Question

Number of metal ions characterized by flame test among the following is _______.
$\text{Sr}^{2+}, \text{Ba}^{2+}, \text{Ca}^{2+}, \text{Cu}^{2+}, \text{Zn}^{2+}, \text{Co}^{2+}, \text{Fe}^{2+}$

Answer 1

Correct Answer: 4

To determine the number of metal ions that can be characterized by a flame test, we need to know which of the given ions produce characteristic colors upon heating in a flame.

Analysis of Each Metal Ion:

• Sr²⁺: Produces a bright red flame.
• Ba²⁺: Produces a green flame.
• Ca²⁺: Produces an orange-red flame.
• Cu²⁺: Produces a blue-green flame.
• Zn²⁺: Typically does not produce a distinct color in a flame test.
• Co²⁺: Produces a blue flame.
• Fe²⁺: Produces a yellow-green flame, but is less distinctive and often masked by other colors.

Summary of Metal Ions with Characteristic Flames: Characteristic colors are seen with Sr²⁺, Ba²⁺, Ca²⁺, Cu²⁺.

Counting those that yield distinct flame colors: Sr²⁺, Ba²⁺, Ca²⁺, Cu²⁺

Thus, the total number of metal ions characterized by flame tests from the list is: 4

Answer 2

Determine how many of the given metal ions can be characterized (identified) by a flame test.

Concept Used:

The flame test is used to identify certain metal ions based on the characteristic color they impart to a flame. This occurs when heat excites the metal ions' electrons to higher energy levels; as they fall back, they emit light of specific wavelengths. Not all metal ions produce a characteristic flame color that is useful for identification.

Step-by-Step Solution:

Step 1: List the characteristic flame colors for common metal ions:

• Strontium (Sr²⁺): Crimson red
• Barium (Ba²⁺): Apple green
• Calcium (Ca²⁺): Brick red
• Copper (Cu²⁺): Blue-green (often with flashes of other colors)

Step 2: Analyze Sr²⁺. It gives a characteristic crimson red flame. Yes, characterized by flame test.

Step 3: Analyze Ba²⁺. It gives a characteristic apple green flame. Yes, characterized by flame test.

Step 4: Analyze Ca²⁺. It gives a characteristic brick red flame. Yes, characterized by flame test.

Step 5: Analyze Cu²⁺. It gives a characteristic blue-green flame. Yes, characterized by flame test.

Step 6: Analyze Zn²⁺. It does not give a characteristic flame color that is useful for identification. No.

Step 7: Analyze Co²⁺. It does not give a characteristic flame color that is useful for identification. No.

Step 8: Analyze Fe²⁺. It does not give a characteristic flame color that is useful for identification. No.

Thus, the metal ions characterized by flame test are: Sr²⁺, Ba²⁺, Ca²⁺, and Cu²⁺.

The number of metal ions characterized by flame test among the given list is 4.