Neco 2023 Chemistry Question 4

Practice practical question 4 from the 2023 Neco Chemistry examination. This question covers Mole Concept .

Neco 2023 Chemistry Practical

Topic: Mole Concept

Question 4 NECO • 2023 • CHEMISTRY • practical

A volatile liquid of unknown composition is to be analysed for its molar mass by the vapour‑density method. Procedure: 1. Accurately weigh 0.500 g of the liquid and place it in a 250 mL flask. 2. Heat the flask until the liquid vaporises and the vapour completely fills the flask. 3. The vapour is then collected over water at 25.0 °C. The volume of vapour collected is 180.0 mL. 4. Atmospheric pressure at the time of the experiment is 760 mmHg and the vapour pressure of water at 25.0 °C is 23.8 mmHg. Using the data above, answer the following questions.

( a )

Calculate the partial pressure of the vapour of the unknown liquid (in atm).

( b )

Determine the number of moles of vapour collected using the ideal‑gas equation (R = 0.0821 L·atm·mol⁻¹·K⁻¹).

( c )

Calculate the molar mass (g·mol⁻¹) of the unknown liquid.

( d )

Identify two possible sources of systematic error in this experiment and explain how each would affect the calculated molar mass.

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This is Neco 2023 Chemistry Question 4. It is one of the practical questions from the 2023 Neco Chemistry examination.

The question covers Mole Concept .

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