Answer 39.78% Explanation The analysis done by standard addition method The form
ID: 699480 • Letter: A
Question
Answer
39.78%
Explanation
The analysis done by standard addition method
The formula for standard addition method is
Cx /(Cx + Ca) = Sx/Sx+a
where,
Cx = Unknwon Concentration , X
Ca= added concentration , 0.035M Cu solution is 12.5time diluted in reading solution ,so, added concentration is 0.0028M
Sx = Sample signal, 0.1931 Absorbance
Sx+a = Signal for sample + added Concentration, 0.5272 Absorbance
Therefore,
X/(X + 0.0028M) = 0.1931 /0.5272
X/(X + 0.0028M ) = 0.3663
X = 0.3663X + 0.00103M
0.6337X = 0.00103M
X = 0.001625M
Unknown concentration in reading solution = 0.001625M
reading unknown solution is 10 time diluted
therefore,
Concentration in original stock solution = 10× 0.001625M = 0.01625M = 0.01625mol/L
No of mole of Cu in 500ml of stock solution = 0.008125mole
Molar mass of Cu = 63.55g/mol
mass of Cu = 63.55g/mol × 0.008125mol = 0.5163g
sample weight = 1.298g
percent of Copper in the ore sample = 0.5163g/1.298g = 39.78%
Explanation / Answer
III. Problem Solving/Calculations (64 points, You must show your work) 1. (10) A sample of copper is to be determined using UV-Vis absorption analysis. A 1.298 g sample of a copper ore is crushed, digested in 3M HNO3, and then diluted to 500.0 mL in a volumetric flask The analysis condition and results are listed in the following table. Calculate the percent of copper in the ore sample. mL. Stock solution mL 0.035M Cu standard solution Final volume (mL) 100.0 10.00 10.00 0.00 8.00 64.1 29.7 100.0