Question

If you can measure masses to +- 0.0001g in this experiment (e.g., let us say that your sample mass is 0.1149g), and you know that your volumetric pipet measures exactly 25ml and the molar mass of Al(Ox)3 is 459.42g/mol, to how many significant figures should [Al3+] results be reported?

For example, if the calculated [Al3+] is determined to be exactly 0.1M, how would you report this value using the correct number of significant figures?

Al3+ (aq) + 3Ox- (aq) ------> AlOx3 (s)

Answer 1

0.0001 --> significant figures --> 0.1149 g

no of significant figues --> 4 (1,1,4, and 9)

assume we are not using larger numbers, i.e. 1.1149 g, then, we will have to calculate 5 sig. fig

if V = 25 mL exactly, then this has no effect at all in significant figues, that is, we coud consider 25.00000 infinte

so then, only the mass measuring device is limiting for now....

the total molecular mass --> 459.42 g/mol --> 5 significant figures (4,5,9,4,2)

the Molarity is exact, so onea gain, it is also infinite precise 1.0000.... to infinity

then

the least significant number is the previous 4 significant figures

note that stoichiometric factors are also exact/precise, so they are accoutned with infinite significant figures

the limiting sig. fig number is the mass

so the answer must not go furhter than 4 significant figues