- WELCOME TO A VIDEO TUTORIAL THAT EXPLAINS THE CONCEPT
OF EQUIVALENTS PER LITER AS A CONCENTRATION UNIT.
THERE IS AN INTRODUCTORY VIDEO TUTORIAL
THAT GIVES AN OVERVIEW OF SOLUTION CONCENTRATIONS,
IT'S A GOOD IDEA TO WATCH THAT VIDEO FIRST.
LET'S BEGIN.
SO EQUIVALENTS ARE USED WHEN WE'RE KEEPING TRACK
OF THE CHARGE IN A SOLUTION.
SO EQUIVALENTS ONLY APPLY TO IONIC COMPOUNDS,
ALSO REFERRED TO AS SALTS.
NOW EQUIVALENTS ARE RELATED THE MOLE AND THE MOLAR MASS,
AND THEN WE HAVE TO BRING IN CHARGE.
SO THE NUMBER OF EQUIVALENTS IS THE CHARGE OF THE ION PER MOLE.
AND THEN THE GRAMS, THAT'S SIMPLY THE MOLAR MASS.
ALL RIGHT. SO FOR EXAMPLE,
IF WE HAD CA2+, RIGHT, ONE MOLE OF CA2+,
BECAUSE OF THE POSITIVE TWO CHARGE
WOULD EQUAL TWO EQUIVALENTS.
AND THEN WE WOULD LOOK TO THE PERIODIC TABLE
AND WE WOULD SEE THAT THAT WOULD BE A MASS OF 40.08 GRAMS.
SO FOR EACH ION, WE CAN RELATE THE NUMBER OF MOLES
TO THE EQUIVALENTS THROUGH THE CHARGE,
AND THEN WE CAN RELATE THAT TO THE MASS OF THAT PARTICULAR ION.
NOW, THE CONCENTRATION OF ELECTROLYTES,
IONS AND BODILY FLUIDS, IS VERY LOW,
SO WE TEND TO USE A SMALLER MILLI UNIT.
SO LET'S GO THROUGH THE CONVERSION
FROM MOLES, AND, EQUIVALENTS,
AND GRAMS TO MILLIMOLES,
MILLIEQUIVALENTS, AND MILLIGRAMS.
SO IF WE HAD ONE MOLE,
THAT WOULD BE THE SAME AS SAYING WE HAD A THOUSAND MILLIMOLES,
AND THAT WOULD
THE SAME AS SAYING WE HAVE A THOUSAND MILLIEQUIVALENTS,
AND THE SAME THING AS SAYING WE HAVE A THOUSAND MILLIGRAMS.
SO THEN WHAT WE CAN DO IS WE CAN JUST DIVIDE
EACH OF THESE BY THE COMMON FACTOR OF A THOUSAND,
AND SO THIS EQUALITY REDUCES TO ONE MILLIMOLE
OF A SUBSTANCE EQUALS THE NUMBER OF CHARGES FOR MILLIEQUIVALENTS,
OR MILLIGRAMS.
SO LET'S DO AN EXAMPLE FOR ALUMINUM HERE.
SO WE CAN SAY IF WE HAVE ONE MILLIMOLE OF ALUMINUM,
BECAUSE OF THE POSITIVE THREE CHARGE,
THAT WOULD BE THREE MILLIEQUIVALENTS.
AND THEN IF WE GO TO THE PERIODIC TABLE NOW,
WE WOULD SEE THIS-- INSTEAD OF GRAMS,
WE WOULD SEE THIS AS MILLIGRAMS,
THE MOLAR MASS OF ALUMINUM.
AND SO WE CAN DO THIS FOR ANY ION.
ALL RIGHTY.
SO HERE'S A TABLE THAT PROVIDES, I THINK, A GOOD SUMMARY
OF THE RELATIONSHIP BETWEEN EQUIVALENTS,
MOLES, AND GRAMS.
SO I THINK I MIGHT TRY TO ZOOM IN A LITTLE BIT RIGHT HERE.
OKAY. THERE WE GO.
ALL RIGHT. SO HERE,
WE HAVE THE MOLAR MASS, FOR EXAMPLE,
OF SODIUM WITH THE PLUS ONE CHARGE,
ONE EQUIVALENT EQUALS ONE MOLE, RIGHT?
AND 1 MOLE EQUALS THE 22.9 GRAMS.
SO HERE, WE HAVE ONE EQUIVALENT
THEN IS SIMPLY EQUAL TO THE MOLAR MASS.
WHERE THINGS CHANGE IS WHEN WE HAVE,
RIGHT, WITH MAGNESIUM,
THERE ARE TWO EQUIVALENTS PER MOLE.
SO THE MASS OF MAGNESIUM
TO CREATE A PLUS 1 CHARGE IS ONLY 12.15 GRAMS.
AND THEN WE CAN CONTINUE GOING,
WE'LL DO ONE MORE EXAMPLE HERE.
