CHM 105 & 106 UNIT THREE, LECTURE TWO 1 IN OUR PREVIOUS LECTURE WE WERE LOOKING AT TWO TYPES OF SPECIAL SOLUTIONS CALLED

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1 CHM 105 & 106 UNIT THREE, LECTURE TWO 1 CHM 105/106 Program 19: Unit 3 Lecture 2 IN OUR PREVIOUS LECTURE WE WERE LOOKING AT TWO TYPES OF SPECIAL SOLUTIONS CALLED ACID SOLUTIONS AND BASIC SOLUTIONS. WE TALKED ABOUT STRONG ACIDS AND WEAK ACIDS. WE DEFINED WHAT AN A CID WAS AND WHAT A BASE WAS, AND WE LL CONTINUE ON THEN TODAY TAKING A FURTHER LOOK AT SOME OF THOSE WEAK ACIDS WE BEGAN DISCUSSING I THE PREVIOUS LECTURE. JUST AS A QUICK REMINDER, THE STRENGTH OF AN ACID DEPENDS UPON ITS DEGREE OF IONIZATION, HOW MUCH IT IONIZES, OR DISSOCIATES WHEN WE PUT IT INTO THE SOLVENT, AND WE RE GOING TO BE LOOKING OF COURSE AT AQUEOUS SYSTEMS, SO WE RE SAYING HOW MUCH IT IONIZES WHEN WE PUT IT INTO A WATER SOLUTION. SO THE MORE IT FORMS IONS THE STRONGER THE ACID IS. SO WHEN WE TALK ABOUT THE VERY STRONG ACIDS THAT WE MENTIONED, HYDROBROMIC, HYDROCHLORIC, HYDROIODIC, NITRIC, SULFURIC, AND PERCHLORIC ACID, WE SAID THAT THESE ACIDS THEN ESSENTIALLY UNDERGO A 100% IONIZATION. BY THAT WE MEANT THAT THIS REPRESENTS ACID. WHEN WE PUT IT IN WITH WATER THE ACID GIVES ITS HYDROGEN ION, ITS PROTON TO THE WATER TO MAKE THE HYDRONIUM ION AND A NEGATIVE ION OF THE ACID, AND WE SAY THAT FOR STRONG ACIDS THIS IS NEARLY 100% EFFECT. IN OTHER WORDS, THE AMOUNT OF HYDRONIUM ION IN THE SYSTEM IS EQUAL TO THE MOLARITY OF THE STRONG ACID WHEN WE STARTED. SO IF WE DUMPED IN A MOLE OF ACID, ONE MOLE OF ACID WOULD FALL APART, WE WOULD GET ONE MOLE OF HYDRONIUM ION. IN THE CASE OF THE WEAK ACIDS, THEY DO NOT UNDERGO 100% DISSOCIATION IN WATER. WE AGAIN SHOW THE SAME TYPE OF CHEMICAL EQUATION, THE WEAK ACID DONATING A PROTON TO THE WATER TO FORM HYDRONIUM, AND THE NEGATIVE OR ANION OF THE ACID. BUT IN THIS CASE, THE HYDRONIUM ION CONCENTRATION IS EQUAL TO WHATEVER MOLARITY WE STARTED WITH TIMES THEN THE DEGREE OF IONIZATION. SO IF IT S 5% IONIZED, IF WE STARTED WITH A 1 MOLAR SOLUTION WE WOULD END UP WITH ONLY.05 MOLAR HYDRONIUM ION. WE THEN BEGAN LOOKING AT SOME WEAK ACIDS, AND TALKING A LITTLE BIT ABOUT SOM E OF THOSE,. WE MEN TIONED ACETIC ACID, WHICH IS THE ACID IN VINEGAR. BORIC ACID, WHICH WE MENTIONED CAN BE USED AS A MILD ANTISEPTIC OR

2 CHM 105 & 106 UNIT THREE, LECTURE TWO 2 EYEWASH, AND ALSO INSECTICIDE LIKE ROACH KILLER. WE TALKED A LITTLE BIT ABOUT NITROUS ACID, AND WE MENTIONED THE DIFFERENCE BETWEEN NITRIC ACID, HNO3, AND NITROUS ACID, HNO2. NITRIC ACID IS A STRONG ACID. NITROUS ACID IS A WEAK ACID. WE MENTIONED THE NITROUS ACID AND THE SULFUROUS ACID AS BOTH BEING CONTRIBUTORS TO ACID RAIN, AND THE LAST TOPIC IN THE CHA PTER TALKS ABOUT ACID RAIN AND WE WILL SPEND A LITTLE BIT OF TIME LOOKING AT THAT LATER. WE THEN LOOKED CLOSER AT PHOSPHORIC ACID, WHICH IS ALSO A WEAK ACID, AND ONE OF THE REASONS WE LOOKED CLOSER AT IT IS BECAUSE WE SAID THAT IT REPRESENTS WHAT WE CALL A POLYPROTIC ACID. A POLYPROTIC ACID, POLY OF COURSE MEANS MANY, AND PROTIC OR PROTON, SO MANY PROTON ACID IS WHAT WE RE SAYING, AND WHAT WE RE SHOWING HERE THEN IS THAT THE PHOSPHORIC ACID CAN ACTUALLY UNDERGO THREE DIFFERENT ACID REACTIONS, GIVING UP THREE DIFFERENT PROTONS TO THE WATER. SO THE FIRST CASE WE SHOWED GIVING UP TO WATER AND FORMING THE H2PO4, AND THEN SUBSEQUENTLY THE OTHER STEPS. AS WE INDICATED ALSO, PHOSPHORIC