- WELCOME TO THE VIDEO TUTORIAL
THAT WILL GIVE US SOME EXTRA PRACTICE
ON PERCENT MASS/VOLUME CALCULATIONS.
SO IN PERCENT MASS/VOLUME IS ONE OF THE DIFFERENT WAYS
THAT WE COMMUNICATE SOLUTE CONCENTRATIONS.
SO THERE IS AN INTRODUCTORY VIDEO TUTORIAL
THAT GOES OVER SOLUTION CONCENTRATIONS,
THAT IT WOULD BE A GOOD IDEA
FOR YOU TO VIEW BEFORE VIEWING THIS TUTORIAL.
SO REMEMBER THAT PERCENT MASS OVER VOLUME WILL BE SYMBOLIZED %
(M/V),
BUT NOT EVERYBODY USES MASS.
SOME PEOPLE DESCRIBE IT AS WEIGHT.
AND SO DON'T BE CONFUSED BETWEEN THE MASS OR THE WEIGHT.
EITHER ONE IS THE--
SAME INFORMATION IS BEING COMMUNICATED.
NOW, IN USING PERCENT MASS OVER VOLUME, FOR EXAMPLE,
IF WE'RE TOLD THAT WE HAVE X%
(M/V),
THEN WHEN WE INTERPRET THIS, WE WILL--
THE X TELLS US THAT WE HAVE X GRAMS OF THE SOLUTE PER,
AND THEN THE VOLUME WILL BE IN MILLILITERS.
AND BECAUSE OF THE PERCENT, THAT MEANS,
WE WOULD HAVE ONE HUNDRED MILLILITERS.
SO THAT IS HOW WE READ THE CONCENTRATION UNITS.
SO LET'S PRACTICE CALCULATING PERCENT MASS/VOLUMES.
IF WE HAVE A HUNDRED MILLILITERS
OF A BLOOD SERUM CONTAINING FIVE MILLIGRAMS OF THYROXINE,
A HORMONE RELEASED BY THE THYROID GLAND.
WHAT IS THE CONCENTRATION IN PERCENT MASS OVER VOLUME?
SO HERE,
WHERE IT'S GOING TO CALCULATE THE PERCENT MASS/VOLUME.
SO THIS IS DONE IN A TRADITIONAL WAY WE CALCULATE PERCENTS.
THE MAIN THING HERE IS WATCHING THE UNITS.
WE NEED TO HAVE THE SOLUTE IN GRAMS,
THE VOLUME OF SOLUTION IN MILLILITERS,
AND THEN WE'RE GOING TO MULTIPLY BY A HUNDRED.
SO FOR THIS EXAMPLE,
THE MASS OF OUR SOLUTE IS FIVE MILLIGRAMS OF THE THYROXINE,
SO WE'LL JUST GIVE THAT A UPPERCASE T.
AND THEN WE HAVE A HUNDRED MILLILITERS OF SOLUTION.
AND SO WE'RE GOING TO NEED TO DO A UNIT CONVERSION HERE
BECAUSE THE MASS OF OUR SOLUTE IS IN MILLIGRAMS, NOT GRAMS.
WE DON'T HAVE TO DO ANYTHING WITH THE VOLUME
SINCE IT'S ALREADY IN MILLILITERS.
SO NOW, WE'LL DO A UNIT CONVERSION,
THAT THERE ARE A THOUSAND MILLIGRAMS IN ONE GRAM.
THERE'S ALSO A VIDEO TUTORIAL
THAT TALKS ABOUT UNIT CONVERSIONS.
SO IF THIS STEP IS CAUSING YOU SOME TROUBLE,
PLEASE TAKE ADVANTAGE OF THAT RESOURCE.
AND THEN BECAUSE IT'S GOING TO BE A PERCENT--
SO NOW WE HAVE OUR MASS IN GRAMS,
AND OUR VOLUME IN MILLILITERS,
AND THEN BECAUSE WE'RE DOING A PERCENT,
WE MULTIPLY BY A HUNDRED.
SO IF WE PUNCH THIS THROUGH OUR CALCULATOR, WE WOULD--
OOPS. OH, CRAP.
EXCUSE ME.
WE WOULD SEE THAT IT'S .005% THYROXINE.
AND THAT WOULD BE--
TO MAKE THAT, RIGHT,
SO THAT WOULD BE MASS OVER VOLUME OF THYROXINE.
SO THERE WOULD BE--
THERE WOULD BE OUR RESULT.
