3. Pure water is carbonated by means of bubbling gaseous CO2 through it. Then it

Question

3. Pure water is carbonated by means of bubbling gaseous CO2 through it. Then it is bottled. If the air space in the bottle above the water contains only CO, at a pressure of 2 atm, what is a. pH of the carbonated water? Use an exact solution. (assume T 25°C) (3 marks) Solve part (a) using simplifying assumptions. Check the assumptions. (3 marks) b. 1 Note: Overall presentation grades are provided for adequate citations, references, proper use of units, neatness and organization. The bottle is opened, and the water is poured into a glass. Assume that the surrounding atmosphere is unpolluted at T 25°C. What is the new equilibrium pH? (Hint: You should not need to do any new calculations for this, but justify your answer). In terms of the concentration of dissolved CO2 species (H2CO,*, HCO;, CO,), describe the changes that take place as the new equilibrium is approached (increase or decrease) (3 marks) c. Carry out this experiment: Pour a carbonated beverage (soda or carbonated water, coke, 7-UP, beer etc.) into a glass and then sprinkle some salt into the beverage. Describe and explain what you have observed. Does the addition of a small amount of salt influence the equilibrium pH? Does it influence the rate of approach to equilibrium? What is the role of the salt? (3 marks)

Explanation / Answer

Here we must use the henry´s law, the henry constant for CO2 is 0.034 M / atm

concentration = K * pressure

c = 0.034 M / atm * atm

c = 2 * 0.034 = 0.068 M

For the second part the reaction is

CO2 + H2O (l) ----> H+ + HCO3-; we will also need the value of Ka which I have with a value of 4.4 x 10-7

Ka = HCO3 * H+ / CO2

at equilibrium HCO3 has the same ammount than H+

Ka = x2 / CO2

x2 = Ka * CO2

4.47 x 10-7 = x2 / 0.068

x2 = 3.04 x 10-8

x = 0.000174 = H (assuming we have an equilibrium)

PH = -log (H) = -log(0.000174) = 3.758

*Just 1 question at a time please =)

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