ACID IS VERY IMPORTANT INDUSTRIAL-WISE, IT S THE THIRD, EXCUSE ME, THE SEVENTH MOST IMPORTANT INDUSTRIAL CHEMICAL, PHOSPHORIC ACID. WE THE WERE LOOKING AT A FEW OF THE OTHER WEAK ACIDS IN THE LI ST, SUCH AS THE ACET IC ACID, AND WE NOTICED THIS GROUP RIGHT HERE, AND THE BENZOIC ACID WE NOTICE THIS GROUP RIGHT HERE, THE CITRIC ACID, WE NOTICE THIS GROUP RIGHT HERE, AND EACH OF THESE ACIDS CONTAIN A SIMILAR GROUP IN IT AND THAT PA RTICULAR GROUP IS CA LLED THE CARBOXYLIC ACID GROUP. THAT S OUR NEXT ORGANIC FUNCTIONAL GROUP, THEN WE RE TALKING ABOUT. SO FAR WE VE TALKED ABOUT HYDROCARBONS. WE TALKED ABOUT ALCOHOLS. WE TALKED ABOUT ETHERS UP TO THIS POINT. IN THIS CHAPTER NOW WE RE LOOKING AT THE CARBOXYLIC ACID GROUP WHICH HAS THIS GENERAL STRUCTURE. A HYDROCARBON GROUP R, ATTACHED TO THIS GROUP HERE, WHICH CAN BE WRITTEN. IF WE DO IT IN A STRUCTURAL FORMULA OF COURSE WE DRAW IT OUT LIKE THAT, AS WE SHOW HERE, OR IT CAN BE WRITTEN AS R-CO2H OR R-COOH. BOTH OF THESE MEAN THE SAME THING, OR AS I SAY, DRAW IT OUT IN A STRUCTURAL FORMULA IT LOOKS LIKE THAT. THE NAMING OF THE ACIDS AS I MENTIONED THE IUPAC NAMING OF THE ACIDS IS TO NAME THE HYDROCARBON

3 CHM 105 & 106 UNIT THREE, LECTURE TWO 3 CHAIN, CHANGE THE ENDING FROM E AND PUT IN OIC. SO CH4 IS METHANE. WHEN WE TAKE OFF THE HYDROGENS AND MAKE IT AN ACID IT BECOMES METHANOIC ACID. THE TWO CARBON HYDROCARBON IS CALLED ETHANE. IF WE TAKE OFF THE HYDROGENS AND MAKE IT AN ACID IT BECOMES ETHANOIC ACID. BUT MOST OF THE WEAK ACIDS THAT WE RE LOOKING AT ON THE CHART ACTUALLY HAVE MORE COMMON NAMES, A ND SO WE RE USUALLY GOING TO SEE A COMMON NAME FOR THE ACID, AND THOSE ARE THE ONES THAT WE LL TALK ABOUT A LITTLE BIT WHEN WE GO BACK TO THE TABLE. WE SPECIFICALLY MENTIONED THIS ONE, OXALIC ACID, BECAUSE WE NOTICE IT HAS TWO ACID GROUPS ON IT AND WE CALLED IT THEN A DICARBOXYLIC ACID. IT HAS TWO ACID GROUPS IN THE MOLECULE. OXALIC ACID AS I MENTIONED PREVIOUSLY IS A TOXIC CHEMICAL FOUND IN THE RHUBARB FAMILY OF PLANTS AND IS SORT OF A NATURAL PROTECTOR FOR THE PLANT FROM BEING EATEN BY ANIMALS. IT' ESPECIALLY CONCENTRATED IN THE LEAVES, MORESO THAN IN THE STALKS ET CETERA, WHICH TYPICALLY ARE USED TO MAKE JELLIES AND PIE. ALSO, IT DOES DECOMPOSE WHEN IT S HEATED, SO ANY RHUBARB PRODUCT THAT IS COOKED OF COURSE THE CARBOXYLIC ACID HAS ALREADY BEEN DESTROYED. QUICKLY LOOKING AT A FEW OTHERS THAN ON THE LIST, WE ALREADY MENTIONED ACETIC ACID IN VINEGAR, BENZOIC ACID IS USED AS A PRESERVATIVE. IF YOU LOOK AT BREAD OR JELLIES OR THINGS LIKE THAT YOU MAY SEE IT LISTED IN THERE. IT IS ACTUALLY THERE AS WHAT WE CALL AN ANTI-OXIDANT, SOMETHING THAT PREVENTS OXIDATION FROM OCCURRING, WHICH IS WHAT HAPPENS WHEN FOODS DECAY, THEY BECOME OXIDIZED, THEY REACT WITH THE OXYGEN IN THE AIR. THE BENZOIC ACID THEN INTERCEPTS THE OXYGEN SO THAT IT DOESN T REACT WITH THE FOOD AND PROTECTS THE FOOD THEN. SO IT S A FOOD PRESERVATIVE. OF COURSE CITRIC ACID WE RE FAMILIAR WITH, VITAMIN C, AND OF COURSE IT IS THE ACID THAT WE FIND IN CITRUS FRUIT, LEMON, LIMES, ORANGES, ET CETERA. FORMIC ACID IS FOUND IN ANT BITES, BITES. IS THAT RIGHT? DOESN T SEEM RIGHT, BUT ANT BITES, OKAY, THE BURNING SENSATION FROM AN ANT BITE IS USUALLY THE FORMIC ACID. LACTIC ACID IS FOUND IN MILK. SOMETIMES REFERRED TO AS MILK ACID, IT S THE THING THAT WHEN WE HAVE ACTUALLY IF FORMS AS MILK DECAYS OR SPOILS. WHEN YOU HAVE FRESH MILK IT HAS A SUGAR IN IT CALLED LACTOSE, AND LACTOSE REACTS WITH THE

