Determination of Specific Gravity

OBJECTIVE

To determine specific gravity of a liquid using Hydrometer Method. 

APPARATUS

Hydrometer, glass cylinders. 

THEORY

Specific gravity or relative density is the ratio of the density of the fluid to the density of water at standard temperature in example at 40C. Specific gravity can be determined directly from the density of a liquid as measured divided by standard density of water. A convenient alternative method is to use a specially calibrated instrument called Hydrometer. Hydrometer is hallows glass float designed to float upright in liquids of various densities. The depth to which it sinks in the liquid is a measure of the density of the liquid. A scale is provided on its stem which is calibrated to read specific gravity. The sensitivity of the hydrometer depends on the diameter of the stem. A very sensitive hydrometer has a large bulb and thin stem. 

PROCEDURES

1. The tall glass cylinders are placed on the flat working surface.
2. A liquid is filled to allow air to rise to the top.
3. The hydrometer is inserted carefully to allow it to settle in the center of the cylinder.
4. The scale is read after the hydrometer has settled at the bottom of the free water surface.
5. The reading is recorded. The hydrometer is taken out.
6. The procedure 3 to 5 is repeated three times for the other given liquids also.
7. The specific gravities are compared.

DISCUSSION

The specific gravity of mercury is the same on the moon. It is because specific gravity is the ratio of the density of the fluid to the density of water at 40C while density is mass per unit of volume. The mass and volume does not change even on the moon or on the earth. But, the weight will change on the moon. Thus, the specific gravity of mercury does not change on the moon. 

The hydrometer sinks more in the lighter liquids than the heavier because the lighter liquids are less dense than the heavier liquids. In this experiment, water is the lowest with its average specific gravity is 0.95 while the average specific gravity of syrup and oil are 1.25 and 0.88 respectively. From the result, we know that the density of syrup is the highest and the density of water is the lowest. Therefore, the less dense of the liquids, the lowest specific gravity will achieve. 

It is so easy to swim in the sea water than swimming pools because the density of sea water is higher than water in the swimming pools. The higher density of sea water is influenced by the existence of the salt. Thus, it is easily to swim in the sea than in swimming pools. 

CONCLUSION

The specific gravity of a liquid was successful achieved by using Hydrometer Method. Thus, the objective can be accepted.

REFERENCES

1. Andreas Alexandrou, (2001). Principle Of Fluid Mechanics, New Jersey.
2. Suhaimi Abu Talib, (2002). Fluid Mechanics, Penerbit Anda.
3. http://www.icllabs.com/Safety%20Blue%20API%20hydro.JPG