- WELCOME TO THE VIDEO TUTORIAL
ON INTERMOLECULAR FORCES AND SOLUTIONS.
SO, IF WE THINK BACK ON WHAT WE'VE STUDIED THIS SEMESTER,
WE KNOW THAT MATTER IS DIVIDED INTO PURE SUBSTANCES
AND MIXTURES.
AND SO, NOW, WE REALLY WANT TO FOCUS ON THE MIXTURE PART
AND SPECIFICALLY ON HOMOGENEOUS SOLUTIONS
BECAUSE THAT'S WHAT WE'RE GOING TO BE
WORKING WITH QUITE A BIT, RIGHT?
SO, REMEMBERING THAT A HETEROGENEOUS MIXTURE,
THE COMPONENTS ARE UNEVENLY
DISTRIBUTED THROUGHOUT THE MIXTURE
AND WE'RE GOING TO HAVE TWO OR MORE PHASES.
WITH A HOMOGENEOUS MIXTURE,
THE COMPONENTS ARE EVENLY DISTRIBUTED
THROUGHOUT THE MIXTURE.
SO, WE WILL HAVE ONE PHASE.
NOW, WHETHER OR NOT WHEN WE MIX TWO SUBSTANCES,
THEY FORM A HETEROGENEOUS MIXTURE OR A HOMOGENEOUS MIXTURE
IS RELATED TO INTERMOLECULAR FORCES.
AND I'LL DEVELOP THAT CONCEPT MORE ON THE NEXT PAGE.
SO, WE'RE GOING TO BE LOOKING AT THE HOMOGENEOUS MIXTURE,
RIGHT, OF SOLUTIONS.
AND WHEN WE DESCRIBE A SOLUTION,
THE SOLUTE IS THE SUBSTANCE PRESENT
IN THE SOLUTION IN A LESSER AMOUNT.
THIS IS USUALLY WHAT WE'RE INTERESTED IN.
THIS IS OUR REACTANT, RIGHT,
OR IT COULD BE THE MEDICINE
THAT WE WANT TO GIVE TO THE PATIENT.
AND THEN, THE SOLVENT IS THE SUBSTANCE PRESENT
IN THE GREATEST AMOUNT.
AND BASICALLY, THIS IS NEEDED
TO DISSOLVE THE SOLUTE.
AND SO FOR OUR COURSE,
WE KNOW WE'RE LOOKING AT MOSTLY WATER-BASED SOLUTIONS.
SO, NOW, THAT WE'VE CONNECTED OUR OVERVIEW
OF MATTER TO SOLUTIONS,
LET'S SEE HOW THE ROLE OF IMFS TIES IN.
SO, WE'LL GO TO THE NEXT PAGE AND THERE WE GO,
MAKE THAT PRETTY. OKAY.
SO, THE WAY
THAT A SOLUTION FORMS IS WHEN THE INTERMOLECULAR FORCES
BETWEEN THE SOLUTE AND THE SOLVENT ARE COMPARABLE.
AND SO, THERE'S A COMMON SOLUBILITY RULE
THAT BASICALLY SAYS LIKE DISSOLVES LIKE.
AND THE PART THAT OFTEN GETS LEFT OUT
IS LIKE INTERMOLECULAR FORCES DISSOLVE
LIKE INTERMOLECULAR FORCES.
IT'S-- TO ME I THINK OF IT AS, LIKE,
SPEAKING THE SAME LANGUAGE.
SO, HIGHLY POLAR MOLECULE SPEAK A POLAR LANGUAGE
AND THEY LIKE TO INTERACT WITH OTHER POLAR MOLECULES.
AND NON-MOLAR--
POLAR MOLECULES, THEY HAVE THEIR OWN LANGUAGE AND SO,
THERE'S NOT AS MUCH AS TO SAY TO A POLAR MOLECULE.
WHEN WE TALK ABOUT SOLUBILITY,
MISCIBLE MEANS THAT THE TWO SUBSTANCES ARE SOLUBLE
AND THEY FORM A SOLUTION.
IMMISCIBLE MEANS INSOLUBLE, RIGHT?
AND THAT MEANS WE'RE GOING TO HAVE TWO OR MORE PHASES.