4 CHM 105 & 106 UNIT THREE, LECTURE TWO 4 OXYGEN IN THE AIR AND IS CONVERTED TO LA CTIC ACID, AND SO MILK BECOMES SOUR AS IT SPOILS, AND WHEN YOU MAKE THE MILK ACID WHAT HAPPENS IS ALL OF THE PROTEIN STRUCTURES BEGIN TO CLUMP TOGETHER, AND SO WHAT HAPPENS IS YOU GET A CURDLING EFFECT. SO YOU GET DOUBLE, YOU GET THE SMELL OF THE SOUR PART OF THE MILK AND ALSO THEN THE CLUMPING TOGETHER OF THE PARTICLES. OKAY, OXALIC ACID WE VE ALREADY MENTIONED. TARTARIC ACID IS A CHEMICAL THAT IS MIXED WITH SODIUM HYDROGEN CARBONATE, OR BAKING SODA, AND THE COMBINATION OF THESE TWO IS REFERRED TO AS BAKING POWDER, AND THE PURPOSE OF THE TWO ARE THAT THE BAKING SODA REACTS WITH THE TARTARIC ACID AND THE BAKING SODA, THE HCO3 - REACTS WITH THE ACID, AND I M JUST GOING TO WRITE IT AS H-TAR, WE DON T NEED THE WHOLE FORMULA, THIS PROTON IS DONATED AND WE FORM H2CO3, CARBONIC ACID. CARBONIC ACID IS UNSTABLE AT WARM TEMPERATURES AND FALLS APART INTO WATER AND CARBON DIOXIDE. IT IS THE CARBON DIOXIDE FROM THE CARBONIC ACID THEN THAT FORMS THE BUBBLES IN THE BREAD DOUGH, OR IN THE CAKE WHEN YOU RE COOKING IT, A ND CAUSES IT TO RISE. SO THE BAKING POWDER IS REALLY PROVIDING US WITH AN ACID, TARTARIC ACID AND A BASE, SODIUM HYDROGEN CARBONATE. THE TWO REACT IN THE MOISTURE OF THE THING THAT YOU RE BAKING AND YOU GET THEN THE LEAVENING OR RAISING EFFECT. UNLEAVENED BREAD DOES N T HAVE THIS IN IT SO THERE IS NO CO2 TO FORM THESE LITTLE GASEOUS BUBBLES AND SO IT STAYS FLAT. SO IT DOESN T HAVE THE BAKING POWDER IN IT. BA KING POWDER IS A COM BINATION OF THE TWO. SO WE SEE THAT A LOT OF THE WEAK ACIDS A RE ORGANIC IN NATURE. THEY ARE CARBOXYLIC ACIDS. SO AS WE GO ALONG I M SURE WE WILL ENCOUNTER SOME ADDITIONAL TYPES OF WEAK ACIDS. NOW, WHATEVER WE SAID ABOUT ACIDS OF COURSE WE CAN SAY A SIMILAR THING ABOUT BASES. WE HAVE STRONG BASES, THAT MEANS BASIC COMPOUNDS THAT ACT AS BASES THAT ARE 100% IONIZED WHEN WE PUT THEM INTO WATER. THE STRONG BASES ARE SUCH THINGS AS SODIUM HYDROXIDE, POTASSIUM HYDROXIDE, BARIUM HYDROXIDE, CALCIUM HYDROXIDE THESE ARE CALLED STRONG BASES, AND THEY ALREADY HAVE THE O-H GROUP IN THEM. THE STRONG ACIDS USUALLY THEN IONIZE AND DIRECTLY GIVE US HYDROXIDE IONS, BUT WE ALSO HAVE A LOT OF WEAK BASES. ONE OF THE CHARACTERISTIC OF MOST OF THE

5 CHM 105 & 106 UNIT THREE, LECTURE TWO 5 WEAK BASES, THEY ARE ORGANIC AND THEY FA LL INTO ANOTHER ORGA NIC GROUP THAT WE CALL THE AMINES, A-M-I-N-E-S. THE CHA RACTERISTIC OF AN AMINE IS THAT IT CONTAINS A HYDROCARBON GROUP AND THEN A NITROGEN AND WHATEVER NUMBER OF HYDROGENS NECESSARY TO GIVE THREE THINGS ATTACHED TO THE NITROGEN. NOW, YOU LL NOTICE THAT I VE WRITTEN THREE DIFFERENT TYPES HERE. ACTUALLY WE CAN CONSIDER AN AMINE TO BE THEN AS A STARTING MATERIAL AND AMMONIA, WHICH HAS THIS STRUCTURE, AMMONIA IS THE STARTING WEAK BASE, AND THEN AS WE TAKE OFF A HYDROGEN AND PUT IN A HYDROCARBON GROUP IT BECOMES AN AMINE, BUT NOTICE THAT I VE GOT THREE EXAMPLES HERE, ONE AMINE IN WHICH WE HAD ONE HYDROGEN, ANOTHER AMINE IN WHICH WE HAVE TAKEN OF TWO HYDROGENS AND PUT ON TWO HYDROCARBON GROUPS, AND A THIRD ONE IN WHICH WE VE TAKEN OFF ALL THREE OF THE HYDROGENS AND PUT ON THREE HYDROCARBON GROUPS. WE CATEGORIZE THESE THEN AS THE FIRST ONE HERE, WE CALL THIS A PRIMARY AMINE. A PRIMARY AMINE HAS ONE HYDROGEN REPLACED. WE HAVE TWO HYDROGENS REPLACED, WE CALL THIS A SECONDARY