(1) Since steam distillation allows organic matter to be distilled out of the mixture at a lower temperature, it can avoid losses caused by distillation under normal pressure and improve the efficiency of separation and purification. At the same time, the operation and equipment are simpler than vacuum distillation, so steam distillation can be used to separate and purify organic matter.

So the answer is: in order to steam out benzaldehyde;

(2) In the cinnamic acid preparation experiment, slowly adding solid sodium carbonate can reduce the carbon dioxide production rate and help adjust the pH. Therefore, the reason for slowly adding solid sodium carbonate to adjust the pH value is: if the sodium carbonate is added too fast, It is easy to generate a large amount of CO 2 bubbles, and it is not conducive to accurately adjusting the pH value.

So the answer is: If the sodium carbonate is added too fast, a large amount of CO 2 bubbles are easy to be generated, and it is not conducive to accurate pH adjustment. value;

(3) Since washing is to wash away impurities on the solid surface, the solubility of solids in cold water decreases, which can reduce solid loss.

So the answer is: purify, wash away Impurity ions on the surface of the solid, while using cold water is to reduce the loss caused by dissolution of the solid;

(4) 2C 6 H 5 CHO KOH (concentrated) → C 6 H 5 COOK C 6 H 5 CH In the 2 OH reaction, the aldehyde group is oxidized to a carboxyl group, and at the same time the aldehyde group is reduced to an alcoholic hydroxyl group, which is a redox reaction.

So the answer is: redox reaction;

( 5) According to the reaction C 6 H 5 CHO (CH 3 CO) 2 O? C 6 H 5 CH=CHCOOH CH 3 COOH, benzaldehyde and propionic anhydride [(CH 3 CH 2 CO) 2 O] in anhydrous K 2 CO The reaction equation in the presence of 3 is: ,

So the answer is: .