- WELCOME TO THE VIDEO TUTORIAL THAT WILL REVIEW MOLARITY
AND CALCULATIONS USING MOLARITY.
SO FOR INTRODUCTION TO SOLUTION CONCENTRATIONS,
PLEASE SEE THE INTRODUCTORY VIDEO.
BUT WE'LL JUMP RIGHT INTO MOLARITY.
SO MOLARITY IS REPRESENTED WITH AN UPPERCASE M
WHICH STANDS FOR MOLES OF SOLUTE OVER LITER OF SOLUTION.
SO FOR EXAMPLE IF WE HAVE A 0.28 MOLAR GLUCOSE SOLUTION,
WE CAN INTERPRET THIS INFORMATION ONE OF TWO WAYS.
WE CAN SEE IT AS 0.28 MOLES OF GLUCOSE
PER LITER OF SOLUTION
OR WE CAN WRITE IT OUT AS A CONVERSION FACTOR
0.28 MOLES GLUCOSE EQUALS ONE LITER SOLUTION.
SO AS WE'VE BEEN LEARNING,
CONCENTRATION UNITS ARE VERY IMPORTANT
BECAUSE THEY LINK THE SOLUTE TO THE SOLUTION.
SO THERE'S TWO MAJOR TYPES OF CALCULATIONS
THAT YOU'LL DO WITH MOLARITY.
AND THE FIRST ONE
IS TO JUST QUITE LITERALLY CALCULATE THE MOLARITY.
SO, FOLIC ACID IS AN ESSENTIAL VITAMIN
AND IS LINKED TO THE PREVENTION
OF NEURAL TUBE DEFECTS IN DEVELOPING EMBRYOS.
IF 236 MILLILITERS OF ORANGE JUICE,
ONE CUP OF ORANGE JUICE CONTAINS 75 MICROGRAMS OF FOLIC ACID,
WHAT IS THE CONCENTRATION IN MOLARITY?
SO THERE'S A LOT OF INFORMATION HERE.
WHENEVER WE'RE WORKING WITH MOLARITY,
IT'S VERY FREQUENT THAT WE'RE GOING TO NEED
TO CALCULATE THE MOLAR MASS OF THE SUBSTANCE.
SO REMEMBER TO CALCULATE THE MOLAR MASS,
WE SIMPLY ADD UP THE INDIVIDUAL ATOMIC MASSES USING THE RATIO
OF THE CHEMICAL FORMULA.
AND THEN HERE, I'D USED MICROGRAMS,
AND REMEMBER, IN CHEMISTRY WE'LL USE THE GREEK MICRO SYMBOL
BUT PROFESSIONALLY,
THE MICRO IS WITH MC.
ALL RIGHT.
SO NOW LET'S GET STARTED HERE.
SO THE FIRST THING WE'RE GOING TO NEED IS,
IF WE HAVE INFORMATION IN MICROGRAMS OR GRAMS
AND WE'RE ASKED TO GO TO MOLARITY,
WE'RE GOING TO NEED THE MOLAR MASS.
SO ALONG THE MARGINS OF OUR PAPER,
WE'RE GOING TO HAVE 19 CARBONS
AND THE PERIODIC TABLE GIVES US THE MOLAR MASS,
NINETEEN HYDROGENS, SEVEN NITROGENS,
AND SIX OXYGENS.
SO THE MOLAR MASS OF FOLIC ACID,
NOW THAT WE HAVE THAT SETUP,
WE CAN DO THE CALCULATION.
AND SO WE SEE THAT THE MOLAR MASS
OF FOLIC ACID IS 441.45 GRAMS PER MOLE.
SO THIS IS GOING TO BE A HELPFUL CONVERSION FACTOR
FOR US AS WE START OUR CALCULATION.
NOW, WE WANT TO KNOW MOLARITY.
SO WE WANT TO GET TO MOLES OF FOLIC ACID
PER LITER OF SOLUTION. OKAY.
IN THIS CASE, THE SOLUTION IS THE ORANGE JUICE.
SO WHY DO WE KNOW?
THE QUESTION GIVES US THE MASS OF FOLIC ACID.
