- WELCOME TO A VIDEO TUTORIAL
ON THE ACID-BASE CHEMISTRY OF CARBOXYLIC ACIDS,
AND ESPECIALLY LINKING IT TO WATER SOLUBILITY.
LET'S GET STARTED. ALL RIGHTY.
SO CARBOXYLIC ACIDS,
AS THE NAME WOULD IMPLY,
CAN LOSE A PROTON TO FORM CARBOXYLATES.
SO, WE'LL JUST WRITE A GENERIC CARBOXYLIC ACID HERE,
BECAUSE THE HYDROCARBON BACKBONE HAS NO INFLUENCE
ON THE ACIDITY OF THIS PROTON.
NOW, THESE ARE WEAK ACIDS,
SO I WILL SHOW AN EQUILIBRIUM ARROW.
AND SO, THIS IS OUR CARBOXYLATE AND OUR PROTON, RIGHT?
SO THERE'S QUITE A BIT OF LANGUAGE HAPPENING HERE.
LET'S MAKE SURE WE'RE ALL TOGETHER.
SO HERE'S OUR CARBOXYLIC ACID.
AND RECOGNIZING THAT IF WE HAVE THE HYDROCARBON CHAIN,
THERE'D BE A BUNCH OF HYDROGENS HERE.
BUT THIS IS THE ACIDIC PROTON.
AND SO, THAT WOULD BE DESCRIBED HERE, RIGHT?
H+ IS ALSO CALLED A PROTON.
AND THEN THE RESULTING ANION,
WE DESCRIBE AS A CARBOXYLATE. OKAY.
SO A BRIEF REVIEW OF WHY DO WE CALL H+ A PROTON, RIGHT?
SO LET'S THINK ABOUT A NEUTRAL HYDROGEN ATOM.
IF WE HAD A NEUTRAL HYDROGEN ATOM,
IT HAS ONE PROTON AND THEN THE MASS NUMBER IS ONE AS WELL.
RIGHT? SO THIS IS A Z,
OUR ATOMIC NUMBER, OUR NUMBER OF PROTONS.
AND THIS IS A, OUR MASS NUMBER,
WHICH IS PROTONS PLUS NEUTRONS.
AND SO, WE SEE THAT THERE ARE ZERO NEUTRONS.
AND OF COURSE, WE HAVE--
IF WE HAVE ONE PROTON AND IT'S NEUTRAL,
THERE'S THAT ONE ELECTRON FLOATING AROUND.
SO, LET'S LOOK AT WHAT--
WHAT'S THE ATOMIC STRUCTURE OF A HYDROGEN ION.
NOTICE THAT THE ONLY SUBATOMIC PARTICLES PRESENT
IN THE NEUTRAL ATOM WERE ONE PROTON AND ONE ELECTRON.
BUT WHEN WE FORMED THE HYDROGEN ION,
WE LOST THE ONE ELECTRON.
SO THE ONLY SUBATOMIC PARTICLES PRESENT ARE ONE PROTON.
ALL RIGHT.
SO, AS WE EXPLORE ACID-BASE CHEMISTRY MORE,
THE CONCEPT OF A PROTON BEING THE HYDROGEN ION
WILL SHOW UP AGAIN AND AGAIN.
LINGUISTICALLY,
WHEN WE'RE TALKING ABOUT THE CARBOXYLATE IONS,
IT'S REALLY AS SIMPLE
AS REPLACING THE "IC" ACID WITH "ATE."
SO, FOR EXAMPLE,
IF WE HAD A VERY COMMON, OOPS,
CARBOXYLIC ACID, THIS WOULD BE ACETIC ACID,
AND THEN WE WOULD LOOK AT THIS CARBOXYLATE
THAT WOULD BE ACETATE.
SO WE SEE HERE THAT THE IC ACID WAS REPLACED WITH ATE.
SO YOU ALREADY KNOW HOW TO NAME CARBOXYLIC ACIDS,
SO YOU'LL ALWAYS BE ABLE TO NAME THE CARBOXYLATE.
LET'S PRACTICE THAT FIRST BEFORE WE GET INTO THE--
DEEPER INTO THE CHEMISTRY.
SO, HERE I HAVE SHOWN YOU TWO IMPORTANT CARBOXYLIC ACIDS
THAT WE'LL SEE AS WE STUDY BIOCHEMISTRY,
PYRUVIC ACID AND LACTIC ACID.
