find the formula mass and it\'s uncertainty 0.5 g/mL. The uncertainty in the den
ID: 896413 • Letter: F
Question
find the formula mass and it's uncertainty 0.5 g/mL. The uncertainty in the density of water in Table 2-7 is negligible in comparison to the uncertainty in the density of air. We can measure the concentration of HC1 solution by reaction with pure sodium carbonate: 2H^+ + Na2CO3 rightarrow 2Na^+ + H2O + CO2. Complete reaction with 0.967 4 plusminus 0.000 9 g of Na2C03 (FM 105.988 4 plusminus 0.000 7) required 27.35 plusminus 0.04 mL of HC1. Find the formula mass (and its uncertainty) for Na2CO3. Find the molarity of the HCl and its absolute uncertainty. The purity of primary standard Na2CO3 is stated to be 99.95 to 100.05 wt%, which means that it can react with (100.00 plusminus 0.05)% of the theoretical amount of H^+. Recalculate your answer to (b) with this additional uncertainty.Explanation / Answer
(a) Formula mass Na2CO3 = 105.9884 +/- 0.0007 g/mol
that means the values lies between, 105.9891 g/mol and 105.9877 g/mol
(b) moles of Na2CO3 = g/FM
maximum = 0.9674 + 0.0009/105.9891 = 0.009136 mols
minimum = 0.9674 - 0.0009/105.9877 = 0.009119 mols
moles of Na2CO3 = 0.009127 +/- 0.000008 mols
So, moles of HCl will be between : 2 x moles of Na2CO3
= 0.018254 mols
would be 0.018271 mols and 0.018238 mols
moles of HCl with uncertainty = 0.018254 +/- 0.000016
Volume of HCl used,
maximum = 27.35 + 0.04 = 27.39 ml
minimum = 27.35 - 0.04 = 27.31 ml
So, molarity = moles/volume = 0.000667 mM
molarity of HCl = 0.018271/27.39 = 0.000667 M and 0.018238/27.31 = 0.000668 M
Molarity of HCl with uncertainty = 0.0006670 +/- 0.0000005 mM
(c) actual amount of HCl used with 99.5 to 100.05 wt% purity of Na2CO3
moles of HCl with uncertainty = 0.018254 +/- 0.000016
with 100 +/- 0.05% value adjusted : 0.0182791 moles to 0.0181559 mols
0.018254 +/- 0.0000616 mols
Volume of HCl used,
maximum = 27.35 + 0.04 = 27.39 ml
minimum = 27.35 - 0.04 = 27.31 ml
So, molarity = moles/volume = 0.000667 mM
0.018254 +/- 0.0000616
molarity of HCl = 0.0183156/27.39 = 0.000669 M and 0.0181924/27.31 = 0.000666 M
Molarity of HCl with uncertainty = 0.0006670 +/- 0.0000015 mM
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