AMINE, AND IF WE REPLACE ALL THREE HYDROGENS THIS IS REFERRED TO AS A TERTIARY AMINE. NOW, WE ALSO TALKED ABOUT PRIMARY, SECONDARY, AND TERTIARY ALCOHOLS BACK IN THE CHAPTER WHEN WE TALKED ABOUT THE ALCOHOL GROUP. A LITTLE DIFFERENT, HOWEVER. HERE IT S THE NUMBER OF HYDROGENS THAT WE HAVE REPLACED. IN THE ALCOHOL IT S STILL ALWAYS ONLY ONE O-H GROUP IN THE ALCOHOL, BUT IT S WHERE WE PUT IT IN THE MOLECULE. IF IT WAS ON THE END ATTACHED TO ONLY A SINGLE CARBON WE CALL IT A PRIMARY ALCOHOL. IF IT WERE IN A STRING OF CARBONS LIKE WE HAD THREE CARBONS AND WE HAD THE O-H HERE. WE CAL THAT THE SECONDARY ALCOHOL BECAUSE THE CARBON TO WHICH THE ALCOHOL WAS ATTACHED WAS DIRECTLY ATTACHED TO TWO OTHER CARBONS, AND A TERTIARY ALCOHOL WAS ONE IN WHICH THIS CARBON WAS ATTACHED TO EVEN A THIRD CARBON. BUT NOTICE A DIFFERENCE HERE IN THE CASE OF THE AMINES WERE ACTUALLY PUTTING IN MORE R GROUPS. IN THE CASE OF THE ALCOHOL WE RE STILL ONLY PUTTING IN ONE O-H, BUT IT S THE NUMBER OF CARBONS THAT THE CARBON IT IS ATTACHED TO DETERM INES WHETHER IT IS A PRIMARY OR A SECONDARY OR A TERTIARY ALCOHOL. NOW LET S TAKE A LOOK AT HOW AMMONIA AND WE

6 CHM 105 & 106 UNIT THREE, LECTURE TWO 6 CAN USE THIS TO REPRESENT ACTUALLY ANY ONE OF THOSE FOUR THAT WE HAD DRAWN UP THERE BECAUSE THEY W OULD ALL BEHAVE THE SAME. WHEN WE PUT AMMONIA IN WATER OR IF WE PUT IN THAT AMINE IT WOULDN T MAKE ANY DIFFERENCE IT REACTS WITH THE WATER AND WHAT DID WE SAY A BASE WAS? A BASE IS A PROTON ACCEPTOR, SO AS A BASE THE WATER IS GOING TO DONATE A PROTON TO THE AMMONIA AND WE RE GOING TO END UP WITH NH4 +. SO ONE OF THE TWO HYDROGENS HAS BEEN GIVEN TO THE AMMONIA. SO NOW WE HAVE FOUR HYDROGENS BUT IT S NOT GIVEN AS A HYDROGEN ATOM IT S GIVEN AS A HYDROGEN ION, A PROTON, AND WHAT ARE WE LEFT WITH? IF WE GIVE AWAY ONE OF THE HYDROGENS HERE WE JUST HAVE A HYDROGEN AND OXYGEN, BUT OF COURSE IT HAS THE MINUS CHARGE. BUT WE NOTICE THAT WHAT WE GET WHEN A WEAK BASE REACTS WITH WATER IS HYDROXIDE ION, WHICH IS THE SAME ION AS WE GOT WHEN WE DISSOLVED THE STRONG BASES. THE ONLY DIFFERENCE IS STRONG BASES GIVE US HYDROXIDE IONS DIRECTLY, WEAK BASES GIVE US HYDROXIDE IONS INDIRECTLY BY REA CTING WITH SOLVENT. ALRIGHT, THIS PARTICULAR ION HERE IS CALLED THE AMMONIUM ION, THE NH4 +, AND WHEN WE GET INTO THE CHAPTER ON NOMENCLATURE WE LL COME BACK AND TALK ABOUT AMMONIUM COMPOUNDS. AMMONIA IS NH3, AMMONIUM IS THE POSITIVE NH4 + ION. NOW WE HAD DICARBOXYLIC ACIDS, WE COULD ALSO HAVE DIAMINES. DIAMINES MEANS THAT WE HAVE TWO OF THES E NH GROUPS IN THE MOLECULE. IF WE HAD JUST TWO CARBONS WE COULD HAVE A CARBON AND A CARBON, AND THEN AN NH2 HERE AND AN NH2 OUT HERE ATTACHED. THE TWO DOESN T SHOW UP TOO WELL, AND THERE WOULD BE SOME OTHER HYDROGENS ON RIGHT THERE. IF WE DO THAT NOW WE SEE THAT WE HAVE THEN TWO AMINE GROUPS IN THE SAME MOLECULE AND THAT S CALLED A DIAMINE, A DIAMINE. AS A MATTER OF FACT, THIS PARTICULAR ONE, SEEING IT IS PRODUCED FROM ETHANE WOULD BE CALLED DI, EXCUSE M E, ETHYLENE FOR THE C2 GROUP, ETHYLENE DIAMINE WOULD BE THE WAY THAT WE WOULD NAME THAT PARTICULAR DIAMINE. A COUPLE OF INTERESTING DIAMINES GO INTO A GROUP OF CHEMICALS THAT OCCUR WHEN PROTEIN IN FOOD UNDERGOES DECAY, AND THESE ARE THE PTOMAINES. I M SURE ALL OF YOU HAVE HEARD OF PTOMAINE POISONING. PTOMAINE POISONING IS A CHEMICAL POISONING THAT S A TOXICITY THAT OCCURS WHEN THEN PROTEINS UNDERGO THE DECAYING PROCESS IN FOODS.

