Matter can be defined as any substance that has inertia, occupies space and has mass. How is matter classified? Scientists of the world classify matter as solid, liquid or gas, but there is one more interesting way to classify it. Matter can also be classified as pure substances and mixtures.
The colloid particles are attracted toward water. They are also called reversible sols. These are opposite in nature to hydrophilic colloids. The colloid particles are repelled by water. They are also called irreversible sols. In some cases, a colloid suspension can be considered a homogeneous mixture.
This is because the distinction between "dissolved" and "particulate" matter can be Pure substances and mixtures a matter of approach, which affects whether or not it is homogeneous or heterogeneous.
Interaction between particles The following forces play an important role in the interaction of colloid particles: This refers to the impossibility of any overlap between hard particles.
Colloidal particles often carry an electrical charge and therefore attract or repel each other. The charge of both the continuous and the dispersed phase, as well as the mobility of the phases are factors affecting this interaction.
This is due to interaction between two dipoles that are either permanent or induced. Even if the particles do not have a permanent dipole, fluctuations of the electron density gives rise to a temporary dipole in a particle.
This temporary dipole induces a dipole in particles nearby. The temporary dipole and the induced dipoles are then attracted to each other. This is known as van der Waals force, and is always present unless the refractive indexes of the dispersed and continuous phases are matchedis short-range, and is attractive.
According to the second law of thermodynamics, a system progresses to a state in which entropy is maximized. This can result in effective forces even between hard spheres[ how?
Steric forces between polymer-covered surfaces or in solutions containing non-adsorbing polymer can modulate interparticle forces, producing an additional steric repulsive force which is predominantly entropic in origin or an attractive depletion force between them.
Such an effect is specifically searched for with tailor-made superplasticizers developed to increase the workability of concrete and to reduce its water content.
Preparation There are two principal ways of preparation of colloids: Condensation of small dissolved molecules into larger colloidal particles by precipitation, condensation, or redox reactions.
Such processes are used in the preparation of colloidal silica or gold. Stabilization peptization The stability of a colloidal system is defined by particles remaining suspended in solution at equilibrium.
Stability is hindered by aggregation and sedimentation phenomena, which are driven by the colloid's tendency to reduce surface energy. Reducing the interfacial tension will stabilize the colloidal system by reducing this driving force.
Examples of a stable and of an unstable colloidal dispersion. Aggregation is due to the sum of the interaction forces between particles. Electrostatic stabilization and steric stabilization are the two main mechanisms for stabilization against aggregation.
Electrostatic stabilization is based on the mutual repulsion of like electrical charges. In general, different phases have different charge affinities, so that an electrical double layer forms at any interface.
Small particle sizes lead to enormous surface areas, and this effect is greatly amplified in colloids. In a stable colloid, mass of a dispersed phase is so low that its buoyancy or kinetic energy is too weak to overcome the electrostatic repulsion between charged layers of the dispersing phase.
Steric stabilization consists in covering the particles in polymers which prevents the particle to get close in the range of attractive forces.
A combination of the two mechanisms is also possible electrosteric stabilization. All the above-mentioned mechanisms for minimizing particle aggregation rely on the enhancement of the repulsive interaction forces. Particle sedimentation and also floating, although this phenomenon is less common arises from a difference in the density of the dispersed and of the continuous phase.
The higher the difference in densities, the faster the particle settling. The gel network stabilization represents the principal way to produce colloids stable to both aggregation and sedimentation. Examples of such substances are xanthan and guar gum. Steric and gel network stabilization.In chemistry, a colloid is a mixture in which one substance of microscopically dispersed insoluble particles is suspended throughout another substance.
Sometimes the dispersed substance alone is called the colloid; the term colloidal suspension refers unambiguously to the overall mixture (although a narrower sense of the word suspension is distinguished from colloids by larger particle size).
The individual substances in a mixture can be separated using different methods, depending on the type of mixture. These methods include filtration, evaporation, distillation and chromatography. The CLP Regulation (for "Classification, Labelling and Packaging") is a European Union regulation from , which aligns the European Union system of classification, labelling and packaging of chemical substances and mixtures to the Globally Harmonised System (GHS).
It is expected to facilitate global trade and the harmonised communication of hazard information of chemicals and to promote.
Aug 30, · Pure substances cannot be separated into any other kinds of matter, while a mixture is a combination of two or more pure substances. 2. A pure substance has constant physical and chemical properties, while mixtures have varying physical and chemical properties (i.e., boiling point and melting point).
Melting Point and Freezing Point. Pure, crystalline solids have a characteristic melting point, the temperature at which the solid melts to become a srmvision.com transition between the solid and the liquid is so sharp for small samples of a pure substance that melting points can be measured to o C.
The melting point of solid oxygen, for example, is o C.
Available online at srmvision.com International Journal of Pharmaceutical Sciences and Drug Research ; 4(1): 63 Research Article ISSN X Development and Validation of Related Substances Method by HPLC.