The experiment is said to be
valid if the conclusion of the experiment leads to one and only conclusion, i.e. the only thing that will affect your result is your independent variable. Therefore, you need to discuss what variables you controlled in your experiment, for example: concentration and volume of standard solution, temperature, etc.
Dreamerish*~ said:
Validity - Correct use of equipment. Did you blow out the last drop of solution from the pipette? Did you leave the filter funnel in the burette while titrating? Did you clean the equipment appropriately? Do you understand the concept of the equivalence point well enough to know when to stop? And so on.
I think this is more about
accuracy than validity.
A valid experiment may NOT be accurate, but an accurate experiment must be valid.