ALL RIGHTY.
SO, NOW, WE'VE LOOKED AT
THE VARIOUS COMPOUNDS THAT WE'VE BEEN STUDYING,
IONIC AND COVALENT COMPOUNDS,
AND LOOK AT THEIR ROLE
AS SOLUTES TO SEE WHAT HAPPENS CHEMICALLY.
SO, WE'LL START WITH IONS.
SO, HERE, WE HAVE A SALT CRYSTAL, OKAY?
SO, THIS SALT CRYSTAL,
THIS IS A SOLID, RIGHT, AND HERE,
WE-- THEY HAVE THE THREE-DIMENSIONAL ARRAY
OF THE CRYSTAL LATTICE.
AS SOON AS WE DISSOLVE THIS IN WATER,
WHAT QUITE LITERALLY HAPPENS IS THE WATER MOLECULES PULL APART
THE SODIUM AND THE CHLORIDE IONS
BECAUSE THEY CAN HAVE AN ATTRACTION BETWEEN.
SO, WE NOTICE THESE--
THIS DIAGRAM HERE, RIGHT,
THIS IS REPRESENTING WATER.
AND SO--
AND WE KNOW, RIGHT,
THAT THE HYDROGENS HAVE THOSE PARTIAL PLUSES
AND THE OXYGEN HAS THE PARTIAL MINUS.
SO, NOTICE HOW ALL OF THE WATER MOLECULES
ORIENT THEMSELVES TO CREATE AN ION DIPOLE,
AN H-BONDING INTERACTION BETWEEN THE WATER AND THE CHLORIDE.
AND THEN WE SEE OVER HERE IS THE SODIUM, RIGHT?
SO, THIS IS-- WE HAVE THE CHLORIDE IN THE CENTER,
THE CL-, RIGHT?
SO, THE WATERS ARE
GOING TO ORIENT THEMSELVES SO THAT ALL OF THOSE HYDROGEN IONS
WITH THEIR LARGE PARTIAL POSITIVES ARE ATTRACTED
AND THAT'S HOW THE WATER PULLS APART
THE SODIUM AND CHLORIDE IONS TO DISSOLVE THE SALT CRYSTAL.
NOW, THE WATER MOLECULES ARE GOING TO ORIENT
THEMSELVES IN THE OPPOSITE DIRECTION FOR THE SODIUM,
NOW, IT WILL BE THE PARTIAL MINUS
ON THE OXYGEN THAT'S GOING TO BE
ATTRACTED TO THE POSITIVE CHARGE OF THE SODIUM.
AND SO, THAT IS HOW IONS DISSOLVE TO BECOME SOLUTES
IN A SOLUTION.
SO, WE'VE SEEN IT AS A DIAGRAM BUT WE WANTED-- AND SO,
THAT HELPS US WITH OUR CONCEPTUAL UNDERSTANDING.
BUT THEN WE WANT TO BE ABLE TO DISTILL THIS DOWN
INTO LIKE A CHEMICAL REACTION, RIGHT?
SO, IF WE HAD OUR CALCIUM CHLORIDE SOLID, RIGHT, SO,
HERE'S OUR METAL AND OUR NON-METAL,
OUR CATION AND OUR ANIONS,
THIS IS OUR IONIC COMPOUND OFTEN CALLED SALTS.
SO, IF WE ADD THIS TO WATER, IT'S GOING TO DISSOCIATE.
SO, THE IMPORTANT THING
TO UNDERSTAND HERE IS WE HAVE A RATIO OF ONE CALCIUM ION,
RIGHT, TO TWO CHLORIDE IONS.
SO, WHEN WE WRITE THIS OUT,
WE WOULD SHOW HERE'S THE CALCIUM TWO PLUS
AND NOW IT'S GOING TO BE DISSOLVED IN WATER,
SO, AQUEOUS, AND THEN NOTICE THAT WHEN WE DO THE DISSOLUTION,
RIGHT, HERE, AS A SOLID,
ALL OF THE IONS ARE LOCKED TOGETHER IN THE CRYSTAL LATTICE.
BUT ONCE THEY'RE DISSOLVED,
THEY'RE INDEPENDENT, RIGHT?
