PH of neutrality is not exactly 7 (25 °C), although this is a good approximation in most cases. Neutrality is defined as the condition where [H] = [OH] (or the activities are equal). Since self-ionization of water holds the product of these concentration [H]×[OH] = K, it can be seen that at neutrality [H] = [OH] = , or pH = pK/2. pK is approximately 14 but depends on ionic strength and temperature, and so the pH of neutrality does also. Pure water and a solution of NaCl in pure water are both neutral, since dissociation of water produces equal numbers
Dry ice color show is mixed together with the alkali present in the solution, the solution, overall, becomes neutral. HCO + H + NH + OH NH + HCO + HO (addition of ammonia) HCO + H + Na + OH Na + HCO + HO (addition of sodium hydroxide) The color of the solution changes due to the universal indicator, a pH detector. Once the alkali-to-acid universal indicator is incorporated into the solution, the color of the solution changes corresponding to the acidic color of the universal indicator. The color of ammonia and water only is green. However, once the dry ice is