LET ME-- WE SHOULD TRY AN ANION, RIGHT?
IF WE HAD PHOSPHATE,
THE MOLAR MASS OF PHOSPHATE IS WRITTEN HERE.
ONE MOLE OF PHOSPHATE IS EQUAL
TO THREE EQUIVALENTS BECAUSE OF THE MINUS THREE CHARGE, RIGHT?
AND THE MOLAR MASS IS HERE,
SO WE WOULD TAKE THE MOLAR MASS AND WE WOULD DIVIDE BY THREE,
AND THIS GIVES US THE MASS THAT'S A PHOSPHATE,
EQUIVALENT TO--
THAT CREATES ON EQUIVALENT OF CHARGE.
SO WHEN YOU THINK ABOUT ONE EQUIVALENT, YOU THINK ABOUT--
THAT'S ONE UNIT OF CHARGE,
AND IT CAN BE POSITIVE OR NEGATIVE.
ALL RIGHTY.
NOW, LET'S GO TO THE NEXT PAGE AND PRACTICE DOING
SOME CALCULATIONS WITH EQUIVALENTS.
ALL RIGHTY.
SO FOR ME, ANYTIME I SEE EQUIVALENTS IN THERE,
I'M GOING TO REMIND MYSELF THAT--
OH, THAT SHOULD BE TWO PLUS. RIGHT.
SO-- AND I SEE MILLIS HERE,
SO WE'LL GO AHEAD AND WORK IN MILLI.
SO REMEMBER THAT ONE MILLIMOLE OF CALCIUM WITH THE PLUS
TWO CHARGE IS GOING TO BE TWO MILLIEQUIVALENTS,
AND THEN WE LOOK TO THE PERIODIC TABLE,
AND THAT WOULD BE 40.08 MILLIGRAMS.
ALL RIGHT.
SO ANYTIME WE SEE MILLIEQUIVALENTS,
WE WANT TO LOOK AT THE ION IN QUESTION
AND PROBABLY REMIND OURSELVES OF THIS RELATIONSHIP.
NOW, LET'S LOOK MORE CLOSELY AT THE QUESTION ITSELF.
BLOOD PLASMA TYPICALLY CONTAINS FIVE MILLIEQUIVALENTS
PER LITER OF CALCIUM IONS.
CALCULATE HOW MANY MILLIGRAMS
OF CALCIUM ARE IN 250 MILLILITERS OF THE BLOOD PLASMA.
ALL RIGHT.
SO THE OTHER PIECE OF INFORMATION
WE HAVE IS RIGHT HERE,
THAT WE HAVE FIVE MILLIEQUIVALENTS
PER LITER OF BLOOD, ALL RIGHT?
SO THIS INFORMATION CAME FROM THE QUESTION,
AND THIS TOP INFORMATION CAME FROM OUR UNDERSTANDING
OF EQUIVALENTS.
NOW WE CAN SOLVE THE PROBLEM.
ALL RIGHT.
WE HAVE 250 MILLILITERS OF BLOOD,
AND SO LET'S SEE HERE.
OH, SO WE HAVE MILLILITERS AND WE HAVE LITERS HERE,
SO WE GOT A UNIT DISCONNECT.
SO THERE'S 10 TO THE 3RD MILLILITERS IN A LITER,
AND NOW WE CAN GET FROM THE BLOOD TO THE CALCIUM.
SO FOR EVERY LITER OF BLOOD,
THERE ARE 5.0 MILLIEQUIVALENTS OF CA2+.
AND NOW, THE QUESTION'S ASKING US HOW MANY MILLIGRAMS OF CA2+?
SO WE HAVE MILLIEQUIVALENTS,
SO NOW WE BRING IN OUR UNDERSTANDING
THAT FOR EVERY 2 MILLIEQUIVALENTS OF CALCIUM,
THAT WOULD BE--
CORRESPOND TO A MASS OF 40.08 MILLIGRAMS
OF CALCIUM. ALL RIGHT.
LET'S CHECK OUR UNITS, I THINK WE'RE DONE.
SO INITIALLY, WE STARTED IN MILLILITERS OF BLOOD,
AND WE HAD TO DO A QUICK UNIT CONVERSION TO GET TO LITERS.
ONCE WE WERE IN LITERS OF BLOOD,
WE COULD USE THE EQUIVALENTS OF CALCIUM AND BLOOD.
AND SO THEN WE ENDED UP WITH MILLIEQUIVALENTS OF CALCIUM
AND THEN WE USE OUR UNDERSTANDING OF CALCIUM
AND EQUIVALENTS TO GO FROM MILLIEQUIVALENTS TO MILLIGRAMS.
SO NOW WE'RE LEFT WITH MILLIGRAMS OF CALCIUM,
WHICH IS EXACTLY WHAT THE QUESTION ASKED FOR.