THEY BECOME INDEPENDENT SOLUTES.
SO, EVEN THOUGH WHEN WE WRITE THE CHEMICAL FORMULA, WE SAY,
OKAY, FOR EVERY CALCIUM ION,
WE'RE GOING TO NEED TWO CHLORIDE IONS.
SO, THAT'S HOW WE WRITE THE CHEMICAL FORMULA.
BUT AS SOON AS THEY'RE DISSOLVED IN WATER,
THOSE TWO CHLORIDES IONS ARE COMPLETELY INDEPENDENT
OF EACH OTHER AND OF THE CALCIUM ION.
SO, IT'S IMPORTANT THAT YOU VISUALIZE THIS TRANSFORMATION
FROM SOLID TO AQUEOUS.
AND SO THEN, TO CHECK FOR YOUR UNDERSTANDING,
THERE'S ANOTHER EXAMPLE HERE.
AND IF WE LOOK AT THIS COMPOUND, THIS IS A GOOD OPPORTUNITY
TO HAVE A QUICK NOMENCLATURE CHECK IN.
IF WE LOOK AT THIS COMPOUND HERE,
AND I'M SURE EVERYONE CAN RECOGNIZE THIS AS IRON,
BUT WE REMEMBER THAT IRON HAS VARIABLE CHARGE.
SO, WHAT'S THE CHARGE ON THIS IRON ATOM?
TO FIGURE THAT OUT, RIGHT, WE LOOK AT THE ANION
AND WE SEE THAT WE HAVE NITRATE.
EACH NITRATE HAS A MINUS ONE CHARGE
AND WE HAVE THREE OF THEM, RIGHT?
SO, WE HAVE A ONE TWO TO THREE RATIO.
SO, THE IRON MUST BE +3.
SO, THIS COMPOUND HERE WOULD BE IRON
(III)
NITRATE. ALL RIGHT. OKAY.
NOW, BACK TO THE TASK AT HAND.
ALL RIGHTY. SO, WHEN WE TAKE THE IRON
(III)
NITRATE SOLID AND WE DISSOLVE IT IN WATER,
IT WILL RELEASE ONE, IRON
(III)
CATION AND THREE NITRATE IONS.
SO, IT'S IMPORTANT
WHEN WE'RE LOOKING AT THIS CHEMICAL FORMULA,
RIGHT, THAT WE KEEP--
WE UNDERSTAND WHAT THIS IS SAYING,
RIGHT, THAT THERE'S AN UNDERSTOOD ONE THERE, SO,
THERE'S OUR ONE TO THREE RATIO.
NITRATE HAS THE CHEMICAL FORMULA, NO3 WITH A -1 CHARGE.
WE NEVER BREAK APART THE POLYATOMIC IONS.
BUT IN THIS CASE, THERE ARE THREE POLYATOMIC IONS PRESENT.
AND SO, THAT BECOMES THE COEFFICIENT IN OUR REACTION.
SO-- LET'S SEE. YEAH.
SO, I THINK I WANT TO DO--
I'M GOING TO TALK ABOUT THE NEXT PAGE
AND THEN I'LL GIVE YOU A DEMONSTRATION.
BUT BRIEFLY HERE,
I WANT TO PUT OUT THAT THESE DISSOLVED IONS
WE OFTEN REFERRED TO THIS AS ELECTROLYTES.
AND THAT WILL HAVE MORE MEANING IN A MOMENT.
BUT I WANT TO TALK ABOUT MOLECULES
AS SOLUTES FIRST. OKAY.
SO, WE STILL ARE LOOKING AT SOLUTION FORMATION.
SO, IT'S STILL LIKE DISSOLVES LIKE. OKAY.
BUT REMEMBER, WITH MOLECULES, THE ATOMS ARE LOCKED TOGETHER,
ALL RIGHT, WITH COVALENT BONDS, ALL RIGHT?
SO, IT'S A VERY DIFFERENT SITUATION, SO, FOR EXAMPLE,
IF I HAVE HERE IS ETHANOL, OKAY?
ETHANOL IS A LIQUID BUT ANYONE THAT'S ENJOYED
A COCKTAIL HAS PERHAPS ADDED THEIR ETHANOL WITH SOME WATER
OR A CLUB SODA OR SOMETHING,
RIGHT, AND WE KNOW THAT THE ETHANOL
WILL DISSOLVE IN THE WATER. OKAY.