7 CHM 105 & 106 UNIT THREE, LECTURE TWO 7 WE FORM THEN THE PTOMAINES. TWO OF THESE ARE MENTIONED IN THE BOOK AND THEY HAVE THE NAME PUTRESCINE, AND I M NOT SURE I M SPELLING THAT CORRECTLY, BUT AND CADAVERINE. BUT ANYWAY, THESE ARE THE TWO CHEMICALS THAT WE DETECT FROM AN OLFACTORY STANDPOINT WHEN WE HAVE ANIMALS DECAYING. SO W HEN WE SMELL SOMETHING ROTTEN SMELLING TO US, ANIMAL THAT S DECAYING ALONG THE SIDE OF THE ROAD OR SOMETHING IT IS THESE TWO PARTICULAR DIAMINE SPECIES THAT ARE THE CULPRITS ARE THE SMELL, PUTRESCINE AND CADAVERINE, AND AS I SAY, AND THEY FALL INTO THE CATEGORY CALLED PTOMAINES AS SUCH. NOW, WHAT MIGHT BE POISONOUS TO US OR TOXIC TO US AS HUMANS IS NOT NECESSARILY TOXIC TO ALL ANIMAL AND BIRD SPECIES. AS A MATTER OF FACT, THERE ARE MANY ANIMALS THAT WILL EAT DEAD CA RCASSES THAT CONTAIN THE PTOMAINES AND HAVE NO ILL EFFECT WHATSOEVER. THE TOXICITY IS TO US PRIMARILY AS HUMANS. SO THERE ARE A LOT OF ANIMALS THAT CAN EAT DECAYING FLESH WITHOUT HAVING TOXICITY EFFECT TO THEM, SO IT IS VERY SPECIFIC TO HUMANS. ALRIGHT, SO AS I SAID, AS WE GO ALONG AND LOOK AT THE WEAK BASES AND WEAK ACIDS OF COURSE WE CAN KEEP IN MIND THE SAME TYPE OF CHEMISTRY IS INVOLVED, IT S A LEVEL OF DEGREE OF ASSOCIATION IN WATER. LET S LOOK HERE NOW QUICKLY JUST A GAIN AT THE REACTION. HERE S THE REACTION OF A WEAK ACID CALLED CYANIC ACID WITH WATER, AND THE CYANIC ACID THEN ACTS AS AN ACID BY DONATING A PROTON. IT S GOING TO GIVE THIS HYDROGEN TO THE WATER, AND SO THIS IS ACTING AS THE ACID. THE WATER, WHICH IS ACTING AS A PROTON ACCEPTOR IN THIS CASE, IS ACTING AS THE BASE. SO WATER HAS ACCEPTED A PROTON AND FORMED A HYDRONIUM ION AS WE CALLED IT AND THE NEGATIVE ION OF THE ACID. IN THE NEXT REACTION WE HAVE A WEAK BASE, AMMONIA, AND IT IS NOW REACTING WITH WATER, BUT IF IT IS ACTING AS A BASE IT MUST BE THE PROTON ACCEPTOR, AND SO IN THIS CASE, WATER AS WE SHOWED JUST A MOMENT AGO IS DONATING A PROTON TO THE AMMONIA, SO THE WATER IS ACTING AS THE ACID IN THIS CASE, AND WE FORM THE HYDRONIUM AND THE HYDROXIDE. NOW NOTICE THAT WATER HAS BEHAVED IN TWO DIFFERENT WAYS IN THESE TWO CHEMICAL REACTIONS. IN ONE CASE WATER HAS BEHAVED AS AN ACID, AND IN THE OTHER IT HAS BEHAVED AS A BASE. NOW WATER IS NOT THE ONLY CHEMICAL THAT CAN

8 CHM 105 & 106 UNIT THREE, LECTURE TWO 8 BEHAVE IN TWO DIFFERENT WAYS, AND CHEMICALS THAT CAN BEHAVE AS EITHER AN ACID OR A BASE, DEPENDING UPON THE CONDITION THEY RE PUT IN ARE REFERRED TO AS AMPHIPROTIC MATERIALS. AMPHIPROTIC MEANS THAT IT CAN ACT AS EITHER AN A CID OR A BASE DEPENDING UPON THE SYSTEM IT S PUT INTO. SO WATER IS AN AMPHIPROTIC MATERIAL BECAUSE IT CAN ACT AS EITHER AN ACID OR A BASE. WELL, ONE OF THE CHARACTERISTICS OF AMPHIPROTIC MATERIALS IS THEN THAT THEY CAN ACTUALLY REACT WITH THEMSELVES IN AN ACID-BASE MATTER. SO IF WE LOOK AT WATER MORE CLOSELY WHAT WE RE REALLY SAYING HERE IS THAT EVEN IN A SAMPLE OF PURE WATER SOME OF THE WATER MOLECULES ARE GOING TO REACT WITH SOME OF THE OTHER WATER MOLECULES AND THEY ARE GOING TO FORM SOME HYDRONIUM ION AND HYDROXIDE ION. NOW, PURE WATER IS NEUTRAL, IT S NOT AN ACID OR BASE. THE REASON IT S NOT AN ACID OR A BASE IS BECA USE IT IS ACTUALLY EQUALLY AN ACID AND A BASE. IT S NOT THAT IT ISN T EITHER ONE, BUT IT S THAT IT S EQUAL. IN OTHER WORDS, WE HAVE EXACTLY THE SAME AMOUNT OF ACID IONS, HYDRONIUM IONS FORMED AS WE DO HYDROXIDE IONS, AND EVEN THOUGH IT HAS SOME ACID CHARACTERISTIC IT LIKEWISE HAS SOME BASE CHARACTERISTIC AND SO OVERALL IT IS NEUTRAL. NOW, WE SAY THAT PURE WATER DOESN T CONDUCT AN ELECT RIC CURRENT. ONE OF THE CHARACTERISTICS OF WATER OF SOLUTIONS BEING ABLE TO CONDUCT WAS THAT THEY HAD IONS. ACTUALLY, WATER DOES, EVEN PURE WATER DOES CONDUCT A VERY VERY SMALL AMOUNT OF CURRENT BECAUSE IT DOES HAVE A VERY SMALL AMOUNT