SO WE HAVE 75 MICROGRAMS AND FOLIC ACID,
WE'LL JUST ABBREVIATE,
AND THAT 75 MICROGRAMS IS FOUND IN 236 MILLILITERS OF SOLUTION,
IN THIS CASE, ORANGE JUICE.
SO NOW IT'S A MATTER OF DOING CONVERSIONS.
WE NEED TO GET MICROGRAMS INTO MOLES
AND WE NEED TO GET MILLILITERS INTO LITERS.
SO SINCE OUR MOLAR MASS IS IN GRAMS PER MOLE
WE'LL DO A METRIC CONVERSION.
THERE ARE TEN TO THE SIX MICROGRAMS IN A GRAM.
NOW THAT WE ARE IN GRAMS WE CAN BRING IN OUR MOLAR MASS,
441.45 GRAMS IN EACH MOLE OF A FOLIC ACID.
AND SO NOW, THE FIRST PART IS DONE,
WE HAVE MOLES OF OUR SOLUTE FOLIC ACID.
WE CONVERTED OUT OF MICROGRAMS INTO GRAMS
AND USED THE MOLAR MASS TO GET FROM GRAMS TO MOLES.
SO WE'RE ALMOST THERE.
RIGHT NOW WE HAVE MOLES PER MILLILITER,
BUT WE RECOGNIZE THAT MOLARITY IS MOLES PER LITER.
SO WE BRING IN ONE MORE UNIT CONVERSION
THERE THEN WE'RE GOING TO GET FROM MILLILITERS TO LITERS.
SO WE CANCEL THAT MILLILITERS SO NOW WE HAVE MOLES OF SOLUTE
AND LITER OF SOLUTION.
NOW WE--
THAT OUR UNITS TELL US WE'RE DONE,
WE'VE DONE EVERYTHING WE NEEDED TO DO,
WE CAN GO AHEAD AND PUNCH THESE VALUES
INTO OUR CALCULATOR TO GET THE FINAL RESULT.
WOW. SO VERY-- RIGHT.
SO 7.199 X 10 TO THE
-7 MOLAR, NOT VERY MUCH FOLIC ACID.
BUT NOW, THE LAST THING
WE WANT TO DO IS WE WANT TO CHECK OUR SIG FIGS
SO WE CAN REPORT THE ANSWER TO THE CORRECT SIG FIGS.
SO WE SEE HERE WITH THE 75 MICROGRAMS,
WE HAVE TWO SIG FIGS, THREE SIG FIGS.
HERE WE HAVE INFINITE BECAUSE IT'S DEFINED,
HERE WE HAVE FIVE SIG FIGS, AND HERE WE HAVE INFINITE.
SO OUR FINAL ANSWER WE WANT TO REPORT TO TWO SIG FIGS,
SO THAT WOULD BE 7.2 X 10 TO THE
-7 MOLAR FOLIC ACID.
SO IT'S AMAZING
THAT SUCH A SMALL CONCENTRATION CAN MAKE A BIG--
SUCH A BIG AFFECT IN THE HEALTH OF DEVELOPING EMBRYOS.
NOW LET'S GO TO THE NEXT PRACTICE PROBLEM.
SO HERE WE HAVE ASCORBIC ACID ALSO KNOWN AS VITAMIN C,
AN IT'S A POWERFUL ANTIOXIDANT
WITH THE MOLECULAR FORMULA C6H8O6.
IT HELPS THE BODY FORM
AND MAINTAIN CONNECTIVE TISSUE INCLUDING BONES,
BLOOD VESSELS AND SKIN.
SO IF THAT SAME CUP OF ORANGE JUICE CONTAINS A HUNDRED
AND TWENTY MILLIGRAMS OF VITAMIN C,
WHAT IS THE CONCENTRATION IN MOLARITY? RIGHT.
SO AS SOON AS WE SEE MOLARITY
WE THINK MOLES PER LITER AND WE HAVE GRAM--
MILLIGRAMS OF OUR VITAMIN C. SO ONCE AGAIN THE MARGINS
OF OUR PAPER START TO GET FILL.
