Chapter 12

Chapter 12 - Chapter 12 - Solutions solutions are critical...

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Chapter 12 - Solutions solutions are critical in both chemistry and biochemistry, since most reactions take place in solution (nearly every reaction in your body occurs in a water-based solution) practical applications as well - making a solution of a small amount of silver in gold (yes, solids can form solutions or alloys with other solids), the gold becomes harder and easier to cast because it melys at a lower temperature - adding ethylene glycol or antifreeze to water in a car radiator lowers the freezing temperature of pure water so the radiator does not freeze in the winter a solution is defined as a homogeneous mixture of two or more substances, either atoms, molecules, or ions - they can be liquids, solids, or gases Table 12.1 need to make solute - for a liquid solution, refers to the gas or solid that is dissolved in the liquid solvent, for other solutions, it is the substance in lesser amount (i.e., 20% methanol) nonreactive gases can mix in all proportions and are considered to be miscible - liquids that can mix with each other are also called miscible (water + alcohol), liquids that cannot are considered immiscible (oil + water) solubility refers to the amount of a substance (solute) that can dissolve in another substance (solvent) - this depends on the nature of the solute and solvent consider dissolution of 40.0 g of NaCl crystals in 100 ml of water at 20 C Figure 12.2 sodium and chloride ions leave the crystal and go into the aqueous solution - as time continues, concentration of ions in solution increases - ions move about randomly, some may hit the crystal that has yet to dissolve and stick and return to the solid state - as more salt dissolves and there are more ions in solution, more ions will collide with the salt and return to the crystalline state -if enough salt has been added, the concentration of ions in the solution will hit a maximum which is the solubility limit of NaCl in water at the specific temperature - the solution is called a saturated solution and there is now a dynamic equilibrium set up - this
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means that the rate of salt dissolving is exactly the same as salt returning to the solid state - the mass of undissolved salt remains constant - 36.0 g has dissolved and 4.0 g remains undissolved - so the solubility of NaCl in water at 20 C is 36.0 g/100 ml - if you add exactly 36.0 g to 100 ml of water, all of it would dissolve - anything less than 36.0 g/100 ml would give an unsaturated solution if you took a perfect cubic crystal of salt and added it to a saturated solution of salt, the shape of the crystal would change, but the total mass would not a supersaturated solution is one where more solute is dissolved than there should be (for a saturated solution) - the solubility of sodium thiosulfate Na2S2O3 in water is 231 g/100 ml at 100 C and 50 g/100 ml at room temperature - if you dissolve 231 g in 100 ml boiling water, then let it come to RT very slowly, the Na2S2O3 will stay in solution giving a supersaturated solution - this is not an
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This note was uploaded on 04/17/2008 for the course CH 101 taught by Professor Wolfman during the Spring '08 term at BC.

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Chapter 12 - Chapter 12 - Solutions solutions are critical...

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