The molecular formula of sodium acetate trihydrate is $C_ {2} H_ {3} NaO_ {2}\ cdot3H_ {2} O $. To clarify its molecular weight, it is necessary to calculate the relative atomic mass of each atom.

The relative atomic mass of carbon ($C $) is about 12, hydrogen ($H $) is about 1, oxygen ($O $) is about 16, and sodium ($Na $) is about 23.

In the molecule of sodium acetate trihydrate, containing 2 carbon atoms, the sum of their relative atomic masses is 2 dollars\ times12 = 24 $; containing 9 hydrogen atoms, the sum is 9 dollars\ times1 = 9 $; containing 5 oxygen atoms, the sum is 5 dollars\ times16 = 80 $; containing 1 sodium atom, the relative atomic mass is 23.

Add the sum of the relative atomic masses of each atom, that is, 24 dollars + 9 + 80 + 23 = 136 $.

Therefore, the molecular weight of sodium acetate trihydrate is 136. This value is crucial in the research and practical application of many chemical fields, such as chemical analysis, solution preparation, etc. Only by accurately grasping its molecular weight can we ensure the accuracy and reliability of experiments and production processes.