[Chemistry Class Notes] on Sieving Pdf for Exam

Substances are primarily divided into elements and mixtures. Elements are pure substances and consist of a single type of atoms or molecules. Mixtures consist of two or more elements and they are not pure. Sieving is one of the important techniques that is used for the separation of mixtures into their respective components. This process can be carried out if the components of a mixture differ in terms of their particle size. Sieving is used in multiple areas of human lives in different ways. From cooking to scientific experimentation, sieving acts as an important procedure of separation. 

Sieving is done  using a device for separating materials of different sizes. The material is exposed to  mechanical forces of vertical and horizontal movement with the help of a container with a grid or perforated bottom through which the material is shaken or poured. 

In everyday life, it may be necessary to separate  useful substances from the mixture. This is done in several ways, one of which is  sieving.

The type of separation procedure is chosen after taking into consideration the state of the mixture, that is whether the particles are in solid, liquid or gaseous form and also the size difference in the particles of the components.

Cooking is an important activity where sieving is actively employed. In cooking, a sieve is used to  break the clusters into dry ingredients such as flour, grind them, and combine them for ventilation. Sieves are sieves used to separate solids from liquids. Examples of strainers used for everyday cooking in the kitchen are tea filters used to separate tea leaves from water, and pepper mills and pepper shakers that pass a specific range of pepper particles  and place them on eggs. there is. And toast. The sieve works because large particles cannot pass through the holes in the sieve, but small particles can. Sifting is often used to cook food, but it  has other uses as well. 

Low investment cost, high accuracy and easy handling make sieving analysis a frequently used method for determining  particle size.

It does not require huge time investment or expensive machinery, and these factors contribute to its popularity.

The Sieve

The devices used in the sieving process are called sieves. The most common type of sieve is a kitchen sieve that is used in daily life.  It consists of a net that is stretched on a steel or iron rib. The unwanted material of the larger size gets accumulated on this mesh since the hole size of the sieve is not enough for it to pass through. This results in the effective separation of the two components if they are different physical states.

Scientifically speaking, sieving is an instrument with a perforated or mesh bottom that is used to combine the coarse and fine parts of a coarse material to sift liquids and the like. A practical example of a strainer is a tea strainer used to separate tea leaves from water. The sieve prevents large particles from passing through the holes in the sieve and keeps them in the sieve. 

 Difference Between Sieving and Winnowing

Sieving should not be confused with sieving. It is important to understand that sieving is the separation of solids as determined by size and size, and sieving is the separation of solid liquids as determined by shape and size. Sifting is used to separate the heavy and light components of a mixture by wind or blown air.

While the size and physical state of the components determine the result of sieving, the winnowing weight difference assumes prime significance. The lighter component is blown away by the wind while the heavier one falls down and is collected for later use. This is how winnowing works against sieving. 

Example: –separation of heavier grain particles from lighter husk particles using a winnow.

A Sieve Analysis (or Gradation Test)

Sieving is also employed for higher purposes in scientific research and experimentation. In construction, sieving analysis (or grading test) is a  vibration aid that assesses the particle size distribution (also known as grading) of granular material by passing the material  through a series of smaller and smaller mesh screens and weighing the amount of material. Practice or method. Used by each sieve is retained as part of the total mass. When sieving in civil engineering, a classification test is performed on  aggregate (granule) samples in the laboratory. A  study of characteristic sieves involves nested rows of sieves with  wire mesh  or sieves. Then divide the weight of each sieve sample  by the total weight to get the percentage obtained for each sieve.  There are two types of sieving, dry sieving and wet sieving, which can be done mechanically or manually, depending on the amount and size of particles to be separated. 

Dry sieving is the recommended method for particle size ranges from 40 µm to 125 mm. 

If dry sieving does not allow for an acceptable separation of  individual fractions, wet sieving is recommended for better results.

Sieving – Advantages and Disadvantages of Sieving

Advantages of Sieving

It does not require a lot of skill and is the traditional method used for  separation. It’s a very cheap method because it doesn’t require the installation of advanced equipment. It takes less time than other methods. 

 Disadvantages of sieving 

1. The efficiency of this method depends on  different particle sizes and cannot be used to separate mixtures containing particles of the same size. B. Flour and chalk powder.  2. It is virtually impossible to measure cohesive and cohesive substances such as sprays, emulsions and clays.

Factors in Sieving

There are different types of sieving where different processes and instruments are employed. The nature of the component substances is first analyzed and assessed before a suitable method is adopted for their separation. There are many factors  to consider when choosing the right screening method. Depending on 

Particle type  

The number of particles and the size and density of the particles and materials that need to be separated 

Use different types of sieves with different hole sizes  to separate  coarse and fine aggregate. 

 Applications with Different Screen Types 

Half-height sieve: Used when a small amount of material needs to be sifted. Microplate Sieve: This is used when the particle size of the material is very fine. Wet scrubber Sieve: Clean the material  and stir with enough water to separate the fines. In this case, this is in the range  of 20 µm. Extra Deep Screen: It is used in large quantities of materials and is widely used in the construction industry.

Air Jet Sieves: This is used where the sample is dispersed by air blown out of a rotating nozzle. The measuring range may be extended to ten microns

Grain Sieves: These sieves are used worldwide for testing grains and cereals.