First, she pulverized a tablet of aspirin and separated 23.920 grams of the tabl

Question

First, she pulverized a tablet of aspirin and separated 23.920 grams of the tablet into a 125 mL Erlenmeyer flask. After heating this mass in 5.0 mL of basic solution, she transferred the entire solution into a volumetric flask and diluted it to 100.00 mL. After thorough mixing, she transferred 0.30 mL of this solution into another volumetric flask and diluted it to 10.0 mL. She then measured the absorbance of this diluted solution (D) to be 0.425 (Absorbance is unitless.) With the standard curve in Figure 4 of the experiment, she was able to determine the concentration of aspirin (mM) (x- axis) in the dilute solution. {In case it's difficult to make out, the equation for the curve is y = 0.0129x + 0.014.} y = absorbance = 0.425 x = concentration of aspirin = mM (E) She then used this dilute concentration to "back calculate" the concentration of aspirin in her stock solution (B) using the solution dilution formula. M_stock V_stock = M_dilute V_dilute M_dilute (E) = mM V_dilute (D) = mL M_stock (B) = mM V_stock (C) = mL. Knowing the concentration (B) and volume of the concentrated aspirin solution (B), she was able to calculate the number of moles of aspirin present and convert that to mass (F). moles of aspirin in the solution_stock = moles mass of aspirin in the solution_stock = grams After determining the mass of aspirin in a known mass of tablet. She was able to determine the % aspirin in a tablet. mass of aspirin (F)/mass of tablet (A) times 100 = % aspirin/tablet

Explanation / Answer

a) mass of aspirin tablet = 23.920g

Absorbance = 0.425

Equation for the calibration curve is y=0.0129x + 0.014

So, we have y=0.425 and from this we can calculate x that is concentration of aspirin

concentration of aspirin = 31.8605 mM

This is concentration of aspirin unknown prepared by dilution 0.3mL to 10mL.

b) Now by using dilution formula - Mstock * Vstock = Mdilute * Vdilute, we can calculate the concentration of the stock,

so, concentration (stock) = 10/0.3 * 31.8605 = 1062.02 mM

c) Aspirin tablet was dissolved and treated with 5mL basic solution and diluted to 100mL

therefore, moles of aspirin in 100 mL unknown stock = concentration (stock) * 0.100 L = 1062.02 mM*0.100L = 106.202 mmoles = 0.106202 moles

now calculate the mass of aspirin in the solution(stock) = moles * molar mass = 0.106202 moles * 180 g/mole = 19.11636 g

d) mass of aspirin /mass of tablet *100 = 19.11636 g/23.920 g *100 = 79.92 % aspirin/tablet

Related Questions

Navigate

• Browse (All)
• Browse F
• Subjects

---

---

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