Waec Model Questions Vol1 2020 Chemistry Question 2

Practice practical question 2 from the 2020 Waec Model Questions Vol1 Chemistry examination. This question covers Flame test, Periodic trends, Solubility in acids, Emission of light, Energy‑wavelength relationship .

Waec Model Questions Vol1 2020 Chemistry Practical
Topics: Flame test Periodic trends Solubility in acids Emission of light Energy‑wavelength relationship
Question 2 WAEC_MODEL_QUESTIONS_VOL1 • 2020 • CHEMISTRY • practical

A student carries out a flame‑test investigation to identify the metal ion present in an unknown aqueous sample (Sample U). The student prepares four standard solutions containing 0.10 M of Na⁺, K⁺, Ca²⁺ and Ba²⁺ respectively. A small amount of each solution is placed on a clean nichrome wire loop and introduced into a non‑luminous Bunsen‑burner flame. The observed flame colours are recorded. The same procedure is then performed with Sample U. In addition, the student adds a few drops of dilute HCl to a separate portion of Sample U and notes whether a precipitate forms.

Question Parts

( a )
State the flame colour observed for each of the four standard metal ions.
( b )
The flame of Sample U appears lilac and a white precipitate forms on addition of dilute HCl. Identify the metal ion(s) present in Sample U and give a brief justification using the observations and periodic‑table trends.
( c )
The lilac flame of potassium is due to an electronic transition that releases energy of 2.5 eV. Calculate the wavelength of the emitted radiation in nanometres (nm). (Use h = 6.626 × 10⁻³⁴ J·s, c = 3.00 × 10⁸ m s⁻¹, 1 eV = 1.602 × 10⁻¹⁹ J.)

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About This Question

This is Waec Model Questions Vol1 2020 Chemistry Question 2. It is one of the practical questions from the 2020 Waec Model Questions Vol1 Chemistry examination.

The question covers Flame test, Periodic trends, Solubility in acids, Emission of light, Energy‑wavelength relationship .

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