Neco 2019 Chemistry Question 8

Practice essay / theory question 8 from the 2019 Neco Chemistry examination. This question covers solubility, quantitative analysis, experimental design .

Neco 2019 Chemistry Essay / Theory

Topics: solubility quantitative analysis experimental design

Question 8 NECO • 2019 • CHEMISTRY • essay

A student is investigating the solubility of potassium nitrate (KNO3) in water using the apparatus shown. The set‑up consists of a 250 mL beaker placed in a thermostatically controlled water bath, a thermometer, a magnetic stirrer, a digital balance, a funnel fitted with filter paper, and a graduated cylinder for measuring water volume. The student adds a known excess of solid KNO3 to 100.0 mL of distilled water, heats the mixture to a desired temperature, stirs until saturation, then quickly filters the hot solution to separate undissolved solid. The mass of the solid recovered on the filter paper is measured.

Question Parts

( a )

State the purpose of each component of the apparatus and explain the principle behind this method of determining solubility.

( b )

The experiment was carried out at two temperatures. (i) At 30 °C, 20.0 g of KNO3 was added to 100.0 mL of water and the solution was saturated. After filtration, 3.2 g of solid KNO3 was recovered. Calculate the solubility (g per 100 mL water) at 30 °C. (ii) At 60 °C, 40.0 g of KNO3 was added to 100.0 mL of water and the solution was saturated. After filtration, 5.6 g of solid KNO3 was recovered. Calculate the solubility (g per 100 mL water) at 60 °C.

( c )

Assuming that solubility varies linearly with temperature between 30 °C and 60 °C, estimate the mass of KNO3 required to prepare 250.0 mL of a saturated solution at 45 °C.

( d )

Identify two factors, other than temperature, that could affect the measured solubility in this experiment and suggest a modification to the experimental design to minimise each factor.

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About This Question

This is Neco 2019 Chemistry Question 8. It is one of the essay questions from the 2019 Neco Chemistry examination.

The question covers solubility, quantitative analysis, experimental design .

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