SO OUR SETUP IS COMPLETE,
WE PUNCH THE VALUES INTO OUR CALCULATOR,
AND WE GET A FINAL RESULT OF 25.05 MILLIGRAMS OF CA2+.
AND THEN LAST BUT NOT LEAST, WE SCAN, WE LOOK AT OUR DATA.
TWO SIG FIGS HERE, NO DECIMAL,
INFINITE SIG FIGS, TWO AND FOUR SIG FIGS.
SO WE WANT TO REPORT OUR ANSWER TO TWO SIG FIGS.
SO THEY WOULD BE 25 MILLIGRAMS OF CA2+.
ALL RIGHTY.
LET'S TRY ONE MORE PRACTICE CALCULATION
BEFORE YOU GET STARTED ON YOUR HOMEWORK.
HOW MANY MILLIEQUIVALENTS OF BICARBONATE ARE PRESENT
IN 75 MILLILITERS OF BLOOD SERUM SAMPLE WITH A CONCENTRATION
OF 25 MILLIEQUIVALENTS PER LITER OF BICARBONATE?
ALL RIGHTY.
SO IF WE HAVE, LET'S SAY, AGAIN,
WE HAVE MILLIEQUIVALENTS,
SO WE WILL GO ONE MILLIMOLE,
SO WE HAVE ONE MILLIMOLE OF BICARBONATE.
AND THAT WILL EQUAL ONE MILLIEQUIVALENT OF CHARGE
BECAUSE THERE'S ONLY A CHARGE THERE.
AND NOW WE NEED THE MOLAR MASS.
SO FOR THE MOLAR MASS,
THERE'S ONE HYDROGEN, ONE CARBON,
AND THREE OXYGENS.
SO WE ADD UP ALL OF THE MOLAR MASSES USING THE RATIOS
FROM THE FORMULA SUBSCRIPTS
AND WE SEE THAT FOR SODIUM BICARBONATE--
OR EXCUSE ME,
JUST FOR BICARBONATE,
THE MASS IS 61.02 GRAMS PER MOLE.
SO 61.02, RIGHT?
SO GRAMS PER MOLE,
OR 61.02 MILLIGRAMS PER MILLIMOLE.
ALL RIGHT. OKAY.
SO THIS IS WHAT WE BRING TO THE TABLE
AS STUDENTS OF CHEMISTRY.
THE QUESTION LETS US KNOW THAT THERE'S 25 MILLIEQUIVALENTS
OF BICARBONATE IN EVERY LITER OF BLOOD.
SO THAT COMES FROM THE QUESTION.
AND NOW, RIGHT, WE WANT TO KNOW HOW MANY MILLIEQUIVALENTS,
THAT'S WHAT WE'RE TRYING TO CALCULATE,
THE MILLIEQUIVALENTS OF BICARBONATE.
AND SO WHERE DO WE START?
THE ONLY THING LEFT, RIGHT?
WE HAVE A 75 MILLILITER BLOOD SAMPLE.
OKAY. SO ONCE AGAIN,
WE HAVE THAT UNIT DISCONNECT THAT OUR SAMPLE'S IN MILLITERS,
BUT THE INFORMATION IN THE QUESTION'S IN LITER.
SO WE BRING IN OUR UNIT CONVERSION.
AND NOW THAT WE'RE IN LITERS,
WE CAN USE THE EQUIVALENT CONCENTRATION OF BICARBONATE,
25 MILLIEQUIVALENTS.
WOW, SEE, AND IN THIS CASE, WE DIDN'T EVEN NEED THIS PART,
BUT I TEND TO JUST DO IT ANYWAY.
SO IT'S GOOD REVIEW.
LET'S DOUBLE CHECK OUR UNITS,
MILLILITERS OF BLOOD CANCEL, LITERS OF BLOOD CANCEL,
AND WE'RE LEFT WITH MILLIEQUIVALENTS OF BICARBONATE,
WHICH IS WHAT THE QUESTION ASKED FOR.
SO WE'RE READY TO PERFORM THE CALCULATION.
AND WE FIND OUT THAT WE WOULD HAVE 1.875 MILLIEQUIVALENTS
OF BICARBONATE,
AND THAT'S 75 MILLILITERS OF BLOOD.
AND THEN LAST BUT NOT LEAST, WE LOOK BACK AT OUR DATA,
AND WE HAVE THREE SIG FIGS HERE, INFINITE--
OKAY, BECAUSE IT'S DEFINED, AND TWO SIG FIGS.
SO ONCE AGAIN, WE'RE ROUNDING TO TWO SIG FIGS.
SO THERE ARE 1.9 MILLIEQUIVALENTS
OF BICARBONATE IN THE 75 MILLILITER BLOOD SAMPLE.
WELL, THIS CONCLUDES THE EQUIVALENTS TUTORIAL,
AND NOW WOULD BE A GOOD TIME TO WORK A FEW PRACTICE PROBLEMS
TO REINFORCE YOUR UNDERSTANDING.