✔ 最佳答案
1. An acid is a substance which, when dissolved in water, give H+ as the only positive ion. This is the definition of acid.
2. An alkali is a soluble base, A base in turn means a substance which react with acid to give salt and water as the only products.
3. carbonates are alkaline but they are not alkali (read the definition above !) actually aqueous carbonates do have some OH- ions (AL Level) by the following reversible reaction:
[CO3]2- + H2O <==> [HCO3]- + OH-
4. MgSO4 is an acidic solution but not an acid. In CE level just remember than a salt formed from weak base and strong acid has an acidic aqueous solution. In AL, this can be explained by the equation:
[Mg(H2O)6]2+ + H2O <==> [Mg(OH)(H2O)5]+ + H3O+
5. indicators are dye which are sensitive to pH change. Actually this is beyond CE, indicator are usually organic compound which chages structure when put in different pH environment.