METHOD FOR MANAGING ETCHING LIQUID

PROBLEM TO BE SOLVED: To exactly measure the concn. of free acid and to exactly manage this concn. by using a soln. contg. potassium oxalate, oxalic acid and org. acid salt forming a stable complex with ferrous iron ions as a complexing liquid in a method for determining the concn. of the free acid of the etching liquid contg. ferric chloride and managing the same. SOLUTION: The pH of the soln. mixture prepd. by mixing the complexing liquid contg. the potassium oxalate, the oxalic acid and the complexing agent forming the stable complex with Fe and the etching liquid is measured and the concn. of the free acid of the etching liquid is determined. At the time of this mixing, Fe forms potassium iron (III) oxalate which is the stable complex by the reaction of formula II with the potassium oxalate in the complexing liquid. On the other hand, the Fe forms the stable complex by the reaction with the org. acid salt in the complexing liquid. Then, the reaction that the Fe forms the potassium iron (II) oxalate which is the unstable complex by the formula I is suppressed. Approximately the entire amt. of the NaOH is consumed for the purpose of the measurement and the exact measurement is made possible when the measurement is executed by adding the aq. NaOH soln.. to the soln. mixture described above.