Question

what happen if calcium carbonate+sodium hydroxide mix?

Answer 1

The product of reaction between calcium carbonate and sodium hydroxide is calcium hydroxide and sodium carbonate. The process for this reaction is:

$$\mathrm{CaCO_3(s)} + 2\mathrm{NaOH_{(aq)}} \rightarrow \mathrm{Ca(OH)_2(aq)} + \mathrm{Na_2CO_3(aq)}$$

When you heat it later, the water in the solution evaporates leaving you with just the salts.

Also, it is better to say, calcium carbonate is added to sodium hydroxide solution as you add a solid to a solution not really vice versa.