LET'S PRACTICE THAT ONE MORE TIME.
SO POTASSIUM IODIDE, WHEN WE HEAR THAT NAME,
WE INSTANTLY THINK OF THE CHEMICAL FORMULA.
IT IS USED TO TREAT IODINE DEFICIENCIES.
WHAT IS THE PERCENT WEIGHT OVER VOLUME,
REMEMBER THAT'S THE SAME AS MASS OVER VOLUME,
OF A 75 ML SOLUTION CONTAINING 2 GRAMS OF POTASSIUM IODIDE.
SO REMEMBER THAT WE WANT IT TO BE GRAMS/MILLILITERS X 100.
SO HERE'S OUR MASS, WE CAN TELL BY THE MASS UNITS OF GRAM,
2.0 GRAMS POTASSIUM IODIDE, 75 MILLILITERS OF THE SOLUTION,
AND BECAUSE WE'RE ASKED TO DO A PERCENT,
WE'LL MULTIPLY BY A HUNDRED,
AND THEN WE PUNCH THIS RESULT INTO OUR CALCULATOR
OR THESE VALUES.
AND WE WOULD SEE THAT IT WOULD BE--
OUR CALCULATOR TELLS US 2.6667% WEIGHT OVER VOLUME,
AND THEN FOUR SIG FIGS.
LET'S SEE HERE.
WE SHOULD HAVE TWO SIG FIGS, SO 2.7% WEIGHT OVER VOLUME.
AND NOW THAT I'VE MENTIONED SIG FIGS FOR THIS CALCULATION,
SOME OF YOU MAY NOT HAVE NOTICED UP
ABOVE THAT I IGNORED THE SIG FIGS HERE.
SO TWO SIG FIGS AND THREE SIG FIGS,
SO I MADE AN ERROR IN REPORTING THIS ANSWER.
I SHOULD HAVE ADDED A TRAILING ZERO,
SO THAT WE CORRECTLY REPORT IT TO TWO SIG FIGS,
OUR FINAL ANSWER. ALL RIGHTY.
NOW, SO CALCULATING THE PERCENT MASS/VOLUME
OF A SOLUTION IS AN IMPORTANT CALCULATION
THAT YOU WANT TO BE ABLE TO DO.
BUT SOMETIMES, WE'LL DO CALCULATIONS WHERE WE USE--
WE'RE GIVEN THE PERCENT MASS/VOLUME
AND WE HAVE TO USE IT AS A CONVERSION.
SO LET'S TRY THAT. OKAY.
SO HERE, WE HAVE EXAMPLES
WHERE WE'RE GIVEN THE PERCENT MASS/VOLUME
AND WE NEED TO USE THAT IN A CALCULATION.
FOR EXAMPLE, HOW MANY GRAMS OF SODIUM CHLORIDE, ALL RIGHT,
SO THIS IS WHAT WE'RE TRYING TO CALCULATE,
ARE NEEDED TO MAKE 750 MILLILITERS,
THERE'S A VOLUME OF,
HERE'S OUR CONCENTRATION, .95%
WEIGHT OVER VOLUME?
SO THE KEY HERE IS TO MAKE SURE
THAT WE UNDERSTAND HOW TO USE THIS CONCENTRATION INFORMATION.
SO THIS IS TELLING US THAT THERE'S .95
GRAMS OF OUR SOLUTE SODIUM CHLORIDE
IN EVERY HUNDRED MILLILITERS OF THE SOLUTION.
SO THIS WILL--
THIS IS THE KEY PIECE
THAT'S GOING TO HELP US SOLVE THIS QUESTION.
SO WE WANT 750 MLS OF THE SOLUTION.
SO THIS IS WHERE WE'RE GOING TO START.
WE'LL START HERE.
SO THIS IS THE SOLUTION WE WANT TO PREPARE.
AND THE CONCENTRATION THAT WE WANT TO PREPARE IS .95
GRAMS PER HUNDRED MLS.
SO WE LET THE UNITS GUIDE US.
WE HAVE MILLILITERS OF SOLUTION ON THE TOP.
SO WE'RE GOING TO USE THIS CONVERSION
DIRECTLY AS WE'VE WRITTEN IT.
KNOW THAT WE CAN ALWAYS FLIP THEM IF NEEDED.
ESPECIALLY WHEN WE'RE WORKING WITH CONCENTRATIONS, RIGHT,
IT'S AN IMPORTANT BRIDGE FROM SOLUTION TO SOLUTE.
