In the past years, there has been intense scrutiny of the tabacco industry. One

Question

In the past years, there has been intense scrutiny of the tabacco industry. One specific charge is that cigarette manufacturers have manipulated tobacco chemically to make the cigarettes more addictive. The component in cigarettes that causes physical addiction is nicotine. Nicotine occurs in two forms:

The acidic form is not volatile and cannot be taken up into the body from cigarette smoke. The free base form is volatile and is easily taken up through the lungs from cigarette smoke. (Note: the term "free basing" comes from adding a base to a drug to make it volatile so that it can be smoked.) The charge against cigarette manufacturers is that ammonia (a base) is added to change the form of the nicotine to make it absorbable. Given the equation nicotine H+ ---> nicotine + H+, pKa=8.0, answer the following questions (ignore the fact that nicotine is volatile).

(a) Calculate delta G

Explanation / Answer

a) pka = 8 , Ka = 10^-8

NicH+ ---------> Nic + H+ , Nic = nicotine ,

Ka = [Nic][H+][NicH+] = 10^-8

dGo = -RT ln K = -8.314 x 298 ln ( 10^-8) = 45639 J/mol = 45.64 KJ/mol

b) T = 60C = 60+273 = 333 K , dGo = -8.314 x333 x ln ( 10^-8) = 50998 J/mol = 51 KJ/mol

c) pH = pka + log [NIc]/[NicH+]

5 = 8 + log [Nic]/[NicH+]

[Nic]/[NicH+] = 0.001

at pH = 6

6 = 8 + log [Nic]/[NicH+]

[Nic]/[NicH+] = 0.01

at pH = 7

[Nic]/[NicH+] = 0.1

at pH = 8

[Nic]/[NicH+] = 1

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