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Inorganic and analytical chemistry Types of Mixtures Matter surrounding us is broadly divided into three phasessolids, liquids and gases. : 1) Pure Substance A pure substance can be either an element (just one type of atom) or a compound. elements Mercury compounds water silver NaCl Oxygen sucrose Mixtures Most objects around us are mixtures. – Example: most foods and beverages, air, the chair you are sitting in. • The components are physically mixed together and can be separated by physical methods. • The properties of mixtures depend on the identity and amount of each component in the mixture – Therefore to fully describe a mixture, the composition of the mixture must be stated. • Example: 5% Starch solution, 75:25% Zinc/Copper Alloy • Mixtures can be either uniform in composition (homogeneous) or the composition can vary throughout the sample (heterogeneous). • Homogeneous mixtures = uniform throughout, appears to be one thing – Homogenous mixtures are called solutions. – Solutions can be liquid, gas, or solid – Examples: Sugar dissolved in water (liquid) Air (gas) 14-karat gold (solid mixture of gold, silver, and copper) • Heterogeneous mixtures = non-uniform, contains regions with different properties than other regions – Examples: chocolate chip cookies sand in water Solution is a homogenous mixture of molecules, atoms , or ions of two, or more different substances .Generally one of the components is in large quantity and the others are in small quantities. The large quantity part of the substance is called the solvent in which the smaller quantities called solutes are mixed which is termed as dissolution Solutions in which water is the solvent are called aqueous solutions • Solubility is defined as the amount of solute that dissolves in a given quantity of solvent to form saturated solution. The solubility depends on a number of factors: Kind of solvent, kind of solute, temperature, pressure and physical state of matter. Table 1 General Rule Like dissolves like" *Polar solvent ( water ) is a good solvent for ionic compounds (NaCl). *Gasoline (non polar compounds is a good solvents for other non polar organic compounds (oil). For example, both carbon tetrachloride (CCl4) and benzene (C6H6) are nonpolar liquids. The only intermolecular forces present in these substances are dispersion forces .When these two liquids are mixed, they readily dissolve in each other, because the attraction between CCl4 and C6H6 molecules is comparable in magnitude to the forces between CCl4 molecules and between C6H6 molecules. • Electrolytes Are compounds that dissolve in water to form ions. – The consequences of having too much or too little of a particular electrolyte can have profound effects on your health. The mode of electrolytic and non-electrolytic solutions has been used to explain all the physical properties of solutions(osmosis and dialysis) – Ions important to your health: • Na+, K+ = transmission of nerve impulse • Ca2+ = muscle contraction and blood clotting Arrhenius Theory of Electrolytes When ionic compounds are dissolved in water, the ions released and they distribute themselves uniformly in the water. Polar covalent bonds form ions when dissolved in water, non electrolytes dissolve in water, neutral molecules are released. Hydration: is a close association of water molecules with an ion and the ion said to be hydrate. According to Arrhenius model, the total number of ions formed per mole of electrolyte depends on the chemical formula of the electrolyte. (See table below):- Number of ions formed per mole of electrolyte Chemical formula Ions formed in aqueous solution Number of ions in 1 mole off electrolyte NaCl Na+ Cl- 2*6.02*1023 KNO3 K+ NO-3 2*6.02*1023 CaCl2 Ca+ Cl- Cl- 3*6.02*1023 Na3PO4 Na+ Na+ Na+ PO4-3 4*6.02*1023 Colloids and Suspensions In a true solution, the maximum diameter of a solute particle is about 1 nm. Colloid: A suspension in solvent in which the solute particle diameter is between 1 nm and 1000 nm. Colloid particles have very large surface areas, which causes colloidal systems to have two properties: They scatter light (Tyndall Effect) and, therefore, appear turbid, cloudy, or milky, not transparent. They form stable dispersions; that is, they do not settle out. Colloids are intermediate between homogeneous and heterogeneous mixtures. Properties of Colloids Tyndall effect: a characteristic of colloids in which light passing through the colloid scatters. When we see the beam of a flashlight through smoke, dust or fog we are observing the Tyndall effect. Brownian motion: the random motion of colloid-size particles. An example of Brownian motion is the motion of dust particles in the air; what we see is not the dust particles themselves but the flashes of scattered light passing through the colloid due to the Tyndall effect. Suspensions scatter light. Colloids often scatter light Properties of Colloids Why do colloidal particles remain in solution despite all the collisions due to Brownian motion? In liquids, most colloidal particles are surrounded by a large solvation layer; if the solvent is water, as in the case of protein molecules in the blood, the large number of surrounding water molecules prevents colloidal molecules from touching and sticking together. In gases and liquids, because of their large surface area, colloidal particles acquire static charges; for example, they all may become negatively charged. When a charged colloidal particle encounters another particle of the same charge, they repel each other. Examples of Colloids: Milk • Milk appears to be homogeneous. But under a microscope you see that milk contains globules of fat and small lumps of the protein casein dispersed in a liquid called whey. Milk is colloid because the particles of casein do not settle out after standing. • A suspension contains large particles suspended in a liquid. • The particles will eventually, slowly settle to the bottom in the absence of agitation Suspensions: Muddy Water Summary of Solutions, Colloids ,And Suspensions Diffusion and Osmosis Diffusion and Osmosis Liquid molecules travel randomly in all directions and mix quickly with other liquid molecules in a process called diffusion. Diffusion is the movement of one substance within another substance until it is evenly distributed. Substances move from areas of higher concentration to those of lower concentration by diffusion. Certain membranes, called semipermeable membranes, are barriers to diffusion because they allow solvents, but not all solutes to pass through. • The semipermeable membrane in the image allows water to pass but not the Na+ or Cl- ions Although water moves back and forth through most semipermeable membranes, it flows more forcefully from the side of the membrane with lesser solute concentration to the side with greater solute concentration. The net movement of water across a membrane from a solution of lesser solute concentration to one of greater solute concentration is called osmosis. Osmotic Pressure Semipermeable membrane: A membrane with tiny pores that are big enough to allow solvent molecules to pass through them, but not big enough to allow the passage of large solute molecules. Example: a cell wall! Osmosis: the movement of solvent particles through a semipermeable membrane from a region of lower solute concentration (higher solvent concentration) to a region of higher solute concentration (lower solvent concentration). Osmotic pressure: the pressure necessary to prevent osmosis. Osmolarity (Osmol): the molarity multiplied by the number of particles produced by each formula unit of solute. The pressure associated with the transport of water in the osmosis process is called: osmotic pressure. The greater the difference in solute concentrations across the semipermeable membrane, the greater the osmotic pressure b. As a osmolarity (1 osmole = 1 mole (Avegadros’s # of particles) in 1 kilogram of water) (1) Osmolarity is a reflection of the number of particles in a solution and not the type of particle in a solution. (2) The osmolarity of body fluids is important because it influences the movement of water in and out of cells. *Isotonic solution: a term used primarily in the health sciences to refer to a solution with the same osmolarity as blood plasma and red blood cells. *Hypertonic solution: a solution with higher osmolarity than red blood cells. *Hypotonic solution: a solution with lower osmolarity than blood plasma and red blood cells *Hemolysis: the swelling and bursting of red blood cells because they cannot resist the increase in osmotic pressure when put into a hypotonic solution.