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How to Separate a Mixture of a Solid and a Liquid?

  • Difficulty Level : Medium
  • Last Updated : 16 Sep, 2021

In our daily life, we use different products. And, always keep in search of pure products as mostly also found written on the packaging of items. But scientifically the term pure is used for those matters which are made up of particles that have the same chemical nature or formation. Hence, the majority of substances surrounding us are mixtures of two or more constituent particles. Anything that has mass and occupies space made up of small tiny particles is called matter. As the mixture consists of different constituents, these constituents can be separated with the help of some physical methods like handpicking, weaving, sedimentation, etc.

In the article, we focused on the methods of separation used to separate the constituents from a mixture of a solid and liquid. The methods include the process of sedimentation, filtration, crystallization, and evaporation in which solid can be obtained separately in a dry state as well as liquid in its pure form.

Mixture

The combination of two or more different kinds of particles is called a mixture. These particles do not show any kind of chemical reaction with each other but are physically bonded.

The result of the combination of components does not lose their uniqueness, nor are they chemically merged. A mixture is the final result of mechanically blending or combining chemical components such as elements and compounds. Mixtures are made up of two or more unrelated compounds that have not been chemically mixed. The following are the properties of mixtures.

  • Each component of a combination retains its original characteristics.
  • The separation of components is simple.
  • The percentage of each component varies.

Types of Mixture

  • Homogeneous mixture: A heterogeneous combination is sand combined with salt, for example. Heterogeneous mixtures have varied characteristics and compositions in different sections of the mixture, implying that the attributes are not uniform across the combination. e.g. air, oil, and water, etc.
  • Heterogeneous mixture: Homogeneous mixtures are those that have the same characteristics and combinations across their mass. e.g. sand, common salt, etc.

Separation of Mixture of Solid and Liquid

A mixture of solid and liquid can be found in a homogeneous solution or heterogeneous mixture. The liquid in which the solid substance is mixed or gets dissolved is known as a solvent. Whereas, the dissolving solid constituent is known as solute. These solute and solvents can be separated in their pure form by the usage of different techniques for the separation of mixtures.

Some common methods to separate solid and liquid from a mixture are mentioned below:

  • Evaporation,
  • Filtration,
  • Sedimentation, and
  • Crystallization.

Evaporation

Evaporation is the method of separating a solid (solute) from a homogeneous solution. in this method, the solution is heated until the solvent gets evaporated in the form of vapor and the solute is left behind as residue. The process involves the technique of vaporization.

The liquid substance which dissolves the solid substance or solute is called a solvent. Whereas, the solid substance which gets dissolved in a liquid is called the solute. Let’s understand the process with a demonstration of the given figure

The process of evaporation 

  • Prepare a small amount of homogeneous solution in a beaker.
  • Now, heat the beaker until you see the water getting evaporated.
  • Then, continue heating as the evaporation goes on and stop heating when you see a dry powder-like substance left behind in the beaker.

Here, the water is separated in the form of vapor and solid is obtained in the dry state.

Factors Affecting Rate of Evaporation 

  1. Temperature: As the temperature increases the kinetic energy of the particles also increases accordingly which increases the rate of evaporation. For example, water at room temperature boils faster than cool water as its temperature is higher.
  2. Pressure: Pressure and rate of evaporation are indirectly proportional to each other. As the pressure increases the rate of evaporation decreases accordingly.

Advantages of Evaporation

  • This process is used to extract drinkable water from seawater.
  • It can also be generally used as a concentrating process.
  • The process is used to extract metals and minerals from water.

Disadvantages of Evaporation

  • The process requires lots of heat energy.
  • The process is not suitable for the separation of insoluble solute.
  • The vapor needs to go under condensation to be preserved or collected in a liquid state.

Application of Evaporation

  1. The process of evaporation is generally applicable to separate solids (sugar and salt)from their respective solutions.
  2. Separation of Sugar Solution: Firstly, take a bowl of water and mix some amount of sugar in it to form a solution. Then, heat the given solution until the water gets vaporized and sugar is obtained in solid-state, left behind as residue. In this process, water acts as a solvent and sugar as a solute. However, the sugar obtained as the residue is not in its pure crystallized state. It will rather be gained in decomposed form.
  3. Separation of Salt Solution: Just take a spoon of salt and mix it with water to form a salt solution. Now, heat the solution gradually until the water gets evaporated in form of vapor and salt is left behind as residue.  In this process, salt is solute and water is solvent. The residue of salt left in the container is decomposed or not in crystal form.

Filtration

Filtration is the process of separating small solid particles with the help of a filtering agent (i.e. filter paper, cloth, or other). The process is carried out with the help of permeable parchment paper in which the water penetrates through the paper while the solid particles which cannot pass through get collected on it.

