O Timer Notes d Evaluate Feedback Print info Course Contents CHEM 105 Lab 11 Pos

Question

O Timer Notes d Evaluate Feedback Print info Course Contents CHEM 105 Lab 11 PostLab 11 Note: to use scientific notation, enter 2.6 16 as 2.6e16 Question #1 Here are your data for the known salicylic acid solutions. Absorbance Concentration (M) .75 Dilution #1 5.000e-4 M Dilution #2 .55 3.750e-4 M 2.500e-4 M Dilution #3 .39 Dilution #4 1.250e-4 M 21 Construct a plot of absorbance (y-axis) versus concentration (x-axis) from the data above. Determine the slope of the best-fit line. Make sure to force the best fit straight line through the origin. Excel has an option to do this (instructions for Excel 2013 on Windows, instructions for Excel 2011 on Mac). The molar absorptivity constant is 1.5x103 Your results are now shown above. Question #2 Here are your data for the recrystallized aspirin sample solutions. Mass Absorbance Recrystallized sample .3980 g 06 Part 1:

Explanation / Answer

A = e*l*C

choose any point to find out "l"

0.75 = (1.5*10^3)*l*(5*10^-4)

l = 0.75 /( (1.5*10^3)*(5*10^-4)) = 1

so

for A = 0.06

assume

0.06 = (1.5*10^3)(1)*C

C = 0.06/((1.5*10^3)(1)) = 4*10^-5 M (which is PART 1)

PART 2

.V = 250 mL of soln. find mass

mol = MV = (4*10^-5)(0.25) = 10^-5 mol of acid

MW of salicylic acid = 138.121 g/mol

so

mass = mol*MW = (10^-5)(138.121 ) = 0.00138 g of acid

Part #

% mass = mass of s.acid / sample ¨100 %= 0.00138 /0.3980 * 100 = 0.346733 % is S.Acid

Related Questions

Navigate

• Browse (All)
• Browse O
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.