OF IONS IN IT. IN OTHER WORDS, WATER, PURE WATER, IS A VERY WEAK ELECTROLYTE, BUT WE CAN ACTUALLY MEASURE, WE CAN ACTUALLY MEASURE THAT IT DOES HAVE SOME ELECTRICAL CONDUCTIVITY. NOW, WHEN WE MEASURE THE AMOUNT OF CONDUCTIVITY AND DETERMINE THE CONCENTRATION OF THE IONS PRESENT, THAT S ONE OF THE METHODS THAT WE CAN USE TO DETERMINE ION CONCENTRATION IS ELECTRICAL CONDUCTIVITY. WHEN WE DO THAT W E FIND THAT THE CONCENTRATION, REMEM BER THE OTHER DAY WE MENTIONED THESE LITTLE BRACKETS AROUND SOMETHING MEA NS CONCENTRATION IN MOLES PER LITER, SO WHEN WE TAKE THE MOLARITY OF HYDRONIUM ION AND MULTIPLY IT BY THE MOLARITY OF THE HYDROXIDE ION, IN PURE WATER, WE FIND THAT IT HAS A NUM ERIC VALUE OF 1 X THAT S AT A

9 CHM 105 & 106 UNIT THREE, LECTURE TWO 9 PARTICULAR TEMPERATURE HOWEVER, SO WE SHOULD MENTION THAT THAT S ACTUALLY MEASURED AT 25 CELSIUS DEGREES, THEN WATER HAS THIS NUMERIC VALUE FOR THE TWO IONS. NOW SEEING THAT IN PURE WATER THE AMOUNT OF HYDRONIUM ION M UST BE EQUAL TO THE AMOUNT OF HYDROXIDE ION WE CAN THEN MAKE THE FURTHER STATEMENT THAT IN PURE WATER, HYDRONIUM ION WOULD BE EQUAL TO 1 X 10-7, AND THE HYDROXIDE ION WOULD BE EQUAL TO 1 X NOW, LET S GO BACK UP HERE JUST A SECOND AND LOOK AT THOSE TWO REACTIONS WE WERE LOOKING AT. NOTICE THAT WHEN I PUT HCN INTO WATER WHAT I HAVE DONE IS I HAVE INCREASED THE HYDRONIUM ION CONCENTRATION. THERE WAS ALREADY SOME THERE, BUT I HA VE NOW INCREASED THE HYDRONIUM ION CONCENTRATION THROUGH THAT REACTION, AND IF I INCREASE IT IT M EANS THEN THAT THE HYDRONIUM ION CONCENTRATION WILL BECOME GREATER THAN I M GOING TO ADD SOME IT S GOING TO GET GREATER THAN THAT. BUT THIS RELATIONSHIP ALWAYS HAS TO STAY THE SAME. SO IF THE HYDRONIUM ION GETS BIGGER WHAT HAS TO HAPPEN TOT HE HYDROXIDE ION? HAS TO GET SMALLER. THIS NUMBER IS A CONSTANT. THIS DOES NOT CHANGE, SO NO MATTER WHAT I DUMP INTO THE WATER, THIS TIMES THIS IS STILL GOING TO BE THIS. SO LET S JUST SUPPOSE THAT I WERE TO DUMP IN SOME HCN AND THAT I CHANGED THE HYDRONIUM NOW TO 1 X IF I DID THAT THE HYDROXIDE ION NOW MUST BE WHAT? 1 X 10-9, BECAUSE THAT TIMES THAT MUST STILL BE EQUAL TO WELL, THAT S ONE WAY WE CAN DEFINE A SYSTEM THAT IS AN ACID OR A BASE. IF THE HYDRONIUM ION CONCENTRATION IS GREATER THAN THE HYDROXIDE ION CONCENTRATION THE SYSTEM IS AN ACID. HYDRONIUM IS GREATER THAN HYDROXIDE THE SYSTEM IS AN ACID. OKAY, OR, WE CAN GO BACK DOWN HERE AND LOOK AT IT RELATIVE TO THIS STATEMENT ALSO, AND THAT S WHAT WE LL WRITE DOWN HERE NEXT. IF THE HYDRONIUM ION CONCENTRATION BECOMES GREATER THAN 1 X 10-7, WE JUST DID THAT WHEN WE PUT SOME HCN IN UP HERE WE MADE IT GREATER, IF THE HYDRONIUM ION IS GREATER THAN 1 X 10-7 WE CLASSIFY THE SOLUTION AS AN ACID. IF THE HYDRONIUM ION CONCENTRATION IS LESS THAN 10-7 HOW DO WE GET IT LESS THAN 10-7? WELL LET S LOOK AT THAT SECOND REACTION UP THERE. NOTICE THAT WHEN I PUT AMMONIA IN THE WATER WHAT DID I FORM? HYDROXIDE IONS, AND IF I INCREASE THE HYDROXIDE ION NOW, IF WE WENT

10 CHM 105 & 106 UNIT THREE, LECTURE TWO 10 BACK TO THIS REACTION HERE, IF I INCREASE THE HYDROXIDE ION, IF I MAKE IT 1 X 10-5 NOW WHAT S GOING TO HAPPEN TO THE HYDRONIUM ION THIS TIME? 1 X SO ADDING THE BASE MADE THE HYDROXIDE GREATER AND THE HYDRONIUM SMALLER. NOTICE THAT 10-9 NOW IS LESS THAN 10-7, AND THEREFORE THE SYSTEM IS A BASE. W E COULD USE EITHER HYDROXIDE OR HYDRONIUM TO IDENTIFY ACID OR BASE, BUT THE GENERAL AGREEMENT HAS BEEN TO EXPRESS ACIDITY IN TERMS OF THE HYDRONIUM ION, AND FINALLY, IF THE HYDRONIUM ION IS 1 X 10-7 THEN OF COURSE THE HYDROXIDE IS 1 X 10-7 AND WE RE TALKING A BOUT A NEUTRAL SYSTEM. IT HAS NEITHER ACID OR BASE QUA LITIES. NOW, WE CAN WRITE DOWN HYDRONIUM ION IN SOLUTIONS, IN VARIOUS FORMS. WE CAN SAY THAT FOR LET S SAY AN ACETIC ACID SOLUTION LIKE SAY ONE MOLAR