to stay in Protected w CHM 131 Laboratory Study Questions Reaction Rate of Pheno

Question

to stay in Protected w CHM 131 Laboratory Study Questions Reaction Rate of Phenolphthalein Decomposition. Name: Section: These questions are to be turned in at the beginning of lab, Show your work where appropriate! 1. If you mix two solutions, 25.0 ml of 0.231 M NaCl and 33.1 ml of 0.161 M NaOH, calculate the final sodium, chloride and hydroxide ion concentrations. 2. Using a first order rate law below, calculate the concentration of [A] after 20 minutes if the initial [Ao] concentration was 0.5 M and the rate constant was 5.1x10s (Note: you will need the integrated form of this equation.) Rate dlAL

Explanation / Answer

NaCl = 25.0ml of 0.231M

NaOH= 33.1ml of 0.161M

Total volume= 25.0+33.1= 58.1 ml

after mixing two solutionns

[NaCl] = 25.0x0.231/58.1= 0.099 M

NaCl-------------- Na+ + Cl-

concentration of Na+ = 0.099M

concnetration of Cl-= 0.099M

[NaOH]= 0.161Mx33.1ml/58.1= 0.0917M

NaOH--------------- Na+ + OH-

[Na+]= 0.0971M

[OH-] = 0.0917M

Total concentrationn of Na+ = 0.099+0.0917 =0.1907M

b)

Initial concentration= [A]0= 0.5M

rate constant=5.1x10^-4s-1

t= 20 min= 20x60 = 1200 sec

for first order reaction

K= 2.303/t log[A]0/[A]t

5.1x10^-4 = 2.303/1200 xlog(0.5)/[A]t

[A]t= 0.271M

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