Sodium Carbonate is said to be a strong base however when in aqueous solution it doesn't yield OH^- ions so how can we say its a base.
Or do we say its a base because of its PH.
The solution does yeild OH- ions as it is the salt of a strong base and weak acid.
Consider the two equilibria
H2O <-> H+ + OH-...........(1)
H2CO3 <-> 2H+ + (CO3)2-....(2)
when Na2CO3 is added to water it is a salt and totally dissociates to Na+ and (CO3)2- ions.
The carbonate ions then immediately set up the equilibrium in equation (2). This equation lies to the left as I have drawn it, i.e. it is a weak acid and not totally dissociated. So in order to form th un-ionised acid it must remove H+ from the equilibrium in equation (1), and in doing so forces the equilibrium in equation (1) to the right to produce more OH-. Hence the solution contains OH- ions and is highly alkaline.
"Sodium carbonate is said to be a strong base" in the sense that the salt is totally dissociated.
Sodium carbonate (Na2CO3) is indeed considered a strong base, but its behavior in aqueous solution can appear confusing. While it is true that sodium carbonate does not directly yield hydroxide ions (OH^-) when dissolved in water, it does undergo hydrolysis.
Hydrolysis is a chemical reaction where a compound reacts with water to form ions. In the case of sodium carbonate, the molecule reacts with water to produce sodium ions (Na+) and bicarbonate ions (HCO3^-). The bicarbonate ions then react further with water to yield hydroxide ions and carbonic acid (H2CO3), which then dissociates to release more hydroxide ions.
To understand why sodium carbonate is considered a base, we need to look at the behavior of the hydroxide ions produced during hydrolysis. The hydroxide ions increase the concentration of hydroxide (OH^-) ions in the solution and contribute to the alkaline nature of sodium carbonate in water.
Furthermore, the pH of a solution can be used as an indicator of its basic or acidic nature. Sodium carbonate has a pH greater than 7 in aqueous solution, indicating that it is basic.
In summary, sodium carbonate is considered a strong base because it undergoes hydrolysis in water, resulting in the release of hydroxide ions and contributing to the alkaline nature of the solution. Additionally, its pH, which is greater than 7, further supports its classification as a base.