SO, THIS IS A VERY DIFFERENT, YOU KNOW,
A VERY DIFFERENT REACTION FROM WHAT WE'VE SAW FOR IONS.
WHAT HAPPENS HERE IS THERE'S THE CARBONS
AND THE OXYGEN, OKAY?
AND THEN, THIS DON'T REALLY MATTER OVER HERE
BUT I'LL PUT THEM IN.
OKAY. ALL RIGHT.
SO, THIS PART OF THE MOLECULE IS NON-POLAR.
WATER WANTS NOTHING TO DO WITH IT BUT THE WATER IS ATTRACTED
TO THIS HYDROXYL GROUP HERE AND SO,
BY NOW, YOU SHOULD BE SEEING THE PARTIAL CHARGES
WHENEVER YOU LOOK AT MOLECULES.
AND SO, THEN,
WE SEE THAT THERE'S STILL IS AN INTERACTION, RIGHT?
SO, THE WATER IS THE SOLVENT
AND THE ETHANOL IS THE SOLUTE.
AND SO, ETHANOL DISSOLVES IN WATER BECAUSE IT'S ABLE
TO H-BOND WITH THE WATER.
BUT NOTICE THAT THIS IS VERY DIFFERENT
FROM OUR PREVIOUS EXAMPLE.
THE ETHANOL MOLECULE STAYS INTACT.
SO, NOW, I WOULD LIKE TO SHOW YOU A LITTLE DEMO
TO EMPHASIZE THIS DIFFERENCE.
SO, HERE IS A SOLUTION THAT CONTAINS IONS
AND THEY'RE CALLED ELECTROLYTES
BECAUSE WE SEE THAT BECAUSE THE IONS ARE--
BE ABLE TO MOVE INDEPENDENTLY,
THEY CAN CARRY THE ELECTRICAL CHARGE.
AND THEN IF WE COMPARE THAT--
SO, HERE'S AN ETHANOL IN WATER AND NOW NOTICE,
RIGHT, THAT NOTHING'S LIGHTING UP
BECAUSE THERE ARE NO IONS PRESENT.
ALL OF THE ATOMS OF THE COVALENT COMPOUND,
MOLECULAR COMPOUND,
STAY LOCKED TOGETHER.
SO, MOLECULES, COVALENT COMPOUNDS,
THEY CAN DISSOLVE IN WATER
BUT THEY ARE NOT ABLE TO CARRY AN ELECTRICAL CURRENT,
WHERE IONIC COMPOUNDS,
THEY DISSOCIATE AND DISSOLVE INTO THEIR INDEPENDENT IONS
WHICH THEN MOVE FREELY AND CAN CARRY THE ELECTRICAL CURRENT
THAT WE SEE REPRESENTED HERE BY THE BRIGHT LIGHT.
OKAY. THE LAST TYPE OF SUBSTANCE
TO CONSIDER AS A SOLUTE WOULD BE THE GAS MOLECULES.
SO, MOLECULES IN THE GAS PHASE CAN ALSO DISSOLVE IN WATER.
AND THE INTERESTING THING HERE IS--
AND WE'VE TALKED-- IF YOU GO TO THE GAS LAW TUTORIAL,
WE'VE TALKED MORE ABOUT THIS,
BUT THE MAIN THING TO THINK ABOUT IS THAT GAS MOLECULES
CAN DISSOLVE IN WATER
AND AS WE INCREASE THE PRESSURE OF THE GAS,
WE INCREASE THE CONCENTRATION OF THE GAS, RIGHT?
SO, THAT MEANS CONCENTRATION, RIGHT, IN THE WATER.
AND THE INTERESTING THING ABOUT GASES THAT'S DIFFERENT
FROM SOLIDS IS REGARDING TEMPERATURE CHANGE.
SO, FOR SOLIDS,
AS WE INCREASE THE TEMPERATURE,
WE INCREASE THE SOLUBILITY IN WATER, RIGHT?
