[r-kaede]

A standard of Pb2+ for a gunshot residue analysis using ICP-OES is
prepared by first dissolving 1.0390 g dried Pb(NO3)2 in ultrapure water
containing 1% nitric acid. The solution is brought to volume in a class A 500
mL volumetric flask with an uncertainty of ± 0.20 mL.  This solution is diluted
1/10 by taking 10 mL with an Eppendorf pipette, tolerance ± 1.3 µL) and
diluting this in 1% nitric acid to a final volume of 100 mL in a volumetric flask
with a tolerance of ± 0.08 mL. The balance used for weighing the Pb(NO3)2 has
an uncertainty of ± 0.0002 g.  The atomic weights are as follows: Pb = 207.2; N
= 14.01; O = 16.00.
 
(i) Calculate the concentration of the final solution in mg L-1 of Pb2+
and report the answer with an appropriate number of digits

i've got the final answer of pb2+ to be 6499.631665mgL-1 exactly. i really don't understand the 'number of digits' part of the question. does it want the final answer to be 3 sig. fig?

[Borek]

No idea what they mean exactly. Looks like error propagation analysis to me (not that I know how to do it in a correct, systematic way). For my own purposes I would try some kind of crank three times method: http://www.av8n.com/physics/uncertainty.htm#htoc25 but I don't know if that would be accepted.

[r-kaede]

well i don't think its error propagation...caused the third question asked for error propagation.i just don't get what the question wants from the appropriate number of digit part

[Arkcon]

Write all the numbers down in a column instead of imbedded in a word problem, as it is here.  Review the rules your textbook gives for significant figures (many people are out of practice with those), and round the final answer with the correct significant figures.  And don't be too shocked if the answer key or professor gets it wrong.

[r-kaede]

got it thanks...it wants me to round off the answer