1. If the crystal water in Na2CO3 is not completely removed, the actual concentration of Na2CO3 will be low, and the HCL volume consumed by titration will be reduced, resulting in a higher calculation result of HCL concentration.

2. Use a pipette, because it is a reference object, so it requires accuracy, and the measuring cylinder is not accurate enough.

3. The conical flask does not need to be dried, because it is the reference substance Na2CO3 that really participates in titration.