SO NOT ONLY DO WE HAVE TO WRITE THE MAGNITUDE OF THE NUMBER,
IT'S UNITS, BUT WHAT EXACTLY ARE WE TALKING ABOUT.
AND THAT GIVES US THE ABILITY THEN TO CANCEL THIS.
SO NOW, WE'RE IN GRAMS OF SODIUM CHLORIDE, WE'RE DONE.
NOW, WE'LL TAKE THE TIME
TO PUNCH THE DATA INTO OUR CALCULATOR,
AND WE GET A FINAL RESULT.
WE WOULD NEED TO WEIGH OUT 7.125 GRAMS,
AND THEN OF COURSE,
WE'LL PAY ATTENTION TO SIG FIGS.
SO IN THIS EXAMPLE, WE HAVE TWO SIG FIGS HERE
BECAUSE THERE'S NO DECIMAL.
AND HERE, WE HAVE TWO SIG FIGS, AS WELL,
SO WE WOULD ROUND OUR ANSWER TO 7.1 GRAMS SODIUM CHLORIDE.
ALL RIGHTY.
LET'S TRY ONE MORE OF THIS TO HELP YOU FEEL COMFORTABLE
BEFORE YOU START WORKING ON YOUR HOMEWORK.
HOW MANY GRAMS OF GLUCOSE ARE NEEDED TO MAKE 500 MLS
OF A 5.5 PERCENT MASS OVER VOLUME SOLUTION.
SO FOR GLUCOSE,
WE'LL JUST GIVE IT THE UPPERCASE G, ALL RIGHT?
AND HOW MANY GRAMS--
SO IT'S VERY SIMILAR
TO THE PREVIOUS QUESTION, ALL RIGHT.
THIS IS THE VOLUME OF SOLUTION THAT WE WANT TO MAKE,
AND THEN HERE, ALL RIGHT,
SO TAKE THE TIME RIGHT NOW TO WRITE OUT
WHAT THIS CONCENTRATION IS TELLING US.
THIS IS THE KEY PIECE. RIGHT?
SO THIS CONCENTRATION IS TELLING US THAT WE HAVE 5.5 GRAMS
OF GLUCOSE IN EVERY 100 MILLILITERS OF SOLUTION, RIGHT?
SO I JUST WROTE IT DIFFERENTLY FROM UP ABOVE.
THESE ARE TWO WAYS TO WRITE THE SAME THING,
WHICHEVER WAY IS MORE COMFORTABLE FOR YOU.
ALL RIGHT?
I GUESS WE'LL JUST DO IT HERE FOR COMPLETION.
OKAY. SO THAT'S THE KEY,
THAT'S THE KEY PIECE.
NOW, WE CAN SOLVE THE PROBLEM.
WE WANT TO PREPARE 500 MILLILITERS
OF THE SOLUTION AND THE--
THIS CONCENTRATION VALUE IS WHAT ALLOWS US TO CONVERT
FROM THE SOLUTION TO THE SOLUTE,
THE GLUCOSE THAT WE'RE INTERESTED IN ADMINISTERING.
AND IN THIS CASE, WE'RE DONE, RIGHT?
WE HAVE THE MILLILITERS OF SOLUTION CANCELS
AND WE ARE LEFT WITH GRAMS OF GLUCOSE.
SO THE UNITS TELL US THAT WE'VE SET THE PROBLEM UP CORRECTLY,
SO NOW WE CAN TAKE THE TIME
TO ENTER THE DATA INTO OUR CALCULATOR.
AND WE FIND THAT WE WOULD NEED TO WEIGH OUT
27.5 GRAMS OF GLUCOSE.
AND IF WE LOOK AT OUR DATA, THERE IS A DECIMAL HERE,
SO THAT'S THREE SIG FIGS FOR THOSE TRAILING ZEROS.
HERE, WE'RE AT TWO SIG FIGS.
SO WE'LL REPORT OUR ANSWER TO TWO SIG FIGS
WITH THE FIVE WE ROUND UP.
SO WE WOULD NEED TO MEASURE OUT 28 GRAMS OF GLUCOSE.
ALL RIGHTY.
SO THERE'S A COUPLE PRACTICE PROBLEMS
TO HELP YOU FEEL MORE COMFORTABLE
WORKING WITH PERCENT MASS OVER VOLUME CONCENTRATION UNITS.
AND THIS WOULD BE A GOOD TIME TO WORK ON A FEW HOMEWORK QUESTIONS
TO REINFORCE YOUR UNDERSTANDING.