From Atoms to Materials

Experiment skill Stopper the test tube at once so as to prevent the loss of volatile distillate, which may leave a bad smell in the laboratory. Caution •  DO NOT collect fractions of boiling points above 300 °C, because they may contain harmful compounds. •  After collecting all four fractions, let the set-up cool down completely, so that all the remaining vapour condenses. More to discuss Is fractional distillation a physical method or a chemical method? More to do You may design tests for other properties (e.g. viscosity, volatility and flammability) of the fractions. Obtain your teacher’s approval before you do the tests. After a while, a distillate will be collected in the test tube. When no more distillate comes out, remove the test tube and stopper it. Label this fraction A . Its boiling point range is from room temperature to 80 °C. 4 Turn off the gas supply. Observe the four collected fractions. 6 Repeat steps 3–4 with gradually stronger flames, so that fractions of higher boiling point ranges are collected: • Fraction B : 80 °C–150 °C • Fraction C : 150 °C–200 °C • Fraction D : 200 °C–250 °C 5 Results Property Fraction A B C D Boiling point range (°C) Colour (1 – lightest; 4 – darkest) Analysis and conclusion 1. Crude oil can be separated into fractions by fractional distillation. This is based on the differences in the of the hydrocarbons in it. 2. The higher boiling point range of a fraction, the (darker / lighter) its colour. A B C D 13 From Atoms to Materials 85 © United Prime Educational Publishing (HK) Limited 2024 All rights reserved; no part of this publication may be reproduced, photocopied, recorded or otherwise, without the prior written permission of the Publisher. Sample