- WELCOME TO ACIDS AND BASES PART 1
IN THIS TUTORIAL, WE'LL INTRODUCE THE CONCEPT
OF ACID-BASE CHEMISTRY AND THEN GIVE YOU SOME PRACTICE,
PREDICTING THE PRODUCTS AND RECOGNIZING ACID-BASE REACTIONS.
LET'S GET STARTED.
ALL RIGHT. SO LET'S START WITH, WHAT IS AN ACID?
WELL, BACK A COUPLE CENTURIES AGO,
A GUY NAMED ARRHENIUS OFFERED A DEFINITION.
HE SAID THAT ACIDS ARE SUBSTANCES
THAT PRODUCE HYDROGEN IONS OR PROTONS WHEN DISSOLVED IN WATER.
THIS WAS A VERY CONTROVERSIAL IDEA
AND ARRHENIUS RECEIVED THE LOWEST PASSING GRADE
FOR HIS DOCTORATE.
10 YEARS LATER, HE RECEIVED THE NOBEL PRIZE
FOR THIS VERY QUESTIONABLE IDEA.
IT JUST GOES TO SHOW YOU WHAT THE FACULTY KNOW.
SO WHAT ARRHENIUS SAID IS THAT AN ACID IS A PROTON DONOR.
AND SO THEN THERE WILL BE THE COMPLIMENTARY ANION PRODUCED.
NOW, THE INTERESTING THING ABOUT ACIDS IS THAT THEY CAN COME
IN A STRONG FORM. AND SO WITH STRONG ACIDS,
WE WILL USE THE FULL REACTION ARROW TO THE RIGHT
TO SHOW COMPLETE IONIZATION.
IT ALSO COULD BE DESCRIBED AS DISSOCIATION.
THE ACID DISSOCIATES INTO THE IONS. ALL RIGHT.
SO WHEN IT'S A STRONG ACID, THIS HAPPENS COMPLETELY.
HOWEVER, BIOLOGICAL ACIDS ARE NOT STRONG ACID.
ACIDS ARE CARBOXYLIC ACIDS. THEY ARE WEAK ACIDS
AND SO THEY WILL UNDERGO AN EQUILIBRIUM REACTION
WHEN THEY ARE IN WATER.
AND SO, WE WILL GET THE CARBOXYLATE
AND THEN WE WILL GET THE HYDROGEN IONS
BUT THE FORWARD AND THE REVERSE REACTION WILL OCCUR TOGETHER.
SO TO KEEP THIS PROPER, WE'LL PUT THE AQS HERE.
SO WHEN WE TAKE AN ACID AND WE ADD IT TO WATER,
IT WILL PRODUCE HYDROGEN IONS,
STRONG ACIDS, COMPLETELY DISSOCIATE,
AND WEAK ACIDS, IT'S A PARTIAL REACTION.
AND WE SAY IT'S A PARTIAL REACTION
BECAUSE WE HAVE BOTH THE FORWARD AND REVERSE REACTIONS
OCCURRING TOGETHER.
ALL RIGHTY. SO THERE'S OUR INTRODUCTION TO ACIDS.
AND NOW, WE'LL LOOK AT BASES.
SO WHEN WE LOOK AT BASES, WE'RE LOOKING AT SUBSTANCES
THAT PRODUCE HYDROXIDE IONS.
OKAY. SO WHAT THIS TELLS US IS WE CAN START TO THINK
ABOUT WATER AS HOH, RIGHT?
WE CAN THINK OF WATER AS HYDROGEN IONS
AND HYDROXIDE IONS.
SO WHEN WE'RE LOOKING AT ACIDS, WE'RE FOCUSING ON
THE HYDROGEN IONS AND NOW WHEN WE LOOK AT BASES
AND BASES ALSO COME AS STRONG OR WEAK.
WHEN WE SEE THE HYDROXIDE, WE CAN RECOGNIZE THAT
AS A STRONG BASE.
AND SO JUST LIKE THE STRONG ACIDS,
IT WILL FULLY IONIZE IN WATER, RELEASING THESE HYDROXIDE IONS.
NOW, BIOLOGICALLY THOUGH, WITHIN OUR BODY,
WE DON'T HAVE STRONG BASES BUT WE DO HAVE WEAK BASES
AS A MEANS, RIGHT?
