The variables were renumbered for the new experimental design, such that the amount of NaOH became x1, the amount of Cu(II) became x2, the reaction temperature became x3, and finally the reaction time became x4.
The variables were renumbered forthe new experimental design, such that the amount of NaOHbecame x1, the amount of Cu(II) became x2, the reactiontemperature became x3, and finally the reaction time becamex4.