Question

Hydrometer is used to determine which of the following?
A. Specific gravity of liquids.
B. Boiling point of water.
C. Specific heat of a matter.
D. Specific humidity

Answer 1

Hint: Recall the methods of measuring the density of an unknown liquid. We can also test the purity of various liquids with the help of hydrometer by noting down the level, up to which stem of hydrometer sinks inside the liquid.

Complete step by step answer:
A hydrometer measures the density of liquids. It is made of clear glass and is most often approximately 8 inches long (standard size).

Hydrometers are primarily used to determine the density of an unknown liquid or specific gravity.

\[\text{Density}\left( \rho \right)\text{ = }\dfrac{\text{mass of the liquid }\left( \text{m} \right)}{\text{volume of the liquid }\left( \text{V} \right)}\]

\[\text{Specific gravity = }\dfrac{\text{mass of the unknown liquid }\left( {{\text{m}}_{1}} \right)}{\text{mass of an equal volume of distilled water }\left( \text{at }{{\text{4}}^{\circ }}\text{C} \right)\text{ of a known liquid }\left( {{\text{m}}_{2}} \right)}\]

The hydrometer operates on Archimedes Principle.

Archimedes discovered that when a body, which is lighter than a fluid is placed in that fluid, the fluid displaced by the body will be equal to the volume of the body. This principle is also known as buoyancy.

Hydrometers consist of two parts:
a.) A stem
b.) A bulb

Hence, the correct option is A, i.e., Specific gravity of liquids.

Additional Information:
To ensure an accurate measurement, keep the hydrometer free-floating in the centre of the liquid’s container. This will keep the hydrometer closest to the centre of the liquid’s meniscus. After taking the measurement, carefully remove the hydrometer from the liquid by the stem. Be sure to rinse the hydrometer with distilled water after each measurement taken and before storage.

Note: Students should understand the principle and working method of hydrometer, thereafter they need to know how to calculate the specific gravity of an unknown substance by noting down the readings from the hydrometer. In this way students can answer this type of apparatus related questions easily.