Waec Model Questions Vol1 2018 Chemistry Question 8

Practice essay / theory question 8 from the 2018 Waec Model Questions Vol1 Chemistry examination. This question covers solubility, thermodynamics, experimental_methods .

Waec Model Questions Vol1 2018 Chemistry Essay / Theory
Topics: solubility thermodynamics experimental_methods
Question 8 WAEC_MODEL_QUESTIONS_VOL1 • 2018 • CHEMISTRY • essay

A student is investigating the solubility of potassium nitrate (KNO₃) in water using the apparatus shown in the diagram. The set‑up consists of a beaker placed on a water‑bath, a calibrated thermometer, a magnetic stirrer, and a filter funnel with a pre‑weighed dry filter paper. The student records the mass of KNO₃ that dissolves in 100 mL of water at three different temperatures as follows: • 30 °C → 32.0 g per 100 mL • 50 °C → 55.0 g per 100 mL • 70 °C → 84.0 g per 100 mL Using this data, answer the following questions:

Question Parts

( a )
Assuming a linear relationship between solubility (g · 100 mL⁻¹) and temperature (°C), estimate the solubility of KNO₃ at 90 °C.
( b )
Using the van’t Hoff equation \(\ln S = -\dfrac{\Delta H_{sol}}{R}\dfrac{1}{T}+\text{constant}\), where \(S\) is the molar solubility (mol L⁻¹) and \(R = 8.314\,\text{J mol}^{-1}\text{K}^{-1}\), calculate the approximate enthalpy change \(\Delta H_{sol}\) (in kJ mol⁻¹) for the dissolution of KNO₃. Use the data at 30 °C and 70 °C only. Show all steps.
( c )
Explain, in terms of the sign of \(\Delta H_{sol}\), why the solubility of KNO₃ increases with temperature.
( d )
Suggest two practical improvements that could be made to the experimental procedure to increase the reliability of the solubility determination.

Detailed Solution & Marking Scheme

Get the step-by-step solution, key points required by examiners and detailed marking guidance through the Edcrib AI Tutor.

Reveal Answer

About This Question

This is Waec Model Questions Vol1 2018 Chemistry Question 8. It is one of the essay questions from the 2018 Waec Model Questions Vol1 Chemistry examination.

The question covers solubility, thermodynamics, experimental_methods .

View More Waec Model Questions Vol1 2018 Chemistry Questions More Waec Model Questions Vol1 Practice Questions Back to Questions

Master the Exam!

You've seen a preview, but there are thousands more questions plus AI tutor to break down complex solutions.

Unlock Full Access Available for Android & Windows
Chat with Support