Question

In the flame test of a mixture of salts, a green flame with blue centre was observed. Which one of the following cations may be present?

• A. \(Cu^{2+}\)
• B. \(Sr^{2+}\)
• C. \(Ba^{2+}\)
• D. \(Ca^{2+}\)

Answer 1

The Correct Option is A

The flame test is a qualitative analysis technique used to detect the presence of certain metal ions based on the color of the flame produced when the substance is heated. Different elements emit characteristic colors when heated in a flame due to the excitation and relaxation of electrons in the metal ions.

In this question, it is mentioned that a green flame with a blue center was observed. Let's analyze which cation corresponds to this observation:

• \(Cu^{2+}\): Copper ions typically produce a green flame with a bluish center during a flame test. This is caused by the emission of light in the visible spectrum when the electrons in copper ions return to their ground state from an excited state.
• \(Sr^{2+}\): Strontium ions produce a bright red flame.
• \(Ba^{2+}\): Barium ions give a pale green flame, but it does not have the characteristic blue center associated with copper.
• \(Ca^{2+}\): Calcium ions result in an orange-red flame.

Based on the color description provided, \(Cu^{2+}\) (Copper ion) is the most likely cation to be present, as it is known for producing a green flame with a blue center.

Thus, the correct answer is \(Cu^{2+}\).