Neco 2017 Chemistry Question 8

Practice essay / theory question 8 from the 2017 Neco Chemistry examination. This question covers solubility, laboratory techniques .

Neco 2017 Chemistry Essay / Theory
Topics: solubility laboratory techniques
Question 8 NECO • 2017 • CHEMISTRY • essay
Neco 2017 Chemistry Question 8 diagram

A student investigates the solubility of potassium nitrate (KNO\(_3\)) in water using the apparatus shown. The student records the mass of KNO\(_3\) that dissolves in 100 mL of distilled water at the temperatures indicated below: | Temperature (°C) | Mass of KNO\(_3\) dissolved (g) | |------------------|---------------------------------| | 20 | 13.3 | | 40 | 20.9 | | 60 | 31.6 | | 80 | 45.8 | The thermometer used has an uncertainty of \(\pm0.5\)°C. The apparatus consists of a 250 mL beaker, a water bath with temperature control, a thermometer, a stirring rod, a balance and filter paper as illustrated. Answer the following questions:

Question Parts

( a )
Describe qualitatively the solubility curve that would be obtained from the data and explain the relationship between temperature and the solubility of KNO\(_3\).
( b )
Estimate, by linear interpolation, the mass of KNO\(_3\) that will dissolve in 100 mL of water at 70°C. Show all steps.
( c )
The student wishes to prepare a saturated solution of KNO\(_3\) at 70°C in 250 mL of water. Using your result from part (b), calculate the mass of KNO\(_3\) required. Then, if the solution is allowed to cool to 20°C without any crystallisation control, determine how much KNO\(_3\) will precipitate out. State any assumptions made.
( d )
Identify two possible sources of experimental error in this determination of solubility and explain how each could affect the reported solubility values.

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About This Question

This is Neco 2017 Chemistry Question 8. It is one of the essay questions from the 2017 Neco Chemistry examination.

The question covers solubility, laboratory techniques .

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