THERE ARE SIX CARBON ATOMS, THEY, EACH WAY,
12.01 GRAMS PER MOLE,
EIGHT HYDROGENS,
AND SIX OXYGENS.
SO WE CAN PUNCH THESE VALUES INTO OUR CALCULATOR.
AND WE FIND OUT THAT THE MOLAR MASS
OF ASCORBIC ACID IS A 176.14 GRAMS PER MOLE.
ALL RIGHTY.
SO THIS QUESTION IS VERY SIMILAR TO THE PREVIOUS ONE.
WE WERE GIVEN A SPECIFIC MASS OF VITAMIN C,
120 MILLIGRAMS VITAMIN C.
AND OUR SOLUTION IS THE ORANGE JUICE 236 MILLILITERS.
SO THIS TIME THAT WE WERE GIVEN OUR MASS IN MILLIGRAMS,
SO WE'LL USE THE MILLIGRAM TO GRAM METRIC CONVERSION,
AND THEN WE USE THE MOLAR MASS
OF VITAMIN C TO GET TO MOLES OF VITAMIN C,
AND THEN LAST BUT NOT THE LEAST,
MOLARITY IS DEFINED AS MOLES PER LITER,
AND AT THIS POINT MILLIGRAMS HAVE CANCELLED,
AND GRAMS HAVE CANCELLED,
WE HAVE MOLES PER MILLILITER.
SO WE NEED ONE LAST UNIT CONVERSION.
THERE ARE A THOUSAND MILLILITERS IN A LITER.
SO NOW WE GET RID OF THOSE MILLILITERS
AND WE'RE LEFT WITH MOLES OF SOLUTE PER LITER OF SOLUTION.
SO THE UNITS TELL US THAT WE'VE PERFORMED ALL
THE NECESSARY CONVERSIONS SO NOW
WE CAN GO AHEAD AND PUNCH THESE VALUES
INTO OUR CALCULATOR TO GET OUR FINAL RESULT.
AND SO MY CALCULATOR IS GIVING ME--
LET'S SEE. RIGHT.
0.00289 MOLARITY OF VITAMIN C.
AND THEN ONCE WE FINISH THE CALCULATION,
TAKE A MOMENT TO LOOK BACK AT THE SIG FIGS AND ONCE AGAIN,
RIGHT, THERE IS NO DECIMAL THERE.
SO TWO SIG FIGS, THREE SIG FIGS,
INFINITE, INFINITE, RIGHT,
THESE ARE INFINITE BECAUSE THEY'RE DEFINED
BY THE METRIC SYSTEM.
AND OUR MOLAR MASS HAS FIVE SIG FIGS, SO OUR FINAL RESULT
SHOULD BE REPORTED TO TWO SIGNIFICANT FIGURES.
SO THAT WOULD--
THEN REMEMBER LEADING ZEROS NEVER COUNT,
SO THAT WOULD BE 0.0029 MOLAR VITAMIN C. ALL RIGHTY.
SO MOLARITY IS MOLES PER LITER AND YOU WANT TO BE ABLE--
IF YOU'RE GIVEN THE MASS OF THE SOLUTE
AND A VOLUME OF SOLUTION,
YOU WANT TO BE ABLE TO CALCULATE THE MOLARITY,
RECOGNIZING THAT YOU'RE MOST LIKELY
HAVE TO CALCULATE THE MOLAR MASS.
BUT SOMETIMES, WE'RE GOING TO DO CALCULATIONS
WHERE MOLARITY IS GOING TO BE A CONVERSION FACTOR.
SO LET'S PRACTICE SOME OF THOSE.
ALL RIGHT.
SO HERE, THE MOLARITY IS GIVEN TO US IN THE QUESTION
AND WE'RE GOING TO USE IT TO HELP CALCULATE THE FINAL ANSWER.
SO IF A .28 MOLAR GLUCOSE SOLUTION IS ISOTONIC
WITH RED BLOOD CELLS,
THEN HOW MANY GRAMS
OF GLUCOSE ARE NEEDED TO PREPARE 500 MILLILITERS OF THE SOLUTION?