AND IT'S THAT LONE PAIR ON THE NITROGEN
THAT CREATES THE BASICITY.
SO WHEN WE ADD WHETHER IT'S A STRONG BASE OR A WEAK BASE,
WHEN WE ADD IT WITH WATER, WE PRODUCE HYDROXIDE IONS.
SO THAT MAY BE CONFUSING WHEN WE LOOK AT AMMONIA
BUT WHEN WE LOOK AT THE REACTION OF AN AMINE WITH WATER,
WE SEE THAT THE NITROGEN GRABS THE HYDROGEN ION
FROM THE WATER AND SO THE HYDROXIDE IONS ARE PRODUCED
INDIRECTLY THROUGH THE REACTION OF THE AMINE WITH WATER.
AND ONCE AGAIN NOTING A STRONG REACTION
GOES TO COMPLETION, 100%.
AND WEAK REACTIONS ARE PARTIAL OR EQUILIBRIUM REACTIONS
SO WE'LL HAVE THE FORWARD AND REVERSE REACTIONS
HAPPENING SIMULTANEOUSLY.
SO THIS WAS ONE OF OUR FIRST DEFINITIONS OF AN ACID.
LATER, IT WAS REFINED BY TWO GENTLEMEN, BRONSTED, LOWRY.
AND SO THEY DEFINED AN ACID AS A PROTON DONOR,
SO SIMILAR TO ARRHENIUS, RIGHT?
THINKING ABOUT PROTON AS H+.
AND THEN THEY DEFINED A BASE AS A PROTON ACCEPTOR,
SO STILL H+.
SO FOR EXAMPLE, IF WE LOOK AT THIS REACTION RIGHT HERE,
IF WE HAVE HYDROCHLORIC ACID WITH WATER,
HYDROCHLORIC ACID IS A STRONG ACID.
WE'LL TALK ABOUT THAT SOON. THEN IT DONATES ITS PROTON
TO THE WATER AND THEN WE HAVE THE CHLORIDE ION.
SO IF WE USE THE BRONSTED-LOWRY DEFINITION, RIGHT,
WE WOULD SAY THAT THE HYDROCHLORIC ACID
IS THE PROTON DONOR BECAUSE IT GAVE THE PROTON TO WATER
AND WE WOULD DESCRIBE THE WATER AS THE BASE
BECAUSE IT ACCEPTED THE PROTON FROM THE ACID.
AND SO, WE WILL HAVE A FOLLOW-UP TUTORIAL
THAT WILL GO MORE IN DEPTH INTO THE BRONSTED-LOWRY DEFINITION.
AT THIS POINT, WE JUST WANT TO INTRODUCE THE CONCEPTS.
SO NOW, LET'S PRACTICE PREDICTING THE PRODUCTS
OF ACID-BASE REACTIONS ON THE NEXT PAGE.
SO IF WE LOOK HERE, FIRST,
WE'LL PRACTICE WHERE I'VE GIVEN YOU THE REACTANTS
AND THE PRODUCTS,
LET'S START THERE AND LABELING.
SO WE LOOK AT THE REACTANTS AND THE PRODUCTS
AND WE HAVE TO NOTE HOW THEY'VE CHANGED.
SO WE SEE HERE THAT THERE'S A HYDROGEN ION PRESENT
AND NOTICE THAT IT'S BEEN LOST.
AND WHEN WE LOOK AT SODIUM HYDROXIDE, RIGHT,
WE WANT TO RECOGNIZE THAT AS SODIUM IONS AND HYDROXIDE IONS,
SO NOTICE THAT THE SODIUM ION IS SIMPLY A SPECTATOR ION.
WE HAVE SODIUM IONS FLOATING AS A REACTANT.
AND THEN WE HAVE SODIUM IONS AS A PRODUCT.
SO THIS--WE CAN IGNORE THE SODIUM IONS.
SO THEN WE CAN FOCUS ON THE HYDROXIDE
AND NOTICE WHAT'S HAPPENED TO THE HYDROXIDE, RIGHT?
IT GAINED H+, RIGHT?
IT GAINED A HYDROGEN ION.
SO THE HYDROXIDE WAS THE BASE, RIGHT?
