Chem acid and alkali

I think you are asking for the symbol "⇌" used in the equation of partial dissociation. The symbol "⇌" represents that the reaction is reversible and finally a state of equilibrium is reach.

For example, consider the partial dissociation of ethanoic acid in dilute aqueous solution:
CH3COOH(aq) ⇌ CH3COO⁻(aq) + H⁺(aq)

In the forward reaction, CH3COOH molecules dissociate to give CH3COO⁻ and H⁺ ions. In the backward reaction, CH3COO⁻ and H⁺ ions associate to give CH3COOH molecules. Finally, a state of equilibrium is reached when the ratio of the ions and the molecules becomes a constant under a fixed temperature.

At the equilibrium state, some of CH3COOH molecules in the aqueous solution dissociate to give CH3COO⁻ and H⁺ ions, but some CH3COOH molecules do not dissociate. It is thus known as "partial dissociation".


1.
(a)
Some colourless bubbles are given off.

(b)
(NH4)2CO3 + 2HCl → 2NH4Cl + H2O+ CO2

(c)
CO3²⁻ + 2H⁺ → H2O + CO2

不好意思!我剛剛再看了一次不明白一個point
你話equilibrium state之後d CH3COOH molecules 又會再dissociate……諗極都唔明!
麻煩你再答一答我。謝謝!

Effervescence

(NH₄)₂CO₃ + 2HCl → 2NH₄Cl + H₂O + CO₂

CO₃²⁻(aq) + 2H⁺(aq) → H₂O(l) + CO₂(g)