Question

can u plz clear my doubt ..... how sodium hydroxide react with sodium carbonate

Answer 1

Sodium hydroxide cannot react with sodium carbonate because sodium hydroxide is an alkali and sodium carbonate solution is also alkaline as on hydrolysis, it gives carbonic acid (which is weak) and sodium hydroxide (which is a strong base). Moreover, both have sodium ion as cation.

Hope you understand.
A base and a basic salt with the same cation cannot react.

Answer 2

Both compounds are bases so there will not be any reaction between them. About the only thing that happens is that you will get a mixture of sodium carbonate and sodium hydroxide.