EQUIPPED WITH HIS FIVE SENSES, MAN EXPLORES THE UNIVERSE AND CALLS THESE ADVENTURES SCIENCE

A SOLUTION THAT HAS ALL OF THE SOLID DISSOLVED IN IT THAT WILL DISSOLVE (AT THE SOLUBILITY LIMIT) IS SAID TO BE SATURATED. IF LESS IS DISSOLVED THAN IS NEEDED TO FORM A SATURATED SOLUTION, WE SAY THAT THE SOLUTION IS UNSATURATED. IF WE HAVE MORE SOLUTE DISSOLVED THAN IS NEEDED FOR A SATURATED SOLUTION, WE SAY THAT THE SOLUTION IS SUPERSATURATED. MOST SOLIDS ARE MORE SOLUBLE AT HIGHER TEMPERATURES THAN AT LOWER TEMPERATURES, SO WE COULD DISSOLVE A SOLID IN A SOLVENT AT HIGH TEMPERATURE, AND THEN WE COULD COOL IT TO FORM A SUPERSATURATED SOLUTION.

IN CONTRAST TO SOLIDS, THE SOLUBILITY OF GASES USUALLY DECREASES WITH INCREASE IN TEMPERATURE. WHERE DO YOU SEE EXAMPLES OF THIS?

THE SOLUBILITY OF LIQUIDS AND SOLIDS IN A LIQUID SOLVENT IS NOT AFFECTED VERY MUCH BY PRESSURE. THIS IS NOT TRUE WITH GASES. AS THE PRESSURE ON A GAS ABOVE THE SURFACE OF A LIQUID INCREASES, THE SOLUBILITY OF THE GAS IN THE LIQUID INCREASES. WE CAN REASON THIS OUT WHEN WE THINK ABOUT WHAT IS HAPPENING AT EQUILIBRIUM – THE GAS MOLECULES WOULD BE LEAVING THE SURFACE OF THE LIQUID AT THE SAME RATE THAT GAS MOLECULES IN THE GAS COLLIDE WITH AND ENTER THE LIQUID. AS YOU COMPRESS THE GAS ABOVE THE SURFACE, YOU ARE INCREASING THE NUMBER OF GAS MOLECULES PER UNIT VOLUME IN THE GAS, SO YOU WOULD HAVE MORE COLLISIONS WITH THE SURFACE.

THIS EFFECT IS STATED IN HENRY’S LAW: THE SOLUBILITY OF A GAS INCREASES IN DIRECT PROPORTION TO ITS PARTIAL PRESSURE ABOVE THE SOLUTION. S g = kP g where S g is the solubility of the gas k is a proportionality constant P g is the partial pressure of the gas BOTTLERS OF BEER AND SOFT DRINKS USE THIS EFFECT. THEY BOTTLE THE BEVERAGES AT PRESSURES GREATER THAN ATMOSPHERIC PRESSURE. SO, YOU GET BUBBLES WHEN THE BOTTLE IS OPENED. HOW DOES HENRY’S LAW APPLY TO SCUBA DIVERS?

Sometimes, people are beautiful. Not in looks. Not in what they say. Just in who they are. -Markus Zusak

IT IS USEFUL WHEN WE WRITE EQUATIONS FOR REACTIONS THAT OCCUR IN AQUEOUS SOLUTION TO INDICATE IF THE REACTANTS AND PRODUCTS ARE IONS OR MOLECULES OR IONIC SOLIDS. LET’S CONSIDE THE FOLLOWING EXAMPLE: Pb(NO 3 ) 2 (aq) + 2KI (aq)  PbI 2 (s) + 2KNO 3 (aq) Pb(NO 3 ) 2, KI, and KNO 3 ARE ALL IONIC, SO WE COULD WRITE THE EQUATION AS: Pb +2 (aq) + 2NO 3 - (aq) + 2K + (aq) + 2I - (aq)  PbI 2 (s) + 2K + (aq) + 2NO 3 - (aq) THIS IS CALLED A COMPLETE IONIC EQUATION.

IF YOU WILL NOTICE, THERE ARE CERTAIN IONS THAT ARE THE SAME ON BOTH SIDES OF THE EQUATION – NO 3 -, K +. THESE ARE CALLED SPECTATOR IONS. SPECTATOR IONS DO NOT PARTICIPATE IN THE REACTION, AS THEY DO NOT CHANGE FROM ONE SIDE OF THE EQUATION TO THE OTHER. WE CAN REWRITE THE EQUATION FOR THE REACTION, LEAVING THE SPECTATOR IONS OUT. THIS IS CALLED THE NET IONIC EQUATION. Pb +2 (aq) + 2I - (aq)  PbI 2 (s) NOTE: IF EVERY ION IN A COMPLEX REACTION EQUATION IS A SPECTATOR ION, NO REACTION OCCURS.

IF YOU WILL NOTICE, THERE ARE CERTAIN IONS THAT ARE THE SAME ON BOTH SIDES OF THE EQUATION – NO 3 -, K +. THESE ARE CALLED SPECTATOR IONS. SPECTATOR IONS DO NOT PARTICIPATE IN THE REACTION, AS THEY DO NOT CHANGE FROM ONE SIDE OF THE EQUATION TO THE OTHER. WE CAN REWRITE THE EQUATION FOR THE REACTION, LEAVING THE SPECTATOR IONS OUT. THIS IS CALLED THE NET IONIC EQUATION. Pb +2 (aq) + 2I - (aq)  PbI 2 (s) NOTE: IF EVERY ION IN A COMPLEX REACTION EQUATION IS A SPECTATOR ION, NO REACTION OCCURS.

Ca Cl - + 2Na + + CO 3 -2 == CaCO 3 (s) + 2Na + + 2Cl - GETTING RID OF SPECTATOR IONS, THE NET IONIC EQUATION IS Ca +2 + CO 3 -2 == CaCO 3 (s) MOLECULAR IONS YOU SHOULD KNOW: OH - HYDROXIDE ION CO 3 -2 CARBONATE ION SO 4 -2 SULFATE ION NO 3 - NITRATE ION NH 4 + AMMONIUM ION