SO THIS IS THE KEY PART HERE, IS WHEN WE GET THE MOLARITY
WE NEED TO RECOGNIZE WHAT THIS IS TELLING US.
THIS IS TELLING US THAT WE HAVE 0.28 MOLES OF GLUCOSE
IN EVERY LITER OF SOLUTION.
ALL RIGHTY.
SO WHAT'S THE QUESTION ASKING?
SO THE QUESTION'S ASKING US,
HOW MANY GRAMS OF GLUCOSE DO WE NEED
IF WE WANT TO PREPARE THE 500 MILLILITER SOLUTION?
SO WE START WITH THE VOLUME
OF THE SOLUTION WE'RE TRYING TO PREPARE.
SO WE BEGIN HERE, 500 MILLILITERS OF OUR SOLUTION.
AND NOW MOLARITY IS GOING TO BE THE BRIDGE
FROM THE SOLUTION TO THE SOLUTE
BECAUSE WE'VE BEEN ASKED TO DETERMINE HOW MANY GRAMS
OF SOLUTE WE NEED TO ADD TO THIS 500 ML.
SO WE HAVE A UNIT DISCONNECT HERE.
WE HAVE MILLILITERS AND LITERS.
SO IF YOU CAN DO THIS IN YOUR HEAD THAT'S AWESOME.
OTHERWISE JUST GO AHEAD, RIGHT,
AND THERE'S A THOUSAND MILLILITERS AND A LITER.
NOW WE'VE GOTTEN RID OF THE MILLILITERS
AND WE'RE IN LITERS.
NOW WE CAN BRING MOLARITY.
MOLARITY TELLS US THAT FOR EVERY LITER OF SOLUTION
WE NEED 0.28 MOLES OF GLUCOSE.
ALL RIGHTY.
NOW COMES THE LAST LITTLE BIT,
WE NEED TO GO FROM MOLES OF GLUCOSE TO GRAMS OF GLUCOSE.
SO THIS IS WHERE WE NEED TO BRING IN THE MOLAR MASS.
SO ALONG THE MARGINS OF OUR PAPER,
LOOKING AT THE CHEMICAL FORMULA OF GLUCOSE,
THERE ARE SIX CARBONS THAT EACH WAY 12.01 GRAMS PER MOLE,
12 HYDROGENS, AT ABOUT ONE GRAM PER MOLE EACH,
AND SIX OXYGENS.
SO WE ADD UP ALL OF THOSE VALUES AND WE GET THE MOLAR MASS
OF GLUCOSE AS 180.18 GRAMS PER MOLE.
ALL RIGHTY.
SO NOW WE CAN PLUG IN THE MOLAR MASS,
EVERY MOLE OF GLUCOSE WEIGHS A 100.18 GRAMS.
SO LET'S CHECK OUR UNITS.
WE GOT RID OF LITERS AND WE GOT RID OF MOLES
AND SO WE'RE LEFT WITH GRAMS OF GLUCOSE WHICH IS EXACTLY
WHAT THE QUESTION IS ASKING FOR.
SO SINCE OUR UNITS ARE USING
THAT THE CALCULATION IS COMPLETE,
WE'LL GO AHEAD AND PUNCH THESE NUMBERS
INTO OUR CALCULATOR
AND THE CALCULATOR SPITS OUT 25.225 GRAMS OF GLUCOSE,
SO THEN OUR LAST STEP IS TO REPORT THE CORRECT SIG FIGS.
SO HERE, WE HAVE A DECIMAL ON THIS VOLUME.
SO THIS TRAILING ZEROS COUNT,
METRIC UNIT CONVERSION DEFINED,
THE CONCENTRATION OF GLUCOSE ONLY TWO SIG FIGS,
AND THE MOLAR MASS FIVE.
SO THE WORST DATA LIMITS ARE RESULT,
SO WE WOULD ONLY NEED TO WEIGH OUT
25 GRAMS OF GLUCOSE TO PREPARE THE SOLUTION.
ALL RIGHT.
ONE LAST PRACTICE USING MOLARITY AS A--
IN CALCULATIONS. OKAY.
IN THIS QUESTION WE HAVE--
THERE ARE THREE GRAMS OF VITAMIN C AVAILABLE
TO PREPARE 0.0852 MOLAR SOLUTION.
