Question

In an experiment a student dipped pH papers in four different solutions A, B, C and D and reported his observation as given below:

Solution	A	B	C	D
Colour of pH paper	Light green	Blue	Green	Red

1. In which one of these solutions is the concentration of
   1. hydrogen/hydronium ions;
   2. hydroxyl ions maximum?
2. Give one example each of the two solutions identified in (i) above.
3. What would be the pH of the resultant mixture obtained when these two solutions are mixed together in equal proportions? Justify your answer.

Answer 1

1. The food chain shows a unidirectional flow of energy, whereby energy from the sun is transferred to producers, then to primary consumers, followed by secondary and tertiary consumers, with energy released as heat at each stage. This lost energy never returns to its previous level because the primary source of energy is the sun, and once energy is used by an organism, it cannot be recycled back to the sun for utilization.
2. Solution D (red color) signifies a high concentration of hydrogen ions, as observed in hydrochloric acid (HCl). Solution B (blue in color) signifies a high hydroxyl ion concentration, similar to that found in sodium hydroxide (NaOH).
3. When an acidic solution (D) and a basic solution (B) are combined in equal proportions, they will neutralise each other, producing a salt and water. The resulting pH will be around 7 (neutral) since both solutions possess equal strength.
   \[\ce{HCl + NaOH -> NaCl + H2O}\]