SO, IF A SOLID--
IF OUR SOLUTE IS A SOLID AND WE WANT IT TO DISSOLVE,
A LOT OF PEOPLE HAVE EXPERIENCED,
LIKE, IN THE WINTER,
IF YOU PUT SUGAR IN YOUR HOT TEA,
IT DISSOLVES REALLY QUICK,
AND THEN IN THE SUMMER,
IF YOU TRY TO PUT SUGAR INTO ICED TEA,
YOU GOT TO STIR AND STIR AND STIR
AND STIR TO GET IT TO DISSOLVE.
SO, FOR GAS, IT'S VERY INTERESTING
BECAUSE IT'S THE OPPOSITE.
HERE, AS WE DECREASE THE TEMPERATURE,
WE WILL INCREASE THE SOLUBILITY OF THE GAS IN WATER.
SO, THAT'S AN IMPORTANT DISTINCTION
TO MAKE BETWEEN SOLIDS AND GASES AS SOLUTES.
AND NOW, TO TIE THIS ALL TOGETHER,
LET'S APPLY THE CONCEPTS TO MAKE SURE
THAT YOU UNDERSTAND THEM SO YOU CAN DO YOUR HOMEWORK.
WHICH COMPOUND IS MORE SOLUBLE IN WATER?
WELL, IF WE LOOK HERE,
WE SEE WE HAVE A LARGE HYDROCARBON TAIL
AND THIS IS ALL NON-POLAR.
SO, THIS PART DOES NOT LIKE WATER, RIGHT?
BECAUSE WHEN WE-- IN MY DREAM WORLD, AS SOON AS YOU--
I SAY THE WORD WATER,
YOU CAN'T HELP IT, YOU THINK ABOUT WATER
AND ITS TETRAHEDRAL ELECTRON GEOMETRY
AND BENT MOLECULAR SHAPE,
AND ITS POLARITY,
AND SO, AS WE LOOK AT THIS FIRST MOLECULE HERE,
IT DOES HAVE THE ABILITY TO H-BOND WITH WATER
AND THEN IT HAS A BUNCH OF CARBONS THAT KEEP GOING.
ONE, TWO, THREE, FOUR, OKAY?
AND THEN THERE'S ALL THOSE HYDROGENS COMING OFF.
SO, THIS PART DOESN'T REALLY MATTER RIGHT NOW
BECAUSE WATER DOESN'T LIKE THIS PART, ALL RIGHT?
SO, WATER IS GOING TO COME IN AND BE ATTRACTED HERE, RIGHT?
THIS CAN H-BOND WITH WATER.
BUT THEN THIS PART, IT REALLY DOES MATTER, RIGHT?
THIS PART IS NON-POLAR, SO, IT REPELS THE WATER.
SO, NOW, IF WE LOOK AT THIS--
WE COMPARE IT TO THIS MOLECULE HERE,
WE SEE THAT WE STILL HAVE THE ABILITY
TO H-BOND WITH WATER,
AND HERE, WE HAVE A VERY SMALL NON-POLAR REGION
THAT REPELS THE WATER SO-- WELL,
BOTH MOLECULES HAVE A REGION
AND A MEAN GROUP THAT CAN H-BOND WITH WATER.
THE MOLECULE ON THE LEFT HAS A LARGE HYDROPHOBIC,
NON-POLAR REGION THAT'S GOING TO REPEL THE WATER.
SO, IT'S THE MOLECULE ON THE RIGHT
THAT WILL HAVE THE GREATER WATER SOLUBILITY
BECAUSE WHAT HAPPENS IS WHEN WE'RE LOOKING AT SOLUBILITY,
AS THE MOLECULES GET LARGER AND LARGER,
THEY CAN HAVE MIXED FEELINGS ABOUT WATER.
THE PART THAT CAN H-BOND WITH WATER IS ATTRACTED TO WATER,
BUT THE NON-POLAR PART REPELS THE WATER.
SO HERE, IF YOU CAN KIND OF THINK OF IT AS A VOTE,
THIS POLAR PART IS VOTING TO HANG OUT WITH THE WATER
AND NOW THERE'S ONE VOTE AGAINST.
SO, THE POLAR PART WINS.
