2. A calibration plot of absorbance vs. concentration was obtained, with the slo

Question

2. A calibration plot of absorbance vs. concentration was obtained, with the slope of the line as 1220 M-. The absorbance concentration of the dilute aspirin solution? of a dilute aspirin solution mixed with FeCl, was 0.72. What is the aliquot of concentrated aspirin Brand X solution was diluted to a final volume of 100 mL s solution's concentration was determined to be 5.5 × 10-5 M. what is the concentra- with FeCl,. Thi tion of the aspirin in the original aspirin Brand X solution? 9 Analys Prelab Questions: Determination of Aspirin by Spectrophotometric

Explanation / Answer

We must apply Beer’s Law

A = e*l*C

A = absorbance of sample

e is the molar absorptivity , the typical units are 1/M-cm

l size of cuvette, typically reported in cm

c is the molar concentration, in mol per ltier or M

for the "slope" assume

A = slope*C

A = 1220 * C

substitute A

0.72 = 1220 * C

C = 0.72/1220

C = 0.00059 mol per liter

Q3

a

We need to apply dilution law, which is based on the mass conservation principle

initial mass = final mass

this apply for moles as weel ( if there is no reaction, which is the case )

mol of A initially = mol of A finally

or, for this case

moles of A in stock = moles of A in diluted solution

Recall that

mol of A = Molarity of A * Volume of A

then

moles of A in stock = moles of A in diluted solution

Molarity of A in stock * Volume of A in stock = Molarity of A in diluted solution* Volume of A in diluted solution

Now, substitute known data

M1*V1 = M2V2

5*C1 = 100*(5.5*10^-5)

C1 = 100/5*(5.5*10^-5)

C = 0.0011 M

Q3b

mmol of NaOH = MV = 10*1 = 10 mmol

mmol of aspirin = 10 mmol

mass = mmol*MW = (10*10^-3)(180) = 1.8 grams of aspirin; 1800 mg

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