Question

a student separated an unknown mixture of ions using the procedure of part a. when the spots were made visible, a faint spot corresponding to cu2+ was seen. however, the student later learned that the unknown did not contain cu2+. which of the following could cause this result? a. the same spotting capillary was used to spot the cu2+ sample and the unknown sample. b. the cu2+ sample was contaminated with co2+ and fe3+. c. the chromatography paper was not trimmed to the correct dimensions. d. the position of the mobile - phase front was incorrectly marked. explain your answer: ________

Explanation:

Step1: Analyze chromatography error

In chromatography, if the mobile - phase front is not marked correctly, it can lead to misinterpretation of results. But this is not related to the absence of a Cu²⁺ spot.

Step2: Consider sample contamination

If the sample is contaminated with other ions like Co²⁺ and Fe³⁺, it doesn't directly explain the absence of Cu²⁺ in the unknown.

Step3: Check paper preparation

If the chromatography paper is not trimmed to the correct dimensions, it may affect the separation process, but not specifically the presence or absence of a particular ion spot.

Step4: Evaluate spotting process

If the same spotting capillary is used for multiple samples without proper cleaning, cross - contamination can occur. However, since the student found that the unknown did not contain Cu²⁺, it is likely that the sample was not contaminated with Cu²⁺ during spotting. But if the Cu²⁺ sample was contaminated with other substances during the preparation or spotting process that could have affected its detectability or if there was an error in the spotting such that the Cu²⁺ was not properly deposited on the paper for the unknown, it could lead to this result. But the most likely reason among the given options is that the sample was contaminated during the spotting process which could have masked or prevented the detection of Cu²⁺.

Answer:

b. The Cu²⁺ sample was contaminated with Co²⁺ and Fe³⁺.