BUT AS THE NONPOLAR PART GETS BIGGER AND BIGGER AND BIGGER,
THERE'S MORE VOTES AGAINST INTERACTING
WITH THE WATER WHICH LOWERS THE SOLUBILITY.
AND SO, NOW, LET'S DO ONE LAST PRACTICE HERE.
LET'S PREDICT WHETHER THE FOLLOWING COMPOUNDS ARE SOLUBLE
IN WATER OR OCTANE, OR BOTH.
SO, THE MAIN THING YOU NEED TO NOTICE ABOUT OCTANE,
RIGHT, IS IT'S A BIG NON-POLAR MOLECULE ALL HYDROCARBONS.
AND THEN, OF COURSE, WATER IS HIGHLY POLAR, RIGHT?
IT'S AN H-BONDER. OKAY.
WHERE NON-POLAR,
THAT'S GOING TO BE LONDON, OKAY?
SO, IF WE LOOK AT ETHANOL, WHICH WE USED AS OUR--
IN OUR DEMONSTRATION,
WE ALREADY KNOW THAT IT DISSOLVES IN WATER
BECAUSE IT CAN H-BOND BUT NOTICE,
IT ALSO HAS A BIG--
IT HAS SOME HYDROCARBONS HERE
THAT ARE NON-POLAR THAT WOULD LIKE THE OCTANE.
SO, ETHANOL CAN DISSOLVE IN WATER,
OCTANE OR BASICALLY WE COULD SAY BOTH.
THIS NEXT EXAMPLE WITH HEXANE,
WE HAVE A HYDROCARBON, NON-POLAR,
SO, IT'S GOING TO HATE WATER,
BUT IT'S GOING TO LOVE OCTANOL.
VEGETABLE OIL, THE CHEMICAL FORMULA
FOR VEGETABLE OIL IS VERY LARGE
AND COMPLEX BUT I THINK WE'VE ALL EXPERIENCED VEGETABLE OIL
IN THE FOODS THAT WE'VE EATEN AT SOME POINT.
AND SO, WHAT DO WE KNOW ABOUT IT?
DOES OIL--
IF YOU LOOK AT ITALIAN SALAD DRESSING,
WE KNOW THAT THE OIL AND THE WATER DON'T MIX.
SO, VEGETABLE OIL WILL NOT DISSOLVE IN WATER
BUT BECAUSE WE SEE THAT IT'S HYDROPHOBIC,
WE CAN DEDUCE THAT IT WOULD LIKE BEING WITH OCTANE
BECAUSE IT'S ALSO HYDROPHOBIC,
DOESN'T LIKE THE WATER, RIGHT?
HYDROPHOBIC, RIGHT?
WATER-FEARING. OKAY.
AND THEN, IF WE LOOK AT THIS LAST EXAMPLE, NOW,
WE HAVE OCTANOL.
SO, WE SEE THAT THERE IS THE POSSIBILITY
OF AN OH THERE, RIGHT?
SO, THIS PART DOES WANT AN H-BOND BUT NOW, IF WE LOOK,
RIGHT, THERE'S A HUGE NON-POLAR REGION.
SO, THIS--
SO, OCTANOL WILL NOT LIKE WATER.
IT WILL ONLY BE DISSOLVED IN OCTANE.
AND SO, THERE IS A RULE OF THUMB HERE,
WHEN WE HAVE SMALL MOLECULES,
TYPICALLY IT'S THE FOUR TO SIX CARBON RULE.
SO, IF WE HAVE H-BONDING IN A MOLECULE,
IT WILL CREATE WATER SOLUBILITY
IF THERE'S ONLY FOUR TO SIX CARBONS.
AS SOON AS THE CARBON CHAIN GETS GREATER
THAN FOUR TO SIX CARBONS,
THE NON-POLAR PART TAKES OVER
AND THE MOLECULE IS NO LONGER WATER SOLUBLE.
SO, THIS CONCLUDES THE OVERVIEW AND INTRODUCTION
TO HOW WE USE INTERMOLECULAR FORCES
TO UNDERSTAND AND PREDICT SOLUTION FORMATION.
SO, PLEASE TAKE SOME TIME NOW TO WORK A FEW PRACTICE PROBLEMS
TO REINFORCE YOUR UNDERSTANDING.