Question

**1. ** A student used standard solutions of aspirin in a FeCl_{3}-KCl-HCl mixture to plot

a graph of molarity versus absorbance for diluted aspirin solutions of known concentration. The student determined the slope of the graph to be** 4,966** M^{-1}cm^{-1}. Next the student measured out **0.29 **grams of a headache medicine tablet and dissolved it in 10.0 ml of NaOHand then added enough water to make a 100 ml solution. Five ml of this solution was then added to another 100 ml flask and diluted to the mark with enough FeCl_{3}-KCl-HClmixture. The solution was then measured for** absorbency as 0.326. **Calculate the **original molarity (Mo)** of the aspirin solution using the dilution equation. *(Put your answer in 3 significant figures)*

**2. ** A student used standard solutions of aspirin in a FeCl_{3}-KCl-HCl mixture to plot a graph of molarity versus absorbance for diluted aspirin solutions of known concentration. The student determined the slope of the graph to be** 4,741** M^{-1}cm^{-1}. Next the student measured out **0.236 **grams of a headache medicine tablet and dissolved it in 10.0 ml of NaOH and then added enough water to make a 100 ml solution. Five ml of this solution was then added to another 100 ml flask and diluted to the mark with enough FeCl_{3}-KCl-HCl mixture. The solution was then measured for** absorbance as 0.311. **Calculate the** percent pure acetylsalicylic acid** in the sample of headache medicine. *Put your answer in 3 significant figures.*

**3.** Why the wavelength of 530 nm was used? *(Choose all that apply)*

A.This wavelength corresponds to the color purple.

B.This wavelength corresponds to the color of the solution.

C.This wavelength corresponds to the complimentary color of the solution.

D.This is the wavelength that gives the maximum absorbency readings.

E.This wavelength corresponds to the color yellow.

**4. ** What is the purpose of the sodium hydroxide used in the reaction? *(Choose all that apply)*

A.to help neutralize the reaction so it is basic

B.to react with the salicylate ion

C.to hydrolyze the aspirin to form the salicylate ion.

D.to produce the salicylate ion

E.to produce acetic anyhydride

**5. ** If a student fails to wipe his/her fingerprints from the cuvette prior to measuring the absorbance, how this will affect the reading? *(Choose all that apply)*

A.the absorbance readings will not be affected by the smudges.

B.the spectrophotometer will read the absorbancy as high, since the transmittance will be low.

C.the absorbance will be higher because more light will be absorbed by the sample

D.The smudges will block the light entering the sample and the absorbance will read higher.

E.The absorbance will read lower because less light will be allowed to transmit through the sample.

F.the smudges will reduce the concentration of the sample and the absorbance will read lower

**6. ** Why is it important to use the same cuvette throughout the experiment? *(Choose all that apply)*

A.so that any scratches in the glass cuvette will be read the same way for all samples

B.as long as the cuvette is from the same box, you can use more than one cuvette to save time

C.to ensure that you do not introduce a contaminant into your sample

D.because the lab has only a few cuvettes for all the students to use and we must be conservative

E.to reduce the number of variables in the experiment

**7. ** A student used standard solutions of aspirin in a FeCl_{3}-KCl-HCl mixture to plot a graph of molarity versus absorbance for diluted aspirin solutions of known concentration. The student determined the slope of the graph to be** 4,777** M^{-1}cm^{-1}. Next the student measured out **0.276 **grams of a headache medicine tablet and dissolved it in 10.0 ml of NaOH and then added enough water to make a 100 ml solution. Five ml of this solution was then added to another 100 ml flask and diluted to the mark with enough FeCl_{3}-KCl-HCl mixture. The solution was then measured for** absorbance as 0.302 Calculate the molarity of the diluted solution** determined from the absorbency and the slope. *Round your answer to 3 significant figures*

**8. ** A student used standard solutions of aspirin in a FeCl_{3}-KCl-HCl mixture to plot a graph of molarity versus absorbance for diluted aspirin solutions of known concentration. The student determined the slope of the graph to be** 4,246** M^{-1}cm^{-1}. Next the student measured out **0.251 **grams of a headache medicine tablet and dissolved it in 10.0 ml of NaOH and then added enough water to make a 100 ml solution. Five ml of this solution was then added to another 100 ml flask and diluted to the mark with enough FeCl_{3}-KCl-HCl mixture. The solution was then measured for** ****absorbency**** as 0.34. **Calculate the molarity of the diluted solution determined from the absorbency and the slope. Then use the molarity of the original solution, its volume and molar mass to **calculate the grams of pure acetylsalicylic acid. ***Put your answer in 3 significant figures.*