WAEC Chemistry 2023 Theory — Question 10

Model answer

A small quantity of benzoic acid crystals is placed into a capillary tube sealed at one end. The filled capillary tube is tied to a thermometer such that the bulb of the thermometer is completely immersed. The set-up is clamped and lowered into a beaker half-filled with liquid paraffin, placed on a tripod stand with wire gauze. The beaker's contents are heated gently with constant stirring of the liquid paraffin, and the temperature is noted at which the benzoic acid begins to melt (t1) and the temperature at which it is completely liquefied (t2). The melting point is reported as the range (t1 – t2) °C. The process is repeated using a fresh sample of benzoic acid until the readings agree within 2.0°C.