Comparison of Methods to Determine the Absence of Copper from Solution: With and Without an Ammonia Test

Abstract

In this research project, two methods were compared to efficiently determine the absence of copper ions from a copper (II) chloride dihydrate (37.274% copper) solution after precipitation using solid magnesium. In one method, a solution color change from teal to colorless was used as indication of a completed precipitation of copper. In the alternative method, ammonia was added to aliquots of solution which indicated remaining copper ions with a royal blue complex. For both methods, magnesium turnings were added to a teal copper (II) chloride solution until it was determined, as indicated above, that all copper had precipitated from solution. Afterwards, any excess magnesium was reacted with concentrated hydrochloric acid. The solution was then filtered and the precipitate was washed, dried, and massed. After ten trials per method, the average percent copper obtained with and without ammonia testing was (34±2)% and (22±2)% respectively with a 95% confidence interval. An F-test indicated an equal variance between methods. The corresponding t-test value was 9.579 compared to the two-tailed t-critical value of 2.101, indicating a statistically significant variation of data between the two methods.