IT GAINED OR ACCEPTED THE HYDROGEN ION
AND THIS LONG, CHAINED CARBOXYLIC ACID IS THE ACID,
RIGHT, BECAUSE IT DONATED H+, RIGHT?
AND SO MAYBE INSTEAD OF GAINED, WE COULD SAY ACCEPTED,
SO THAT WE USE THE LANGUAGE OF BRONSTED AND LOWRY.
ALL RIGHT. LET'S TRY ANOTHER ONE.
OKAY. SO WE LOOK AT THIS NEXT REACTANT
AND WE SEE THAT IT'S NEUTRAL AND WHEN WE LOOK AT THE PRODUCT,
WE SEE IT HAS GAINED AND ACCEPTED A PROTON
SO WE CAN LOOK RIGHT AWAY HERE AND SAY THAT THIS COMPOUND
IS OUR BASE WHICH WE KNOW TO EXPECT.
AMINES ARE WEAK BASES, IT ACCEPTED A PROTON, H+.
AT THE SAME TIME, IF WE LOOK HERE AT OUR HYDROCHLORIC ACID,
WE CAN START TO THINK OF HYDROCHLORIC ACID AS H+
AND CO- AND WHAT DO YOU KNOW, RIGHT, WHAT HAPPENED?
RIGHT, IT DONATED H+. SO THIS IS OUR ACID
WHICH THE NAME GIVES AWAY,
THE HYDROCHLORIC ACID TAKES THE ROLE OF ACID
AND AMINE TAKES THE ROLE OF BASE.
THE ACID DONATES A PROTON. SO SINCE IT'S DONATED THE PROTON
IT'S LOST AND THE BASE ACCEPTS THE PROTON.
ALL RIGHTY. NOW, LET'S CRANK IT UP A LITTLE BIT.
ALL RIGHT. LET'S SEE HOW WELL YOU'RE DOING.
SO NOW, GIVEN TWO REACTANTS, PREDICT THE PRODUCTS.
SO WE RECOGNIZE OUR CARBOXYLIC ACID RIGHT THERE.
THERE'S THE IONIZABLE PROTON SO THERE'S OUR ACID.
AND THEN OF COURSE SODIUM HYDROXIDE,
WE CAN RECOGNIZE HYDROXIDE AS OUR BASE.
SO WHEN WE GO TO PREDICT THE PRODUCTS,
THE ACID DONATES A PROTON SO THE PROTON IS LOST TO THE ACID
AND THE BASE GAINS THE PROTON.
SO YOU CAN THINK OF IT THAT WAY OR WE CAN JUST WRITE IT AS H20
AND THEN THE SODIUM ONCE AGAIN IS FLOATING AROUND
AS A SPECTATOR ION, KEEPING OUR CHARGE BALANCED
BETWEEN THE REACTANT SIDE AND THE PRODUCT SIDE.
OKAY. AND THEN, LAST BUT NOT LEAST, WHEN WE SEE AMINES,
WE INSTANTLY RECOGNIZE THEM AS WEAK BASES
SO THEY'RE THE H+ ACCEPTOR.
AND OF COURSE, WE SEE THE HYDROCHLORIC ACID AS THE ACID
AND THERE'S OUR BASE.
AND SO NOW WE CAN PREDICT THE PRODUCTS.
SO NOTICE WE START TO LIKE THE R GROUP
BECAUSE THEN WE DON'T HAVE TO WRITE ALL THIS DETAIL HERE
FOR THINGS THAT AREN'T CHANGING.
SO THERE'S OUR NITROGEN, SO THERE'S THE METHYL GROUP,
THERE WAS THE ORIGINAL HYDROGEN AND THEN HERE IS THE HYDROGEN
THAT WAS GAINED--ACCEPTED FROM THE ACID
AND THEN WE WOULD HAVE OUR CHLORIDE
AND THEN OF COURSE WE RECOGNIZE, IN THIS CASE,
WE COULD RECOGNIZE THIS AS THE AMMONIUM SALT.
OKAY. SO THAT CONCLUDES THE INTRODUCTION
TO ACID-BASE CHEMISTRY,
PLEASE TAKE TIME NOW TO WORK A FEW HOMEWORK PROBLEMS
TO REINFORCE YOUR UNDERSTANDING.