neco model questions vol1 2024 chemistry | Practical

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Question 1 View Details
A student is given an unknown metallic element X. The following experimental procedures are carried out: 1. A small amount of the metal is introduced into a non‑luminous Bunsen‑burner flame and the colour of the flame is observed. 2. Approximately 0.500 g of the metal is placed in a 250 mL conical flask, 50 mL of dilute hydrochloric acid (≈0.10 M) is added and the mixture is allowed to react completely. The gas produced is collected over water in a gas syringe at 25 °C and 760 mmHg. The volume of gas collected is 112 mL. Using the observations and data, answer the questions that follow.
Question Parts
(a)
The flame observed is a bright reddish‑orange colour. Identify the metal X.
(b)
Write the balanced chemical equation for the reaction of X with dilute HCl.
(c)
Using the data provided, calculate the molar mass of X and state whether the result supports the identification made in part (a). (R = 0.0821 L·atm·mol⁻¹·K⁻¹; 1 atm = 760 mmHg; T = 298 K.)
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Question 2 View Details
A student prepares 100 mL of 0.10 M aqueous solutions of three metal nitrates: Mg(NO₃)₂, Al(NO₃)₃ and Ca(NO₃)₂. The solutions are labelled Mg²⁺, Al³⁺ and Ca²⁺ respectively. Conductivity of each solution is measured at 25 °C using a calibrated conductivity meter. The recorded specific conductivities (κ) are: • Mg²⁺ solution: 0.025 mS·cm⁻¹ • Al³⁺ solution: 0.045 mS·cm⁻¹ • Ca²⁺ solution: 0.018 mS·cm⁻¹ Answer the following questions.
Question Parts
(a)
Explain why the conductivities differ even though the three solutions have the same molarity.
(b)
Rank the three metal ions in order of (i) ionic charge and (ii) approximate ionic radius, and predict the order of conductivity based on these trends.
(c)
Calculate the molar conductivity (Λₘ) for each solution and discuss how the calculated values support the periodic trends observed in part (b). (Use Λₘ = κ / c, where κ is in S·cm⁻¹ and c = 0.10 mol·L⁻¹ = 1.0 × 10⁻⁴ mol·cm⁻³.)
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Question 3 View Details
A clean piece of magnesium ribbon is weighed and then reacted with excess dilute hydrochloric acid to form a magnesium chloride solution. The solution is evaporated to dryness and the solid residue is weighed.
Question Parts
(a)
Write the balanced chemical equation for the reaction between magnesium metal and hydrochloric acid.
(b)
The mass of the magnesium ribbon before the reaction was 0.250 g and the mass of the dried solid residue obtained after evaporation was 0.950 g. Using this data, determine the empirical formula of the chloride formed.
(c)
Based on the empirical formula obtained and the observed properties of the solid (white crystalline solid with high melting point and conducts electricity when molten), discuss the type of chemical bond present in the compound.
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Question 4 View Details
An unknown monoprotic acid (HX) is to be analysed to determine its molar mass. A 0.345 g sample of the solid acid is dissolved in distilled water and the solution is transferred to a 250 mL conical flask. The solution is titrated with 0.100 M NaOH using phenolphthalein as indicator. The titration required 30.45 mL of NaOH to reach the endpoint.
Question Parts
(a)
Write the balanced chemical equation for the neutralisation reaction between the acid and NaOH.
(b)
Calculate the number of moles of NaOH used in the titration.
(c)
Using the stoichiometry of the reaction, calculate the number of moles of the acid present in the sample.
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