results among different laboratories.