SOLUTIONS & CONCENTRATIONS
• WHAT IS A SOLUTION ?
• WHAT IS CONCENTRATION & HOW IS
IT MEASURED ?
IS DISSOLVING A CHEMICAL OF A PHYSICAL
PROCESS ?
• IF SUGAR IS DISSOLVED IN WATER IS ITS CHEMICAL
NATURE CHANGED ?
• NO !!
• IF THE SOLUTION IS DRIED, A WHITE, SWEET
CRYSTALLINE SUBSTANCE (SUGAR) IS OBSERVED.
• THEREFORE DISSOLVING IS A PHYSICAL CHANGE. THE
CHEMICAL PROPERTIES OF A SUBSTANCE MUST BE
CHANGED IN ORDER FOR A CHEMICAL CHANGE TO
OCCUR !
A SOLUTION THEN IS THE RESULT OF THE
PHYSICAL CHANGE CALLED DISSOLVING, BUT
PRECISELY, WHAT IS A SOLUTION?
• THE OPPPOSITE OF A SOLUTION IS A SUSPENSION.
• MUDDY WATER IS A SUSPENSION.
• SUGAR DISSOLVED IN WATER IS A SOLUTION.
• CAN YOU NAME SOME DIFFERENTS BETWEEN THEM?
SOME OBSERVED DIFFERENCES
•
•
•
•
DIFFERENCES IN CLARITY !
DIFFERENCES IN UNIFORMITY !
DIFFERENCES IN SETTLING !
DIFFERENCES IN FILTRATION !
CLARITY
• SOLUTIONS ARE TRANSPARENT *
• SUSPENSIONS ARE OPAQUE *
•
* ALTHOUGH SOLUTIONS ARE TRANSPARENT (YOU CAN SEE THROUGH
THEM) THEY MAY BE COLORED
•
* OPAQUE MEANS CLOUDLY
UNIFORMITY
• UNFORMITY OR HOMOGENOUS MEANS THE SAME
THROUGHOUT
• SOLUTIONS ARE HOMOGENOUS ( THE SAME AMOUNT OF
DISSOLVED SUBSTANCE FOR THE SAME AMOUNT OF
SOLUTION EVERYWHERE IN THE SYSTEM)
• SUSPENSIONS ARE HETEROGENOUS (THE AMOUNT OF
SUSPENSED MATERIAL DIFFERS FROM PLACE TO PLACE)
• FOR EXAMPLE, THE AMOUNT OF MUD IS MORE
CONCENTRATED AT THE BOTTOM THAN AT THE TOP
SETTLING OUT
• SOLUTIONS NEVER SETTLE. THE
DISSOLVED MATERIAL WILL NOT FALL
OUT OF THE SOLUTION (UNLESS THE
TEMPERATURE IS CHANGED)
• IN SUSPENSIONS, EVENTUALLY THE
SUSPENDED MATERIAL WILL FALL TO
THE BOTTOM OF THE CONTAINER !
FILTRATION
• THE DISSOLVED MATERIAL IN A
SOLUTION CANNOT BE FILTERED OUT BY
ORDINARY MEANS (FOR EXAMPLE THE
SALT CANNOT BE FILTERED FROM SEA
WATER WITH FILTER PAPER)
• IN A SUSPENSION SUCH A MUDDY WATER,
THE SUSPENDED SUBSTANCE CAN BE
FILTERED LEAVING A CLEAR LIQIUD
SOLUTIONS VS. SUPSENSIONS
•
•
•
•
•
• SUSPENSIONS
SOLUTIONS
(1) TRANSPARENT
(2) HOMOGENOUS
(3) WILL NOT SETTLE OUT
(4) CANNOT BE FILTERED
•
•
•
•
(1) OPAQUE
(2) HETEROGENOUS
(3) WILL SETTLE OUT
(4) CAN BE FILTERED
FOG
COLLOIDAL
SUSPENSION
WHAT IS A SOLUTION ?
• DEFINITION: A SOLUTE DISSOLVED IN A
SOLVENT (FOR EXAMPLE A SUGAR / WATER SOLUTION)
• SOLUTE IS THE DISSOLVED SUBSTANCE (THE SUGAR)
• SOLVENT IS THE DISSOLVING MEDIUM IN WHICH
THE SOLUTE IS DISSOLVED (THE WATER)
WHAT COMBINATION OF PHASES CAN FORM
SOLUTIONS ?
• THINK OF SOME DIFFERENT KINDS OF SOLUTIONS. THEY MUST
HAVE THE PROPERTIES OF SOLUTIONS TO BE CONSIDERED.
• SOME COMMON COMBINATIONS: SOLID SOLUTE / LIQUID SOLVENT
(SUGAR DISSOLVED IN WATER)
• LIQUID SOLUTE / LIQUID SOLVENT (ANTIFREEZE DISSOLVED IN
WATER)
• GAS SOLUTE / LIQUID SOLVENT (SODA WATER – CARBON DIOXIDE
DISSOLVED IN WATER)
• GAS SOLUTE / GAS SOLVENT ( AIR – OXYGEN DISSOLVED IN
NITROGEN)
WHAT ARE THE GENERAL CLASSIFICATIONS OF SOLUTIONS
?
