Chem121-Chapter-4-SH

Chem121-Chapter-4-SH - Chapter 4 Aqueous Reactions&...

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Unformatted text preview: Chapter 4: Aqueous Reactions & Solution Stoichiometry © R. Spinney 2009 Properties of Aqueous Solutions Solution : is a homogeneous mixture- common place for rxns to occur (reactants in a common unreactive environment)- solvent : is the liquid (in excess)- solute : is the solid dissolved in solvent- if solvent is H 2 O Æ aqueous solution Electrolytic Solutions Electrolytes : A substance which dissolves in water to give an electrically conducting solution by producing ions . – The movement of ions is responsible for the electric current that flows in the solution – Examples: Soluble ionic compounds and a few molecules. – (see fig 4.2 p 123) Nonelectrolytes : A substance which dissolves in water but do not conduct electricity! Usually Molecular compounds. Types of Solutions Ionic Compounds vs. Molecular Compounds Ionic Compounds vs. Molecular Compounds Ions in an ionic compound separate in water. Molecular compounds that do not break up into ions are solvated by the water. However, some molecular compound do form ions in water – they ionize. Properties of Aqueous Solutions (cont’d) NaCl – an ionic compound. NaCl( s ) → Na + ( aq ) + Cl- ( aq ) This process is dissociation ions of an ionic compound. The ions separate in water. Ethanol – a molecular compound. C 2 H 5 OH( l ) → C 2 H 5 OH( aq ) It dissolves but does not dissociate as it is a molecular compound! H 2 O Types of Electrolytes • Strong electrolytes : completely dissociate in solution, i.e. They exist in solution entirely as ions. • Weak electrolytes : dissolve in water to give a relatively small percentage of ions. These ions exist in equilibrium with the un-ionized substance. • The difference can be detected by placing electrodes in the solution. Properties of Aqueous Solutions (cont’d) Strong vs. Weak Electrolytes: HCl( g ) → H + ( aq ) + Cl- ( aq ) Process is called ionization (formation of ions) and solution is hydrochloric acid. Compare to equal concentration of acetic acid: CH 3 CO 2 H H + ( aq ) + CH 3 CO 2- ( aq ) Both solutions conduct electricity, but HCl does it much better. H 2 O H 2 O Properties of Aqueous Solutions (cont’d) Why? HCl is a molecular compound but it is a strong electrolyte because it dissociates (ionizes) 100% in solution. Acetic acid is a molecular compound but it is a weak electrolyte. It only partially ionizes in solution (the rxn can go both forward & reverse) ∴ the actual [H + ] & [CH 3 CO 2- ] in solution is << than from HCl Properties of Aqueous Solution (cont’d) Another common weak electrolyte is ammonia NH 3 , when dissolved in water it ionizes via: NH 3 ( aq ) + H 2 O( l ) NH 4 + ( aq ) + OH- ( aq ) Precipitation Reactions Metathesis rxns : common in aqueous solution where reactants exchange cations and anions to form new products....
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This note was uploaded on 04/04/2009 for the course CHEM 121 taught by Professor Wyzlouzil during the Spring '07 term at Ohio State.

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Chem121-Chapter-4-SH - Chapter 4 Aqueous Reactions&...

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