ACETIC ACID, WHOOPS I VE GOT TOO MANY THERE, CH3COOH, THAT WOULD BE ACETIC ACID, ONE MOLAR ACETIC ACID SOLUTION GIVES ME 5.18 X 10-2 MOLAR HYDRONIUM ION. OR W E COULD SAY BRACKETS H30 + = 5.18 X REMEMBER THE BRACKETS MEAN MOLES PER LITER. THAT S ONE OF THE WAYS WE CAN EXPRESS THE ACIDITY IN A SOLUTION. YES, A QUESTION? (STUDENT RESPONSE- NOT AUDIBLE) OH, YES, THAT S WHAT IT S SUPPOSED TO BE. EXTRA LINE IN THERE, YES, THIS IS H30 +, OKAY. NOW, ANOTHER WAY THAT WE CAN DO THIS IS TO MATHEMATICALLY REARRANGE THIS, AND THIS IS A WAY THAT IT IS TYPICALLY DONE IS TO EXPRESS THE HYDRONIUM ION OR ACIDITY OF A SOLUTION IN TERMS OF A UNIT THAT WE CALL ph, AND WHAT DO WE MEAN BY ph? ph IS MERELY A MATHEMATICAL WAY THEN OF EXPRESSING THE HYDRONIUM ION CONCENTRATION. ph MATHEMATICALLY IS DEFINES AS MINUS THE LOGARITHM OF THE HYDRONIUM ION CONCENTRATION. IF ph IS LESS THAN 7.0 WHEN WE MAKE OUR CALCULATION, IF ph IS LESS THAN 7.0 THE SOLUTION IS AN ACID. IF THE CALCULATED NUMBER COMES OUT GREATER COMES OUT GREATER THAN 7 THE SOLUTION IS THE BASE, AND IF THE SOLUTION COMES OUT EXACTLY A ph OF 7 IT MEANS THAT WE ARE TALKING ABOUT A NEUTRAL CONDITION. SO LET S LOOK AT ONE CALCULATION HERE FOR CALCULATING A ph QUICKLY. LET S SUPPOSE THAT WE HAVE A HYDRONIUM ION CONCENTRATION OF 1.6 X 10-10, AND WE WANT TO CALCULATE THE ph. SO TO CALCULATE THE ph THEN WE RE GOING TO SAY THAT ph = -LOG 1.6 X NOW IN TERMS OF A CALCULATOR, HOW ARE WE GOING TO CARRY OUT THIS PARTICULAR MATHEMATICAL PROCESS? WELL, W E

11 CHM 105 & 106 UNIT THREE, LECTURE TWO 11 START THEN IF YOU LOOK ON YOUR CALCULATOR IF YOU HAVE IT WITH YOU THERE IS A BUTTON THAT SAYS LOG ON IT. SO THAT S THE FUNCTIONAL KEY THAT WE WANT TO LOOK FOR. WHAT WE RE GOING TO DO IS WE RE GOING TO PLUG IN THE NUMBER 1.6. NOW WE DON T PUT IN THE TIMES SIGN AND WE DON T PUT IN THE 10, EXPONENTIAL 10. SO WE LL HIT THAT LITTLE PLUS/MINUS BUTTON, NOT THE ADD AND SUBTRACT, BUT THAT COMBINATION PLUS SLASH MINUS, AND THEN 10. AND SO AT THAT POINT ON OUR CALCULATOR WE SHOULD SEE SOMETHING THAT LOOKS LI KE 1.6 AND THEN NEGATIVE 10, AND SOME MIGHT BE A LITTLE BIT SUPERSCRIPT, SOME MIGHT ACTUALLY JUST BE IN THE SAME NUMBER, BUT THAT S WHAT IT SHOULD LOOK LIKE. WHEN WE HAVE THAT, NOW WE JUST GO UP HERE AND PUNCH LOG AND THEN FINALLY WE NEED TO CHANGE THE SIGN ONCE AGAIN SO WE PUNCH THE +/- BUTTON, AND SO WHEN WE GET DONE HERE CALCULATING WE END UP WITH A VALUE OF 9.80 FOR THE ph. NOW KEEPING IN MID WHAT WE HAD UP HERE JUST A MOMENT AGO AS FAR AS THE ph AND THE TYPE OF SOLUTION THEREFORE FOR THIS PARTICULAR SOLUTION IN WHICH WE HAVE A HYDRONIUM ION OF 1.6 X 10-10, AND A ph CALCULATES OUT TO BE 9.80, ARE WE TALKING ABOUT A BASIC OR AN ACID SOLUTION? A BASIC, BECAUSE ph IS GREATER THAN 7, THEREFORE WE RE TALKING ABOUT A BASIC SOLUTION. NOW, ONE OF THE AREAS THAT SOMETIMES A LITTLE CONFUSING WHEN WE DO ph OR ARE WORKING FROM A ph GOING BACK TO HYDRONIUM ION IS THE NUMBER OF SIGNIFICANT FIGURES. THE NUMBER BEFORE THE DECIMAL IN A ph CALCULATED OR A LOGARITHMIC NUMBER HAS NOTHING TO DO WITH NUMBER OF SIGNIFICANT FIGURES, SO WE DON T EVEN CONSIDER IT IN DEALING WITH THE NUMBER OF SIGNIFICANT FIGURES. ONLY THE NUMBERS AFTER THE DECIMAL ARE COUNTED IN SIGNIFICANT FIGURES. SO WE SEE THAT IN THIS CASE 1.6 GAVE US TWO SIGNIFICANT FIGURES TO START WITH. WE SHOULD HAVE THEN TWO SIGNIFICANT, WE SHOULD HAVE TWO FIGURES AFTER THE DECIMAL POINT,.80. THIS 9 IS NOT COUNTED, THAT IS NOT ONE OF THE ONES COUNTED IN SIGNIFICANT FIGURES, ONLY THE ONES AFTER THE DECIMAL POINT. SO OFTEN IT CAN LOOK LIKE WE VE ADDED A SIGNIFICANT FIGURE IN OUR ANSWER. SOMETIMES WE MIGHT EVEN LOOK LIKE WE ADDED TWO. WHAT IF THE VALUE WAS 11.35? THAT S STILL ONLY TWO SIGNIFICANT FIGURES. THE 11 DOES NOT COUNT, THIS IS NOT PART OF SIGNIFICANT FIGURES.

