ijmb model questions vol1 2017 chemistry | Practical

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Question 1 View Details
A hydrogen discharge tube is connected to a simple spectroscope whose scale reads 0.1° per 5 nm of wavelength. The following angles were recorded for three visible lines of the hydrogen spectrum: - Line 1: 13.12° - Line 2: 10.50° - Line 3: 9.00° Using the Balmer formula 1/λ = R (1/2² – 1/n²) where n = 3, 4 and 5 respectively, determine the Rydberg constant (R) from the experimental data.
Question Parts
(a)
Convert each measured angle into the corresponding wavelength in nanometres.
(b)
For each wavelength calculate the value of the Rydberg constant using the Balmer relation. (Take n = 3 for line 1, n = 4 for line 2 and n = 5 for line 3.)
(c)
Calculate the average value of R from the three determinations.
(d)
Comment on the accuracy of the experimental Rydberg constant by comparing it with the accepted value 1.097×10⁷ m⁻¹.
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Question 2 View Details
A 0.250 g sample of an unknown metallic solid was placed in a conical flask containing excess dilute hydrochloric acid. The hydrogen gas produced was collected over water at 25 °C. The volume of gas collected was 112 mL. Atmospheric pressure was 760 mm Hg and the vapour pressure of water at 25 °C is 23.8 mm Hg. Assume the metal reacts according to M + 2HCl → MCl₂ + H₂ (1 mol metal : 1 mol H₂). Using the data, determine the atomic mass of the metal and identify the element from the periodic table.
Question Parts
(a)
Calculate the pressure exerted by the dry hydrogen gas.
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Question 3 View Details
A laboratory investigation was carried out to classify three solid compounds (X, Y and Z) based on the nature of the chemical bond present. The observations recorded are shown in the table below. | Compound | Conductivity of aqueous solution | Solubility in water | Melting point (°C) | Appearance | |----------|-----------------------------------|---------------------|-------------------|------------| | X | High (conducts electricity) | Very soluble | 820 | White crystalline solid | | Y | Negligible (does not conduct) | Slightly soluble | 150 | Colourless powder | | Z | Moderate (conducts when molten) | Insoluble | 1350 | Grey metallic lump | Using the data, answer the following questions:
Question Parts
(a)
State the type of bonding (ionic, covalent or metallic) exhibited by each compound X, Y and Z.
(b)
Explain why the melting point of compound Y (covalent) is considerably lower than that of compound X (ionic) even though both are solids at room temperature.
(c)
Suggest one additional practical test that could be performed to confirm the nature of bonding in compound Z and justify why it is appropriate.
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Question 4 View Details
A 0.500 g sample of an impure sodium carbonate (Na₂CO₃) was dissolved in distilled water and the resulting solution was titrated with 0.100 M hydrochloric acid (HCl) using phenolphthalein as indicator. The titration required 23.45 mL of the acid to reach the endpoint.
Question Parts
(a)
Calculate the number of moles of HCl used in the titration.
(b)
Write the balanced chemical equation for the reaction between Na₂CO₃ and HCl and state the stoichiometric ratio between Na₂CO₃ and HCl.
(c)
Using the data above, calculate (i) the mass of pure Na₂CO₃ present in the sample and (ii) the percent purity of the sample.
(d)
Identify one source of error related to the titration procedure and one related to the sample preparation. Explain how each error would affect the calculated percent purity.
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