TO WHAT VOLUME IS THE VITAMIN C DILUTED?
ALL RIGHT. SO THIS ONE IS A SLIGHTLY DIFFERENT QUESTION.
LET'S FOCUS ON MOLARITY.
ALL RIGHT.
SO THIS IS THE CONCENTRATION WE WANT TO PREPARE SO WHEN WE SEE
THIS WE RECOGNIZE THAT IT'S TELLING US 0.0852 MOLES
OF VITAMIN C PER ONE LITER OF SOLUTION, RIGHT.
SO THAT'S WHAT THAT'S TELLING US.
SO THIS IS--
THIS CONCENTRATION WILL BE THE CONVERSATION
THAT GETS US FROM OUR SOLUTE TO OUR SOLUTION.
NOW, IN THIS EXAMPLE, WE'RE STARTING WITH THE SOLUTE.
WE'VE GONE TO THE SHELF AND ALL WE CAN FIND ARE THREE GRAMS
OF VITAMIN C. SO WE NEED TO GET TO MOLES.
ON THE PREVIOUS PAGE,
WE ALREADY DETERMINED THAT VITAMIN C HAS A MOLAR MASS
OF A 176.14 GRAMS PER MOLE.
SO WE'RE GOING TO--
WHENEVER WE HAVE GRAMS AND MOLES IN THE SAME CALCULATION,
THAT SHOULD BE A FLAG FOR MOLAR MASS.
SO WE BRING IN THE MOLAR MASS.
NOTICE THIS TIME WE'RE USING IT UPSIDE DOWN,
AND THAT'S FINE BECAUSE WE CAN FLIP THEM ANYWAY WE WANT.
SO WE'VE USES THE MOLAR MASS
TO GET THE GRAMS OF VITAMIN C INTO MOLES OF VITAMIN C.
AND NOW WE CAN USE THE MOLARITY CONCENTRATION TO CONVERT.
NOW WE'RE CONVERTING FROM THE SOLUTE TO THE SOLUTION.
SO FOR EVERY 0.0852 MOLES OF VITAMIN C,
WE WILL HAVE ONE LITER OF SOLUTION.
SO NOW IF WE LOOK HERE,
WE STARTED WITH GRAMS OF VITAMIN C,
WE CANCELLED-- WE CONVERTED THOSE TO MOLES,
CANCELLING OUT THE GRAMS,
AND THEN USING OUR CONCENTRATION,
WE CANCEL THE MOLES OF VITAMIN C,
AND NOW WE HAVE THE VOLUME OF SOLUTION.
AND SINCE THE QUESTION DIDN'T SPECIFY VOLUME UNITS,
LITERS ARE A PERFECTLY GOOD VOLUME UNIT.
SO WE CAN STOP THERE SO THAT WE'LL GO AHEAD
AND PLUG THESE VALUES INTO OUR CALCULATOR.
AND WE SEE THAT WE COULD PREPARE .1999
LITERS OF SOLUTION.
SO WE'LL GO BACK AND LOOK AT OUR SIG FIGS.
TWO SIG FIGS HERE,
WE COUNT THE ZERO BECAUSE OF THE DECIMAL,
FIVE SIG FIGS, AND RIGHT HERE LEADING ZEROS NEVER COUNT,
THREE SIG FIGS, SO WE'RE LEFT WITH TWO.
SO THIS WOULD ROUND TO 0.20 LITERS OF SOLUTION, RIGHT?
OR 200 MILLILITERS, WE HAVE TO PUT THE OVERBAR.
ALL RIGHT.
SO WE WOULD TAKE THESE--
THE THREE GRAMS OF VITAMIN C AND WE WOULD ADD 200 MILLILITERS
OF WATER TO CREATE THE DESIRED CONCENTRATION.
SO THIS CONCLUDES OUR PRACTICE WITH MOLARITY.
NOW WOULD BE A GREAT TIME
TO WORK ON SEVERAL HOMEWORK QUESTIONS RELATED TO MOLARITY
TO REINFORCE YOUR UNDERSTANDING.