<body bgcolor="#FFFFFF"> <p><B>Reactions</B> which occur in solution</p> <p><A HREF="#precip_Anchor"><B>Precipitation</B></A><B> </B>reactions<B> </B></p> <p><A HREF="acid_base_ANCHOR"><B>Acid-base</B></A> neutralization reactions</p> <p><B>Redox</B> Reactions</p> <p><A HREF="../gen_chem.html" target="top">return to GenChem Home Page</A></p> <p> <HR> <A NAME="precip_Anchor"></A></p> <p><B>Precipitation reactions</B>&emdash;not all ionic compounds are soluble in water. If PbSO<SUB>4</SUB> is added to water none of the lead(II)sulfate will dissolve. The interaction between Pb<SUp>2+</SUp> and SO<SUB>4</SUB><SUp>2-</SUp> is simply stronger than the attraction of the water to either the Pb<SUp>2+</SUp> or SO<SUB>4</SUB><SUp>2-</SUp> (<font size="-1">Both enthalpy and entropy play a roll. We will discuss entropy and lattice energy second semester. We will dissus enthalpy and bond energy later this semester</font>).</p> <p>Simple Rules for the Solubility of Salts in Water</p> <OL> <LI>Most nitrate (NO<SUp>3-</SUp>) salts are soluble.</LI> <LI>Most salts containing the alkali metal ions (Li<SUp>+</SUp>, Na<SUp>+</SUp>, K<SUp>+</SUp>, Cs<SUp>+</SUp>, Rb<SUp>+</SUp>) and the ammonium ion (NH<SUB>4</SUB><SUp>+</SUp>) are soluble.</LI> <LI>Most chloride, bromide and iodide salts are soluble. Notable exceptions are salts containing the ions Ag<SUp>+</SUp>, Pb<SUp>2+</SUp>, and Hg<SUB>2</SUB><SUp>2+</SUp>.</LI> <LI>Most sulfate salts are soluble. Notable exceptions are BaSO<SUB>4</SUB>, PbSO<SUB>4</SUB>, HgSO<SUB>4</SUB>, and CaSO<SUB>4</SUB>.</LI> <LI>Most hydroxide salts are only slightly soluble. The important soluble hydroxides are NaOH and KOH. The compounds Ba(OH)<SUB>2</SUB>, Sr(OH)<SUB>2</SUB>, and Ca(OH)<SUB>2</SUB> are marginally soluble.</LI> <LI>Most sulfide (S<SUp>-2</SUp>), carbonate (CO<SUB>3</SUB><SUp>2-</SUp>), chromate (CrO<SUB>4</SUB><SUp>2-</SUp>), and phosphate (PO<SUB>4</SUB><SUp>-3</SUp>) are only slightly soluble.</LI> </OL> <p>If two solutions are mixed together it is possible that two ions could combine to form an insoluble ionic complex.</p> <p> </p> <p>A solution of silver nitrate is combined with a solution of sodium chloride. The resulting solution contains Na<SUp>+</SUp>, Ag<SUp>+</SUp>, Cl<SUp>+</SUp>, and NO<SUB>3</SUB><SUp>-</SUp>, but AgCl is not soluble in water. Since Ag<SUp>+</SUp> is now in solution with Cl<SUp>-</SUp> the two will combine to form AgCl, and the AgCl will precipitate from solution.</p> <blockquote>The reaction can be described in a number of ways</blockquote> <OL> <LI>A "<I>molecular</I> " equation could be used: <center><IMG SRC="reactions_in_solution_gifs/molecular_agcl.gif" WIDTH=345 HEIGHT=28 ALIGN=bottom></center></LI> <LI>  A <I>"complete ionic</I> " equation could be used: <center><IMG SRC="reactions_in_solution_gifs/complete_ionic_agcl.gif" WIDTH=506 HEIGHT=31 ALIGN=bottom></center></LI> <LI>A <I>"net ionic</I> " equation could be used. <center><IMG SRC="reactions_in_solution_gifs/net_ionic_agcl.gif" WIDTH=227 HEIGHT=31 ALIGN=bottom></center> <p>Net ionic equations are found by writing the full equation and then eliminating the spectator ions; spectator ions are ions that do not participate in the reaction. In the example above Na<SUp>+</SUp>(aq) and NO<SUB>3</SUB><SUp>-</SUp> are present as both products and reactants. Since Na<SUp>+</SUp>(aq) and NO<SUB>3</SUB><SUp>-</SUp> do not participate in the reaction they are called spectator ions.</p></LI> </OL> <p><A NAME="acid_base_Anchor"></A> <HR> </p> <p><A HREF="../gen_chem.html">return to GenChem Home Page</A></p> <p></p> </body>