Can sodium carbonate / salt be called basic? 3

[shankerm]

For pH correction of an acidic process, Na2CO3 (Soda ash), is used to neutralise the solution.

Now, my colleage says, Na2CO3 cannot be called basic / alkaline.(since it is a salt)

For example, when you go through the MSDS of SODIUM BI CARBONATE, the pH valve is shown as 8.4. Now, in that case isnt it basic ?

Isnt it understood that a solution form of the salt is being talked about?

Please clarify. Thankyou.

 

[25362]

Ionic compounds, except those with OH^- as the anion, are often called salts by analogy with NaCl.

Both above salts are ionic compounds and considered basic in water solutions.

When bicarb (an amphoteric salt) hydrolyzes it produces more hydroxyls than hydronium ions thus its pH[≈]8.4 (at 25^oC).

The bicarb ion in water reacts as follows:

HCO₃^-(aq) + H₂O(l) <=> H₃O⁺(aq) + CO₃⁼(aq)​

with a K_a2 [&asymp;] 4.8[&times;]10^-11 as an acid, or

HCO₃^-(aq) + H₂O(l) <=> OH^-(aq) + H₂CO₃(aq)​

with a K_b2 [&asymp;] 2.3[&times;]10^-8, as a base.

Since K_b2 > K_a2 (both at 25^oC) the solution should be basic.

When soda ash (the carbonate) dissolves in water
the carbonate ion reacts as follows:

CO₃⁼(aq) + H₂O(l) <=> OH^-(aq) + HCO₃^-(aq)​

with
K_b1 [&asymp;] 2.1[&times;]10^-4

As we see K_b1 > K_b2 and the contribution of hydroxyls comes mainly from the carbonate rather than from the bicarb.

The proportions of bicarb and carbonate ions, as well as the carbonic acid, can be easily estimated given the pH of the solution and viceversa.

 

[bimr]

Sodium Carbonate
A sodium salt of carbonic acid used especially in making glass, soaps and chemicals, in water softening, in cleaning and bleaching, and in photography: as (a) a hygroscopic crystalline anhydrous strongly alkaline salt Na2CO3 (b)Washing Soda.
Source: Merriam-Webster Collegiate Dictionary