[lulu.bela]

hi , I tried solving this question but i couldn't , please help me solving it (thanks in advance):
A student wanted to prepare 100 mL of a 1.000 g L-1 solution of NaCl and devised the following method. The student weighed 0.100 g of solid NaCl on a balance and transferred this to a 100 mL volumetric flask. Sufficient water was then added, with stirring, to give a final volume of 100 mL according to the mark on the volumetric flask.

Given that the uncertainties in the balance and volumetric flask were ±0.001 g and ±1 mL, respectively, calculate the final uncertainty in the concentration of the NaCl solution. Did the student succeed in preparing a 1.000 g L-1 solution? If not, what was the concentration, including the uncertainty, of the solution?

note
rules:
While significant figures and uncertainties are related, the rules for determining the uncertainty in the answer of a calculation are somewhat different from those for significant figures on the previous page. They are as follows:
   

•  When two or more numerical measurements are added or subtracted, the uncertainty in the final answer is the sum of the absolute uncertainties in the measurements.

•  When two or more numerical measurements are multiplied or divided, the uncertainty in the final answer is the sum of the percentage uncertainties in the measurements.

WORKED EXAMPLE:
In an experiment, 2.400 g of CoSO4·7H2O was heated to remove the water of crystallisation until no further mass loss was observed. At this point, the mass of anhydrous CoSO4 obtained was 1.323 g. Use these figures to calculate the percentage, by mass, of H2O in CoSO4·7H2O, and give the uncertainty in your final answer. Note that the balance used to weigh the samples has an absolute uncertainty of ±0.001 g.

Edit: attachments deleted, possible copyright violations.

[Squeegy]

hey,
i think your worked example has far more information than you need, the way i would do this is do error/measurement amount for both measurements to get their relative uncertainties (both of which are 1/100), and then add the relative uncertainties to get the relative uncertainty in the final concentration (2/100), finally you multiply the relative uncertainty by the final concentration to get the uncertainty in your result (±.02 g/L)
(i use relative uncertainties here, but its effectively the same as a percentage uncertainty, to convert to percentage, you just multiply by 100)

as to if the student made a 1.000 g/L solution, technically they made a 1.00 g/L ±.02 solution, because the uncertainty means any figures past it are no longer significant. i think this will be the answer that your teacher is after, but it may not be.

another way to look at uncertainty is to calculate the farthest possible outliers* half of the difference of the outliers will be your uncertainty value.
*in this case, the highest concentration is if the balance measured too much salt and the flask was a little too small, giving .101 g of NaCl and .99 ml, giving .102 g/L. the lowest would be the opposite happening, giving .98 g/L

i am not sure how clear my explanation was, but i hope this helps!