You can create a saturated solution by:

1. adding solute to liquid until dissolving stops.
2. evaporating a solvent from a solution until the solute begins to crystallize or precipitate.
3. adding seed crystals to a solution that is supersaturated.

If the saturated solution of a substance at a particular temperature is cooled to a lower temperature, then the solubility of the substance decreases and some of the dissolved substance will separate out in form of solid crystals. Hot water will dissolve more substance whereas cold water will dissolve less substance.

You know you have a saturated solution as it will generally contain some undissolved solid solute. At this point adding more solute will not change the concentration of the solution; adding more solute will simply result in more solid at the bottom of the solution. A saturated solution is at equilibrium.

The impure substance will crystallize in a purer form because the impurities won’t crystallize yet, therefore leaving the impurities behind in the solution. A filtration process must be used to separate the more pure crystals at this point.

Common water treatment processes such as flocculation, sedimentation, filtration and disinfection are employed to remove general impurities such as floating and suspended matters, colloidal particles, dissolved organic matter and destruction of disease-causing microorganisms (pathogens).

Impurities can be easily removed if they are either much more soluble or much less soluble in the solvent than the compound of interest. The insoluble material is then filtered while the solution is kept hot (called “hot filtration”), and then the desired compound is crystallized and collected by suction filtration.

Removal of coarse, dispersed and colloidal impurities from water is known as clarification. These impurities may be removed either by filtration or by sedimentation. (b) Filtration: The apparatus used for filtration is called filter and the porous material that fills the filter is known as filtering material or medium.

In theory, insoluble impurities can be removed from a compound fairly easily. The compound is dissolved in a solvent, the solution is filtered to remove the insoluble impurities, and the solvent evaporated to produce the solid compound. The insoluble impurities are left behind in the filter paper.

Word forms: impurities Impurities are substances that are present in small quantities in another substance and make it dirty or of an unacceptable quality. The air in the factory is filtered to remove impurities.

Wash your face regularly. Remove excess dirt and oil from your skin by cleansing it regularly. Washing your face regularly can minimize and prevent impurities of your skin. Use a gentle cleanser. Choose an oil-free cleanser if have very oily skin.

Avoid harsh antibacterial soap and hand sanitizer, and never scrub skin aggressively. “It disrupts the terrain where bacteria thrive,” says Dr. Bowe. Instead, use cleansers and moisturizers with niacinamide or ceramides to bolster your barrier.

Impurities may lower the shelf life of the substances. Impurities may cause difficulties during formulations and use of the substances. Sometimes Impurities changes the physical and chemical properties of the substances. It may change odour, colour, taste of the substance.

Destructive impurities Impurities can be destructive when they obstruct the working nature of the material. Examples include ash and debris in metals and leaf pieces in blank white papers. The removal of impurities is usually done chemically.

Impurities may bring about incompatibility with other substances. Impurities may lower the shelf life of the substances. Impurities may cause difficulties during formulations and use of the substances. Sometimes Impurities change the physical and chemical properties of the substances.

The presence of even a small amount of impurity will lower a compound’s melting point by a few degrees and broaden the melting point temperature range. Because the impurity causes defects in the crystalline lattice, it is easier to overcome the intermolecular interactions between the molecules.

Foreign substances in a crystalline solid disrupt the repeating pattern of forces that holds the solid together. Therefore, a smaller amount of energy is required to melt the part of the solid surrounding the impurity. This explains the melting point depression (lowering) observed from impure solids.

The melting point of a substance depends on pressure and is usually specified at a standard pressure such as 1 atmosphere or 100 kPa. When considered as the temperature of the reverse change from liquid to solid, it is referred to as the freezing point or crystallization point.

So, the melting point depends on the energy it takes to overcome the forces between the molecules, or the intermolecular forces, holding them in the lattice. The stronger the intermolecular forces are, the more energy is required, so the higher the melting point is.

Both dissolving and melting a compound break the inter-molecular bonds between the molecules, replacing them by more flexible interactions in the fluid. If a compound has a very high melting point, this could indicate that the inter-molecular bonds in its solid are very strong; the solid is very well packed.

(i) Charge on the Ions In general, the greater the charge, the greater the electrostatic attraction, the stronger the ionic bond, the higher the melting point.

Covalent crystals have highest melting points because of network structure.

Ionic solids have highest melting point due to strong electrostatic forces of attraction.

Not all solids melt when they are heated. Some may undergo chemical changes as a result of heating. For example paper burns rather than melts.

To put it simply, a diamond cannot melt in lava, because the melting point of a diamond is around 4500 °C (at a pressure of 100 kilobars) and lava can only be as hot as about 1200 °C.

colorless diamonds