Waec Model Questions Vol1 2024 Chemistry Question 1

Practice practical question 1 from the 2024 Waec Model Questions Vol1 Chemistry examination. This question covers Atomic Structure, Emission spectra, Energy of electronic transitions .

Waec Model Questions Vol1 2024 Chemistry Practical

Topics: Atomic Structure Emission spectra Energy of electronic transitions

Question 1 WAEC_MODEL_QUESTIONS_VOL1 • 2024 • CHEMISTRY • practical

A discharge tube containing an unknown gaseous element is connected to a diffraction‑grating spectrometer. The grating has 5 000 lines cm⁻¹ (spacing d = 2.0 × 10⁻⁶ m). The first‑order (n = 1) diffraction angles for four bright lines are recorded as follows: | Line | Diffraction angle (°) | |------|-----------------------| | 1 | 11.8 | | 2 | 12.5 | | 3 | 14.1 | | 4 | 19.2 | Using the data, answer the questions that follow.

Question Parts

( a )

Calculate the wavelength (in nm) of each of the four observed lines. Show one complete calculation and give the remaining answers to the appropriate number of significant figures.

( b )

Identify the unknown element by comparing the calculated wavelengths with the Balmer series of hydrogen. State the element name.

( c )

For the most energetic transition (shortest wavelength), calculate the energy change ΔE in kJ mol⁻¹. Use h = 6.626 × 10⁻³⁴ J s, c = 3.00 × 10⁸ m s⁻¹ and NA = 6.022 × 10²³ mol⁻¹. Show the formula used.

( d )

State two possible sources of error that could affect the wavelength determination.

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About This Question

This is Waec Model Questions Vol1 2024 Chemistry Question 1. It is one of the practical questions from the 2024 Waec Model Questions Vol1 Chemistry examination.

The question covers Atomic Structure, Emission spectra, Energy of electronic transitions .

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