Question

What is the nature of solution at $60{}^\circ C$ whose pH is 6.7?
  (A) Basic
  (B) acidic
  (C) neutral
  (D) none

Answer 1

Hint: Solutions can be acidic, basic or neutral depending on the pH of the solution. On the pH measurements temperature plays a significant role. All solutions will experience a variation in their pH value over the changes in temperature.

Complete Answer:
-As we know, pH is an indication of the hydrogen ion concentration. In mathematical terms it’s the negative logarithm of the hydrogen ion concentration (${{H}^{+}}$).
-At pH 7, the solution is at a neutral position which means that the concentration of ${{H}^{+}}$ and $O{{H}^{-}}$ ion is the same. From the range 7 to 14, a solution is basic. The pOH should be observed in the perspective of $O{{H}^{-}}$ instead of ${{H}^{+}}$. In a basic solution there are more $O{{H}^{-}}$than ${{H}^{+}}$ in the solution.
- From the pH range 1 to 7, a solution is said to be acidic. Or in other words when the value of pH is less than 7, it is considered acidic. Here there are more ${{H}^{+}}$ than $O{{H}^{-}}$ in the solution.
-Every solution will experience a change in their pH value through changes in temperature. The reason is that as the temperature increases, molecular vibrations will increase which results in the ability of water to ionize and form more hydrogen ions and as a result, the pH will drop.
- From the above discussions it is clear that the nature of solution at $60{}^\circ C$ whose pH is 6.7 will be acidic.

Therefore the answer is option (B) acidic.

Note: It should be noted that even if the pH of a solution falls as temperature increases, this does not mean that solution becomes more acidic in all conditions. A solution will be acidic only if there is an excess of hydrogen ions over hydroxide ions (i.e., pH < pOH) and in the case of pure water, there will be always the same concentration of hydroxide ions and hydrogen ions and therefore, the water is still neutral (pH = pOH) even if its pH changes.