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In this virtual lab experiment, let us learn the use of flame tests to identify the presence of certain cations in a salt. The aim of the experiment is to perform flame tests and identify the presence of certain cations.
To perform this experiment, the apparatus & material required are sample salts conc.HCl, platinum wire, pencil, watch glass, glass rod, beaker, burner, dropper, cobalt glass.
Students can check the below-mentioned steps to conduct the experiment.
- Step 1: Make a circular loop at the end of the platinum wire using the pencil.
- Step 2: Dip the platinum wire in concentrated hydrochloric acid (HCl), taken in a beaker.
- Step 3: Hold it over the flame until the loop emits a colourless flame.
- Step 4: To the salt sample taken in a watch glass, add 2-3 drops of concentrated hydrochloric acid (HCl) using a dropper.
- Step 5: Make a paste by mixing the salt and concentrated hydrochloric acid (HCl).
- Step 6: Dip the cleaned platinum wire into the sample paste and hold it to the flame.
- Step 7: Observe the colour of the flame.
- Step 8: Hold the blue glass (cobalt glass) in front of the flame and observe the colour of the flame.
- Step 9: Refer to the inference table and report the possible cation present.
- Step 10: Repeat the experiment for each of the given samples.
In this experiment, we performed the flame test to detect certain cations by making a sample paste using concentrated hydrochloric acid (HCl) and holding it to a non-luminous flame using a platinum wire.
| Sl. No. | Cation | Flame colour (naked eye) | Flame colour (blue glass) |
|---|---|---|---|
| 1 | Sodium | Golden yellow | Not visible |
| 2 | Potassium | Lilac | Pink/Lilac |
| 3 | Calcium | Brick red | Green |
| 4 | Barium | Apple green | Bluish-green |
| 5 | Lithium | Carmine red | Violet |
| 6 | Copper | Bluish green | Bright green |
| 7 | Strontium | Crimson | Purple |
| 8 | Lead | Pale blue | Blue |
FAQs on Flame Test
Q: Why do metal salts give colour when kept in a flame?
Ans: The flame’s energy is high enough for the electrons to get excited to higher energy levels. When the electrons return to the ground state, they release photons of the same energy.
Q: Why does a glass rod not hold the salt paste to the flame?
Ans: Glass rods are usually made of sodium silicates, and the sodium in them imparts its colour to the flame.
Q: Why is the platinum wire used in the flame test?
Ans: Platinum is perfect for this because it is unreactive and does not produce a colour in the flame that will mask other metals’ presence.
Q: What is used for cleaning the loop of platinum wire?
Ans: Platinum wire must be cleaned with distilled water and washed with hydrochloric acid to remove traces of any impurities or analytes. The compound is usually made into a paste with concentrated hydrochloric acid, as metal halides, being volatile and giving better results in the flame test.
Q: What is the colour of copper salt given off in the flame test?
Ans: Blue.
JEE Main