Question

Which of the following does not give flame colouration? (a) \(\mathrm{Mg}\) (b) \(\mathrm{Ca}\) (c) \(\mathrm{Sr}\) (d) \(\mathrm{Ba}\)

Short answer

(a) Mg does not give flame coloration.

Step-by-step solution

Understanding Flame Test

When metal salts are heated, they emit light at specific wavelengths, producing characteristic colors. This is due to the metal ions being excited by the heat and then releasing energy as light when they return to a lower energy state.

List Of Metal Elements

We need to identify the flame colors for the given metals: Magnesium (Mg), Calcium (Ca), Strontium (Sr), and Barium (Ba).

Research Known Flame Colours

Typically, Calcium gives a brick-red flame color, Strontium gives a crimson or red flame color, and Barium gives a yellow-green flame color. Magnesium, however, does not show any characteristic flame coloration in the visible range.

Identifying The Exception

Since Magnesium (Mg) does not show any characteristic flame color when subjected to a flame test, it is the metal that does not give flame coloration.

Key concepts

Metal Salts

When we talk about metal salts in the context of flame tests, we're focusing on how different metal ions behave when heated. The salt part typically refers to the ionic compound formed between metal cations and non-metal anions. When these salts are subjected to heat, such as in a Bunsen burner flame, the metal ions within them can be energetically excited.
Metal salts have a variety of applications due to their interesting properties. Here are some important things to keep in mind:

• When the metal ion in a salt is heated, it absorbs energy. The electrons in the metal ions jump to higher energy levels temporarily.
• Once the electrons return to their normal state (ground state), they release energy in the form of light.
• This released light corresponds to specific wavelengths that are unique to each metal, resulting in different colors being visible to the human eye.

These unique flame colors make metal salts useful for demonstrations in chemistry education and even in creating colorful fireworks.

Characteristic Colors

The characteristic colors observed during a flame test are due to the specific electron transitions that occur within each metal ion. Different metals emit different colors, which allows us to identify them using just a flame test. This is a simple yet powerful form of analysis.
Here's some additional insight:

• Calcium salts emit a brick-red color, showcasing electron transitions unique to calcium ions.
• Strontium salts produce a crimson or intense red flame, which clearly distinguishes strontium ions from others.
• Barium salts emit a yellow-green color, which is quite distinctive and easy to recognize.

These characteristic colors act like a fingerprint for each metal, helping scientists and students alike to determine the metal present in various substances. However, not all metals will always show a prominent coloration; for example, magnesium lacks a visible flame color, which can sometimes make identification trickier.

Emission Spectra

At the core of flame tests and the characteristic colors emitted are emission spectra. Emission spectra are a graphical way of showing how much light at different wavelengths a substance emits. This is particularly useful in identifying materials based on the light they emit.
Let's break down some key points:

• When a metal ion is heated, its electrons are excited to higher states and then fall back to lower states. This process releases energy as light.
• Each metal has a unique emission spectrum, which appears as distinct colored lines. These lines are called spectral lines and are specific to each element.
• This forms the basis for spectral analysis, a method used by scientists to understand and identify composition not just of earth-bound substances, but of distant stars and galaxies too.

Thus, understanding emission spectra not only helps in identifying metals in simple flame tests but is also a fundamental principle in astrophysics and various fields of chemistry.