12 CHM 105 & 106 UNIT THREE, LECTURE TWO 12 OKAY, SO NOT THAT WE LL WORRY A WHOLE LOT ABOUT THAT, BUT TRY AGAIN TO AT LEAST BE SOMEWHAT CLOSE TO BEING CORRECT ON SIGNIFICANT FIGURES. A QUESTION BACK THERE? (STUDENT RESPONSE NOT AUDIBLE) THE QUESTION WAS HOW DID I DETERMINE THE NUMBER OF SIGNIFICANT FIGURES I NEEDED IN MY FINAL CALCULATED NUMBER, AND YES, THIS GOES BACK TO THE 1 AND THE 6 HERE. REMEMBER, EXPONENTIAL POWERS OF 10 MERELY LOCATED DECIMAL POINTS, DOESN T HAVE ANYTHING TO DO WITH MEASURING QUANTITY. SO THE 1 AND THE 6 ARE THE ONLY THINGS THAT WERE MEASURED, AND SO 2 SIGNIFICANT FIGURES WOULD BE ALLOWED IN THE ANSWER. ALRIGHT, NOW WE CAN ALSO, WE LL COME BACK AND DO A COUPLE MORE EXAMPLE CALCULATIONS A LITTLE BIT LATER, BUT WE CAN THEN SORT OF LAY OUT A LITTLE CHART HERE OF ph S AND IN THE CENTER WE LL HAVE A ph OF 7, AND THAT IS NEUTRAL. AND AS WE GO FROM 7 UP TO 14 THAT MEANS THAT WE RE INCREASING IN ACIDITY, SO ANYTHING UP ON THIS SIDE IS A BASE. AS WE GO FROM 7 DOWN TO A ph OF 1, ACTUALLY A ph OF 0 WE GO DOWN THAT DIRECTION WE HAVE THEN AN ACID. AND THIS GOES BACK TO WHAT WE JUST SAID. IF ph IS GREATER THAN 7 IT IS A BASIC SOLUTION. IF ph IS LESS THAN 7 IT IS AN ACID SOLUTION. IF IT S 7 IT IS A NEUTRAL SOLUTION. LET S JUST TAKE QUICK LOOK HERE AT SOME ph S OF SOME COMMON MATERIALS THEN AND THINK ABOUT THEM IN TERMS OF ACIDITY OR BASIDITY. AND THESE ARE STARTING WITH THE MORE ACID WORKING DOWN TO THE MORE BASIC MATERIALS. WE SEE THAT A ONE MOLAR SOLUTION OF HYDROCHLORIC ACID, A STRONG ACID IS 100% DISSOCIATED. SO 1 MOLE PER LITER WOULD GIVE US 1 MOLE PER LITER OF HYDRONIUM ION, AND IF WE PLUGGED 1 INTO OUR CALCULATION MINUS THE LOG OF 1 WE LL COME UP WITH A VALUE OF 0, A ph OF 0. I DIDN T MENTION, CAN WE HAVE A ph LESS THAN 0? THE ANSWER IS YES WE CAN. IF WE HAVE SOMETHING THAT IS A MORE CONCENTRATED STRONG ACID, SAY IF WE HAD A 10 MOLAR HYDROCHLORIC ACID SOLUTION WE WOULD THEN HAVE 10 MOLES PER LITER OF HYDRONIUM ION AND IF WE PLUGGED THAT INTO OUR CALCULATOR IT LL COME OUT A NEGATIVE 1. SO YES, WE CAN HAVE A ph LESS THAN 0. WE CAN ALSO HAVE A ph GREATER THAN 14. FOR MOST PRACTICAL PURPOSES WE LIMIT OUR ph FROM 0 TO 14, BECAUSE THAT S WHERE MOST THINGS ARE GOING TO OCCUR. TOILET BOWL CLEANER, ph OF 1 TO 2, THAT MEANS PRETTY ACIDIC MOLES PER LITER OF

13 CHM 105 & 106 UNIT THREE, LECTURE TWO 13 ACID IN THERE. QUITE ACIDIC. WHY DO WE HAVE TOILET BOWLS SO ACIDIC? WELL ONE OF THE REASONS IS THAT PART OF THE MATERIAL THAT WE RE CLEARING OUT IS PROBABLY THE HARD WATER STAINS, THE CALCIUM CARBONATE, MAGNESIUM CARBONATE, IRON COMPOUNDS SUCH AS RUST, IRON HYDROXIDE, AND THE ACID WILL REMOVE THOSE, AND SO THAT IS PART OF THE PURPOSE THEN OF THE TOILET BOWL CLEANER, AND SO THEREFORE IT S ACIDIC. WELL, WE DON T HAVE TIME TO COVER ALL OF THIS IN THIS LECTURE, SO WE LL START BACK HERE IN OUR NEXT LECTURE AND LOOK AT A FEW MORE OF THESE AND GO ON AND LOOK AT SOME ADDITIONAL CALCULATIONS INVOLVING HYDRONIUM ION AND ph.