Answer to Question #96244 in General Chemistry for Peter Adu Tutu

Question

is an identification of pH solution by using indicator paper. In acid solution it becomes red, in alkaline solution – deep blue and in distilled water – no change is happening. My question is

1. I need reasons for using the above
procedure

2. And how it can be demonstrated that all the reactant in a neutralization reaction have been used

Answer 1

1) to determine the pH of the medium using a universal indicator. It is wetted with a solution for which it is necessary to determine the pH.

In an acidic environment, there is an excess of Hydrogen-H cations, which change the color of the indicator to red (or its shades). In an alkaline environment, there is an excess of hydroxyl group anions - OH, which stain the indicator paper in a dark blue color. In a neutral environment, the concentrations of these ions are equal, there is no excessive amount of either Hydrogen cations or anions of the hydroxyl group, so the color will be green.

2) from the first paragraph it follows that if there is no excess of any of the ions that can color the indicator red or dark blue, the ions will be in equilibrium or formally absent in the solution, and then it is necessary to use the indicator to prove the presence of a neutral medium. It will change its color to green.