To determine the rate of reaction for the decomposition of aspirin a student wei

Question

To determine the rate of reaction for the decomposition of aspirin a student weighted out 0.0650 g of aspirin (MW = 180.57 g/mol) and transferred it to a test tube. In the test tube he added 1.00 mL of n-propanol and 10.00 mL water. The test tube with the mixture aspirin was first heated in the water bath at 92 degree C for 6 minutes and after removed from the bath and cooled down. To determine minutes the amount of salicylic acid obtained in the aspirin degradation, first, 5.00 mL of 0.025 M Fe(NO_3)_3 was added to obtain the violet complex of iron-salicylate and second the absorbance of the violet solution was measured at 525 nm with a S-20 spectrometer and found to be 0.304. a) What is the molarity of the aspirin solution prepared, before being heated to 92 degree C? Concentration of aspirin in test tube before reaction = ___ mol/L. B. Standard stock solution of salicylic acid is prepared by dissolving 0.0799 g of salicylic acid (MW = 138.12 g/mol) in water and diluting to 50.00 mL. ______ a) what is the concentration of salicylic acid in the stock solution express in mol/L? Concentration of salicylic acid in stock solution ____ mol/L C. The following standard salicylic acid solutions (2.31 times 10^-4; 4.63 times 10^-4; 6.94 times 10^-4; 9.26 times 10^-4 and 11.6 times 10 mol/mL) were prepared from the stock solution (each standard solution was prepared in an amount of 10.00 mL). The absorbance of the standard solutions is obtained from the S-20 spectrometer at the wavelength of 525 nm as shown in the data table below: A calibration curve was prepared by plotting Absorbance vs. Concentration and the plot is: a) Complete the data table on the previous page. b) Describe the method that will be used to make the Standard Solution 2, specifying what device will be used and how. a) Using the calibration equation, what is the concentration of the salicylic acid obtained by degrading the aspirin (test tube) in part (A) on the previous page? Concentration of the salicylic acid in test tube = ____ mol/L D. Calculate the rate of reaction for the aspirin degradation at 92 degree C using the following equation: Rate of reaction = delta [Sal]/delta t Rate of reaction = ___mol/L middot s

Explanation / Answer

A) a)molarity of aspirin solution=moles of aspirin/total volume of solution

moles of aspirin=mass/MW=0.0650g/180.57g=3.6*10^-4 moles

molarity=3.6*10^-4 moles/(11ml*10^-3L/ml)=0.0327 mol/L

B)concetration of salicyclic acid in stock solution=moles of aspirin/total volume of solution

moles of aspirin=mass/MW=0.0799g/180.57g=4.425*10^-4 moles

concetration of salicyclic acid in stock solution=4.425*10^-4 moles/(50ml*10^-3L/ml)=0.00885 mol/L

or, answer is 0.00885mol/L

C)bA)std solution2 are prepared by dilution of stock solution

concentration of salicylic acid in std sol=C(std)*V(std) [V=volume of std solution]

then C(stock)*V(stock)=C(std)*V(std)

or,C(std)=C(stock)*V(stock)/V(std)

a) V(stock))=C(std)*V(std)/C(stock)

so in the table,std solution 1, V(stock)=C(stock)*V(stock)/C(std)

=[2.31*10^-4 mol/L *(10ml*10^-3L/ml)]/.00885mol/L=0.000261 L=0.261 ml

c)Absorbance=0.304

So,from the callibration curve,the corresponding conc of salicylic acid=0.000102mol/L

rate of rxn =dsal/dt=initial conc-final conc/time=0.0327 mol/L-0.000102mol/L/6min=0.00528M/min=0.00528M/60s=8.8*10^-5 M/s

Related Questions

Navigate

• Browse (All)
• Browse T
• Subjects

---

---

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