The Process of Filtration

For example, we can filter insoluble solid particles from a mixture of sand and water with the help of filter paper. The clear water received in the beaker is called filtrate and the solid particles which remain are called the residue. 

Factors affecting Filtration

  1. Permeability: The permeability rate of the parchment paper or filtering agent decides the purity of the liquid. As if the permeability is high then the impurities will also skip into the filtrate.
  2. Solubility of solute: The process can be only applicable for insoluble solute substances which do not dissolve completely. The filtration process is not preferred for the separation of components homogeneous mixture.

Advantages of filtration

  • It does not require heat energy for processing.
  • Filtration is an affordable method of purification.
  • The filtrate obtained after the process is clear in the majority of cases.

Disadvantages of Filtration

  • The process does not filters inorganic or organic matters which are comparatively tiny in size.
  • The process is not applicable for homogeneous solutions.
  • Normally, the technique of filtration is not preferred for the separation of other matters like colloid, etc

Application of Filtration

  1. Filtration plays a very essential role in water treatment. Many countries use it to extract drinking water from seawater or used wastewater.
  2. It is the process normally used in homes for straining brewed tea or coffee, etc
  3. Air conditioners, vacuum cleaners, water purifiers, and many other appliances come with attached filters in them.

Sedimentation 

It is the process in which heavy solid particles of the mixture get settled down at the bottom of the container while clear water gets separated.

It is defined as the process through which solids are separated from liquids. All of the solids sink to the bottom of the beaker, leaving a clear layer of liquid on top. Sedimentation is the process through which heavier contaminants in a liquid, often water, settle to the bottom of the container housing the mixture. It takes some time to complete the process. 

A simple experiment may be used to study the sedimentation process. Fill a jar halfway with garden type mud, add some water, shake vigorously, and leave it alone for a few minutes. After a period, the gravel and rocks have settled below, stand above, and so on. Essentially, the garden variety mud has produced soil layers based on various.

Crystallization

Crystallization is the process of separating a solid from a liquid solution. This process is carried out by cooling highly concentrated solutions. 

Crystallization is generally used to obtain the pure form or crystal of any substance. In the process, crystals are extracted from a supersaturated solution, and the liquid left behind is termed as mother liquor. Crystallization is the process by which the atoms or molecules of a substance organise themselves in a well-defined three-dimensional lattice, reducing the total energy of the system. When a material is crystallised, its atoms or molecules link together at well-defined angles.

The Process of Crystallization 

Factors affecting Crystallization

  1. Temperature: temperature affects the rate of crystallization as the required amount of heat provided to the system needs to be checked. If the temperature exceeds the process will turn out into evaporation and the crystal formed will get decomposed.
  2. Concentration of the solution: As crystallization takes place by cooling of supersaturated solution. As the temperature increases the solubility of the substance increases and as concentrated the solution gets pure and a pretty form of a crystal can be obtained.

Advantages of crystallization

  • This process can give out the purified form of a solid state.
  • It is an affordable method of purification or separation.
  • It requires a low amount of heat or energy to be carried out.

Disadvantages of Crystallization

  • This process cannot be preferred as a high value-added process for product formation.
  • The process is only applicable for the purification of a single component.

Sample Problems

Problem 1: Can a heterogeneous mixture be the solution?

Solution:

A solution consists of soluble solute uniformly distributed in it and cannot be seen through naked eyes. Whereas, in a heterogeneous mixture, there is no uniform composition.

Problem 2: What would you consider seawater a homogeneous or heterogeneous mixture?

Solution:

As we know that seawater consists of salt that can only be removed by the process of evaporation whereas, seawater also contains sand and dead or decaying bodies which makes it a heterogeneous mixture.

Problem 3: Which is more preferential evaporation of crystallization?

Solution:

The crystallization process is preferred over evaporation because of the following reasons:

  • The crystallization process provides a pure form of substance.
  • Evaporation gives impure substance which is furthered purified by crystallization, and
  • Evaporation is not preferred for salt or sugar formation can decompose or burn.

Problem 4: Differentiate between homogeneous and heterogeneous mixture.

Homogeneous mixtureHeterogeneous mixture

1. In this mixture the components are equally 

our r uniformly distributed.

1. In this mixture the components are not uniformly distributed.

2. Dissolved solid cannot be seen through naked

eyes.

2. Solid can be seen through naked eyes. 

Problem 5. How would you know that the given liquid is pure water? 

Ans. We can find out by the process of evaporation as allow the liquid to evaporate and if there’s no residue left behind then, the liquid is pure.

Problem 6. Are all the materials present around us pure?

Ans. No, a pure substance is a substance that contains the same kind of particles. And, most of the things found around us consists of two or more kind of components.

Problem 7. Is the solution always found in a liquid state?

Solution:

No, the solution is found in solid, liquid as well as gaseous states. As air is an example of gaseous solution and alloy is a solution found in a solid-state.


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