HOWEVER, INSIDE THE BODY,
THEY WILL BE IN THEIR CARBOXYLATE FORM.
SO LET'S GO AHEAD AND DRAW THE SKELETAL LINE STRUCTURE
AND NAME THE RESULTING CARBOXYLATE.
SO, LOOKING AT THE STRUCTURE HERE,
I SHOWED ALL THE HYDROGENS TO HELP YOU PRACTICE AND EMPHASIZE
THAT THESE ARE THE ACIDIC HYDROGENS.
SO NOW, IF WE DRAW THIS AS THE CARBOXYLATE,
THIS WAS OUR CARBON HERE,
AND THEN WE HAVE THE KETONE.
AND SO, THIS WOULD BE
THE BOND-LINE STRUCTURE FOR PYRUVATE,
WHICH WE'LL LEARN MORE ABOUT PARTICULARLY
WHEN WE LOOKED AT GLYCOLYSIS,
THE BREAKDOWN OF SUGARS IN THE FUTURE.
AND THEN HERE'S LACTIC ACID.
AND SO, WE WILL SHOW THE CARBOXYLATE THERE AS WELL.
AND THEN THIS TIME, WE ALSO HAVE THREE CARBONS.
BUT HERE, WE HAD AN ALCOHOL GROUP INSTEAD OF A KETONE.
SO IF THIS IS CALLED LACTIC ACID,
THEN THE CARBOXYLATE WOULD BE REFERRED TO AS LACTATE.
ALL RIGHT.
SO THERE'S A LITTLE PRACTICE THERE WITH THE LANGUAGE.
AND THEN, LET'S LOOK AT ANOTHER EXAMPLE OF CARBOXYLATES
THAT WE RUN INTO ALL THE TIME.
CARBOXYLATES CAN FORM WATER-SOLUBLE SALTS
WITH SODIUM AND POTASSIUM IONS.
AND SO, HERE'S AN EXAMPLE.
WE HAVE POTASSIUM PROPANOATE.
SO WE RECOGNIZE POTASSIUM AS AN ALKALINE METAL.
IT WILL ALWAYS BE IN THE POSITIVE STATE.
AND THEN PROPANOATE, THERE'S OUR THREE CARBON.
SO WE'LL PUT.
AND THEN THERE'S THE "OATE."
SO WE KNOW THERE'S A CARBOXYLATE.
AND THEN THAT WOULD BE THREE CARBONS, ONE, TWO, THREE.
SO THAT WOULD BE THE SKELETAL LINE STRUCTURE
FOR POTASSIUM PROPANOATE.
ALL RIGHTY.
SO NOW, THAT WE UNDERSTAND THE LANGUAGE
TO DESCRIBE THE ACID-BASE CHEMISTRY OF CARBOXYLIC ACIDS,
LET'S PRACTICE DOING SOME REACTIONS HERE.
AND THESE ARE PRETTY USEFUL,
AND THEY'RE ALSO A GOOD EXAMPLE OF THE POWER OF CHARGE.
OKAY. SO LET'S GET THIS PROPERLY CENTERED.
GREAT. OKAY.
SO, LET'S DRAW THE SKELETAL LINE STRUCTURE FOR STEARIC ACID.
SO HERE'S OUR CARBOXYLIC ACID.
AND NOTICE THIS IS GOING TO BE A FATTY ACID.
WE HAVE A 16-CARBON CHAIN.
WELL, REALLY, IT'S A 17-CARBON CHAIN.
SO THE FIRST CARBON IS HERE, CARBON ONE.
THIS WOULD BE CARBON TWO, THREE,
FOUR, FIVE, SIX, SEVEN,
EIGHT, NINE, TEN, ELEVEN, TWELVE, THIRTEEN,
FOURTEEN, FIFTEEN, SIXTEEN.
AND THEN WE'D HAVE THE METHYL GROUP AT THE END.
SO HERE IS THE BOND-LINE STRUCTURE FOR STEARIC ACID.
WE WOULD DESCRIBE THIS AS AN EXAMPLE OF A FATTY ACID.
ALL RIGHT.
SO WOULD BE EXPECT STEARIC ACID TO BE WATER-SOLUBLE?
NO. RIGHT?
THE HYDROCARBON TAIL IS TOO LONG, RIGHT?
REMEMBER OUR "FOUR TO SIX" RULE.
IF WE HAVE A POLAR FUNCTIONAL GROUP,
IT CAN HELP FOUR TO SIX NON-POLAR CARBONS
TO BE WATER-SOLUBLE.
