Question

State three advantages of alcohol over mercury for using it as a thermometric liquid.

Answer 1

Hint: Liquid used in thermometer must be sensitive to slight change in temperature. Liquid used in a thermometer depends on the change in volume of the liquid with temperature. Liquid must have a high coefficient of expansion.

Complete step by step answer:
The science of temperature and its measurement is called thermometry. An instrument designed to measure the temperature is called a thermometer. There are many kinds of thermometers. The property of a substance which changes sufficiently with temperature can be used as the basis of constructing thermometers.

In general, a thermometer uses some measurable property of a substance which is sensitive to temperature change. Liquid in thermometers are suitable for narrow change of measurements.
The most commonly used liquid is mercury. The range of mercury thermometer is
$39^\circ \;{\rm{C}}$ to $357^\circ {\rm{C}}$.

The three advantages of mercury are:
1. It expands uniformly when heated.
2. It has a high boiling point (357 °C) and a low freezing point (-39 °C).
3. It does not stick to the walls of the glass tube.

Additional Information: Mercury does not wet the solid. The resultant adhesive force between liquid and solid on a mercury molecule is smaller than resultant cohesive force. Therefore, their resultant force lies inside the liquid.

Note: When mercury is in contact with a solid, the angle between tangent drawn to the free surface of the liquid of mercury and the surface of solid at the point of contact measured inside the mercury is obtuse. Alcohol thermometers are also used to measure temperatures but near ice point only.