Caffeine is a bitter substance that exists naturally in more than 60 plants including coffee beans and tea leaves. There is also synthetic...
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1. Caffeine is a bitter substance that exists naturally in more than

60 plants including coffee beans and tea leaves. There is also synthetic (man-made) caffeine, which is added to some medicines, foods and drinks. For example, some pain relievers, cold medicines and over-the-counter medicines for alertness contain synthetic caffeine. So do energy drinks and "energy-boosting" gums and snacks.
(a) Caffeine from tea can be extracted by using a liquid-liquid extraction technique. If 125 mL of tea solution contains 0.25 M of caffeine is shaken with 75 mL of dichloromethane, 0.55 mmol of caffeine remains in the solution.


i. What is the distribution ratio of caffeine between in tea solution and dichloromethane?


ii. Determine the extraction efficiency of caffeine?


iii. Calculate the total mol of caffeine extracted, if one-time extraction with 60 mL of dichloromethane.


iv. Calculate the total mol of caffeine extracted, if three times extraction with 20 mL of dichloromethane.


v. Briefly explain, the difference in the mol of caffeine extracted in part (iii) and (iv).


(b) An excessive intake of caffeine may cause health problems. Therefore, consumers are towards decaffeinated coffee products. Discuss one (1) method that can be used to remove caffeine from coffee beans.


2. In industry, acids and bases are used in various reactions. Sulfuric acid, one of the most important industrial chemicals, used to manufacture fertilisers for agriculture, make man-made fibers, paints and dyes, and purify petroleum products. The base sodium hydroxide (sometimes called caustic soda) is used for the production of fabrics, paper and cleaning agents. A dominating factor of aqueous equilibrium is the ever-present proton (H+) and hydroxide ion (OH-). Acid-Base theory and equilibria focus on the relationship of these two ions in an aqueous environment.


(a) A sample weighing 0.3325 g contains Na2CO3 was analysed using a titration method. The titration requires 32.5 mL of 0.1000 M HCl standard solution. Calculate the percentage of Na2CO3 in the sample.


(b) Calculate the pH in the titration of 25 mL of 0.3 M hydrofluoric acid with 0.3 M sodium hydroxide after the addition of sodium hydroxide as following volumes. The Ka value is 6.6 x 10-4.


i. 0 mL NaOH
ii. 10.00 mL NaOH
iii. 12.50 mL NaOH
iv. 25.00 mL NaOH
v. 26.00 mL NaOH


(c) If you are planning to perform a titration between ammonia and hydrochloric acid, which indicator that suitable to be used? Give your reason.


3. Redox reaction is typified by any chemical process that involves transfer of electrons between two chemical species is widely used in industrial process.
a) In the manufacture of nitric acid from ammonia, one of the process involves the reaction of nitrogen dioxide with water as shown by the following equation.
2NO2(g) + H2O(l) → H+(aq) + NO3-(aq) + HNO2(aq)


Assign the oxidation state of nitrogen in each of the following.
i. NO2


ii. NO3-


iii. HNO2


b) a balance ionic equation for the oxidation of Mn2+ to MnO4- by S2O82- (in acidic solution).


c) Calculate the concentration of Ag+ in a simple galvanic cell that consist of 0.1M Cu2+ and x concentration of Ag+. The standard electrode potential of Ag+ and Cu2+ are 0.80 V and 0.34 V, respectively. Cell potential (at 25oC) = 0.422V.

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Subject: Chemistry, Science
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