CHEM 140 Chapter 9: Chem 140- Ch 9

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Chemistry and Biochemistry
CHEM 140
P Pierce

Chapter 9: Solutions Book Notes Heading: Notes: Solutions ● A solution is a homogeneous mixture where the solute is uniformly distributed in a substance called the solvent ● Particles of the solute are evenly dispersed among the molecules of the solvent ● The solution that forms is in the same physical state as the solvent ● Water is known as the universal solvent and is very common in nature ● O-H bond is very polar, water is a polar solvent because the O atom has a partial negative charge and the H atom has a partial negative change. ● Water is a polar solvent ● Hydrogen bonds occur between molecules where partially positive hydrogen atoms are attracted to partially negative atoms Formation of Solutions ● Interactions between solute and solvent determine whether a solution will form ● Energy is needed to separate solute and solvent particles ● Energy is released as solute particles move in the solvent to form a solution ● Attraction accounts for the first separation and this will occur when solute and solvent have similar polarities- like dissolves like ● Without that likeness that leads to energy of separation of particles, there isn’t enough energy to form solution Solutions with Ionic and Polar Solutes ● When NaCl crystals are placed in water, partially negative oxygen atoms in water molecules attract positive Na+ ions and the partially positive hydrogen atoms attract negative Cl- ions ● When Na+ and Cl- form a solution, hydration occurs when water molecules surround each ion, which stops their attraction to other ions ● Strong solute solvent attraction provide the energy needed to form the solution Solutions with Nonpolar Solutes ● Nonpolar solutes will not dissolve in water or any other polar solvent. They will dissolve in nonpolar solvent and form a solution with them ● There are almost no attractions between the particles of a nonpolar solvent and a polar solvent Electrolytes and Nonelectrolytes ● Solutes can be classified as: Electrolytes dissolve in water and the process of dissociation separates ions out and form solutions that can conduct electricity. ● Nonelectrolytes dissolve in water and do not separate into ions and do not conduct electricity ● Strong electrolyte=NaCl. There is a 100% disassociation of the NaCl into ions. ● When writing an equation for a disassociation reaction, the charges must balance ● Weak electrolyte= a compound that dissolves in water mostly as molecules. Not many of the dissolved solute molecules actually go through ionization and form ions. There are only a small number of ions in the solution ● Weak electrolyte solutions do not conduct electricity as effectively as strong electrolyte solutions ● Forward and reverse reactions of molecules to ions and back again are shown by two arrows between the reactant and product ● Nonelectrolytes dissolve as molecules and do not ionize, does not conduct electricity Equivalents ● We measure each ion in a mixture of electrolytes in terms of an equivalent, which is the amount of that ion equal to one mole of positive or negative charge Na+=1 eq Cl-=1 eq ● In all solutions the charge of the positive ion is always balanced by the charge of the negative ion ● Expressed in milliequivalents per liter. 1Eq=1000mEq Solubility ● Solubility is used to describe the amount of solute that can dissolve in a given amount of solvent ● Type of solute/solvent and temp affect the solubility ● Solubility expressed in grams of solute/100g solvent ● The maximum amount of solute that can be dissolved at a given temperature ● Unsaturated solution is when the solvent can still dissolve more solute ● A solution that has dissolved all the solute possible is called a saturated solution ● When a solution is saturated, the rate at which the solute dissolves becomes equal to the rate where solid forms, recrystallization ● Arrows going back and forth in chemical equal between the two equal rates ● To obt
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