BUT ONCE WE HAVE 17 CARBONS, IT'S MUCH TOO LONG.
BUT HERE'S THE INTERESTING PART.
NOW, LET'S DRAW THE SKELETAL LINE STRUCTURE
FOR SODIUM STEARATE, RIGHT?
SO WE RECOGNIZE THAT AS THE CARBOXYLATE.
SO, THIS HYDROCARBON PART IS GOING TO BE THE SAME.
AND NOW WE'LL HAVE OUR CARBOXYLATE.
AND IN THIS EXAMPLE, WE HAVE A SODIUM COUNTERION.
NOW, WOULD YOU EXPECT THE CARBOXYLATE SALT
TO BE WATER-SOLUBLE?
AMAZINGLY, YES, IT IS.
WHY? RIGHT?
BECAUSE OF THE CHARGE ON THE CARBOXYLATE GROUP. RIGHT?
BECAUSE OF THE FULL, RIGHT,
NEGATIVE CHARGE ON THE CARBOXYLATE.
AND SO, CARBOXYLATE SALTS, ESPECIALLY FROM FATTY ACIDS,
ALL OF US BENEFIT FROM THOSE BECAUSE THEY'RE SOAPS.
SO SOAPS ARE WATER-SOLUBLE CARBOXYLATE SALTS.
SO HERE WE HAVE A DIAGRAM REPRESENTING.
SO HERE'S THE POLAR HEAD AND THEN THE NON-POLAR TAIL.
SO THIS POLAR HEAD, THIS IS GOING TO BE HYDROPHILIC.
AND ENOUGH THAT IT CREATES THE WATER SOLUBILITY.
SO HOW DO SOAPS GET US CLEAN?
WELL, THERE STILL IS THIS NON-POLAR,
GREASY TAIL, SO TO SPEAK.
AND SO, LET'S SAY THAT WE HAVE A GREASY STAIN IN--
ON OUR CLOTHES.
THE NON-POLAR HYDROPHOBIC TAILS WANT
TO INTERACT WITH THE GREASE,
RIGHT, VIA THE LONDON FORCE.
BUT THE POLAR HEADS ALL WANT TO INTERACT WITH THE WATER.
SO THEN WHAT HAPPENS IS, RIGHT,
SO THE NON-POLAR TAILS,
THIS IS WHAT LIFTS THE GREASE, RIGHT,
THIS INTERACTS WITH THE STAIN.
AND SO, WE RUB IN THE SOAP ALLOWING
THE HYDROPHOBIC TAILS TO INTERACT.
AND THEN, AS WE RINSE AWAY WITH THE WATER,
THE POLAR HEADS INTERACT WITH THE WATER
AND PULL AWAY THE GREASE.
SO, ALL OF OUR CLEANING OF SOAP,
THE UNDERLYING FORCE IN THAT IS INTERMOLECULAR FORCES.
AND THEN, IF YOU'RE WONDERING ABOUT SOAP SCUM,
REMEMBER THAT WITH CARBOXYLATE SALTS
THAT THEY'RE SOLUBLE WITH SODIUM OR POTASSIUM IONS.
BUT, IN HARD WATER,
IONS LIKE CALCIUM, MAGNESIUM, OR IRON,
THEY FORM INSOLUBLE CARBOXYLATE SALTS.
AND SO, IF WE WERE TO WRITE THE PHASES, RIGHT?
THE SODIUM SALT WOULD BE A Q, IT WOULD DISSOLVE IN WATER.
BUT THE CALCIUM SALT WOULD BE A SOLID, RIGHT?
AND THAT SOLID IS WHAT WE VIEW AS SOAP SCUM.
IF YOU'RE WONDERING ABOUT THE RATIO HERE, OF COURSE,
IF WE HAVE A MINUS ONE CHARGE AND A PLUS TWO CATION,
WE WILL NEED TWO OF OUR ANIONS TO CREATE THE NEUTRAL SOAP SCUM.
ALL RIGHTY.
SO THERE IS AN OVERVIEW OF THE ACID-BASE CHEMISTRY
OF CARBOXYLIC ACIDS AND,
REALLY, DIRECTLY HOW IT APPLIES TO WATER SOLUBILITY.
SO, PLEASE TAKE SOME TIME NOW TO WORK A FEW HOMEWORK QUESTIONS
TO REINFORCE YOUR UNDERSTANDING.