How can a scientist help a colleague perform a better experiment?
Tell him/her to do it again?
Most senior professors and researchers do not tend to spend a lot of time on the bench. Of course, they have served their apprenticeship, but their days would be full of undergraduate teaching, administration, review, and policy. Nevertheless, in a practical discipline such as chemistry a senior prof is very likely to have a long and distinguished history on a laboratory bench.
The senior researcher can examine the experiment and test assumptions and conclusions. What is the student trying to do? What is the student doing? (These questions do not have the same answers!). Is there an assumption the student is making? Is there a better experiment to perform?
And of course, a prof or senior colleague can act as a sounding board. If something is not working, there is a better way, and an alternative approach.