Chemical X is a weak base that has a pH range of 7-9 after it reaches equilibriu

Question

Chemical X is a weak base that has a pH range of 7-9 after it reaches equilibrium. A certain solution of chemical X has a pH of 8.10 at 25 degree C but the same chemical will have a pH of 7.80 at 37 degree C. a. Write the chemical reaction of chemical X behaving like a base in water b. What product is made when Chemical X reacts with water? How would that effect the pH? Would the product make the pH more acidic or basic in nature? c. Note that the pH chances from 8.10 at one temperature, to 7.80 at a higher temperature. Explain, from a chemical perspective why the pH changes with temperature, what is happening in solution to cause this?

Explanation / Answer

Ans. A. A weak base forms hydroxyl ions from water molecules when dissolved in it.

            X + H2O --------> XH+ + OH-

The resulting increased OH- makes the pH alkaline (pH rises above 7.0)

B. The product of this reaction of protonated cation of the base (XH+) and hydroxyl ions (OH-). Formation of OH ions makes the solution basic or alkaline.

C. pH at 250C = 8.10

pH at 370C = 7.80

Le Chatelier’s principle states “if a dynamic equilibrium is disturbed by changing the conditions (Concentration, Volume, Pressure, temperature, etc.), the position of equilibrium shifts to counteract the change to reestablish an equilibrium”.

As pH decrease on increasing temperature, [OH-] also decreases with increase in temperature.

Thus, increase in temperature shifts the equilibrium to the left (backward direction), that favors the formation base as follows-

                        XH+ + OH- ------> X + H2O

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