chem question~please help

1. The properties of the chemical required to prepared a standard solution :
- chemical stability over reasonable time
- not photosensitive
- low level of contamination from surrounding (e.g. atmosphere)
- low level of contamination casued by the apparatus that comes into contact with the sample

2.
Avoid of the contamination of the standard solution.
Avoid of the dilution of the standard solution with any moisture on the container.
Avoid of the loss of the standard solution with any solution stick on the surface of the container.

I hope this can help your understanding. :)

In order to be a standard solution, it must maintain standard for prolong period with no special care needed. Necessity to clean the pipette by standard solution is to increase the consumption of standard solution and thus the renewal rate of the standard solution.