• THERE ARE GENERALLY TWO TYPES:
ELECTROLYTES AND NON ELECTROLYTES
• ELECTROLYTIC SOLUTIONS ARE ELECTRICALLY
CONDUCTIVE. THEY CONSIST OF IONIC SOLUTES
DISSOLVED IN POLAR SOLVENTS
• NON ELECTROLYTIC SOLUTIONS ARE NON
CONDUCTIVE AND THEY CONSIST OF
MOLECULAR SOLUTES DISSOLVED IN NON
POLAR SOLVENTS.
TYPES OF ELECTROLYTIC SOLUTIONS
• STRONG ELECTROLYTES
• SOLUTIONS IN WHICH ALL OF THE DISSOLVED
SOLUTE FORMS IONS
• WEAK ELECTROLYTES
• SOLUTIONS IN WHICH ONLY A PERCENTAGE OF
THE DISSOLVED SOLUTE FORMS IONS
OTHER WAYS TO CLASSIFY SOLUTIONS
• SATURATED SOLUTIONS
• NO MORE SOLUTE CAN BE DISSOLVED
(SOLUBILITY LIMIT HAS BEEN REACHED)
• UNSATURATED SOLUTIONS
• ADDITIONAL SOLUTE CAN STILL BE DISSOLVED
WHAT DETERMINES THE SATURATION
POINT OF A SOLUTION ?
• (1) THE TYPE OF SOLUTE AND SOLVENT
USED
• (2) THE TEMPERATURE OF THE SOLUTION
(Generally solids dissolve better at higher
temperatures while gases dissolve more poorly)
• (3) GAS PRESSURE WHEN A GAS IS THE
SOLUTE (HENRY’S LAW)*
• *THE SOLUBILITY OF A GAS IS DIRECTLY
RELATED TO THE PRESSURE OF THAT GAS
ABOVE THE SOLUTION
•
Solubility = a constant x Pressure of the gas
How Temperature Effects Solubility
Note that all substances (even solids), do not dissolve
better at higher temperatures although most do.
HOW CAN THE SOLUTIONS COMPOSED OF THE
SAME SUBSTANCES BE DIFFERENT
?
• FOR EXAMPLE, HOW CAN ONE AQUEOUS* SUGAR
SOLUTION BE DIFFERENTIATED FROM ANOTHER ?
• DIFFERENT SOLUTIONS CONSISTING OF THE SAME
SOLUTE / SOLVENT COMBINATIONS MAY BE
DIFFERENT IN CONCENTRATION !
• WHAT DOES CONCENTRATION MEAN ??
• * AQUEOUS MEANS THAT WATER IS THE SOLVENT
MEDIUM IN THE SOLUTION
CONCENTRATION
• CONCENTRATION REFERS TO A RATIO OF SOLUTE
AMOUNT TO SOLVENT OR SOLUTION AMOUNT.
• FOR EXAMPLE, CONCENTRATED ORANGE JUICE
MEANS THAT THE SOLUTE (THE ORANGE
COMPONENT) IS PRESENT IN LARGE QUANTITY
RELATIVE TO THE SOLVENT (THE WATER
COMPONENT).
METHODS OF MEASURING
SOLUTION CONCENTRATION
• DEPENDING ON THE UNITS OF MEASURE AND THE
WHETHER SOLVENT OR SOLUTION QUANTITIES ARE
MEASURED, CONCENTRATION CALCULATIONS VARY.
• WHEN THE SOLUTE QUANTITY IS MEASURED IN MOLES
AND THE SOLUTION VOLUME IS MEASURED IN LITERS,
THE CONCENTRATION IS EXPRESSED AS MOLARITY OR
MOLES PER LITER OF SOLUTION.
• MOLARITY = MOLES OF SOLUTE / LITER OF SOLUTION
MOLARITY CALCULATIONS
• WHAT IS THE MOLARITY OF A SOLUTION WITH A VOLUME
OF 2.0 LITERS AND CONTAINING 90.0 GRAMS OF GLUCOSE
(C6H12O6) ?
• THE DEFINITION OF MOLARITY IS MOLES OF SOLUTE PER
LITER OF SOLUTION !
• STEP I – FIND THE NUMBER OF MOLES OF SOLUTE PRESENT
• 90.0 GRAMS / 180 GRAMS PER MOLE OF C6H12O6 GIVES 0.50
MOLES OF GLUCOSE
• STEP II – MOLARITY = MOLES / LITERS
• 0.50 MOLES / 2.0 LITERS = 0.25 M (CAPITAL M = MOLARITY)
MOLARITY CALCULATIONS
(CONTINUED)
• HOW MANY MOLES OF ZINC CHLORIDE ARE
CONTAINED IN 500 ML OF A 0.20 M SOLUTION?
• SINCE M = MOLES / LITERS,
MOLES = M X LITERS
• 500 MLS = 0.500 LITERS
• MOLES = 0.20 M X 0.500 L = 0.100 MOLES
MOLARITY CALCULATIONS
(CONTINUED)
• HOW MANY GRAMS OF SODIUM CHLORIDE (NaCl) ARE
CONTAINED IN 250 MLS OF A 0.50 M SOLUTION ?
•
STEP I – CALCULATION MOLES AS IN THE PREVIOUS PROBLEM
MOLES = MOLARITY X LITERS
•
•
•
MOLES = 0.50 M X 0.250 L = 0.125 MOLES
STEP II – CONVERT MOLES TO GRAMS
NaCl IS 58.5 GRAMS PER MOLE
•
0.125 MOLES X 58.5 GRAMS PER MOLE = 7.31 GRAMS OF NaCl ARE
CONTAINED IN THE SOLUTION
MOLARITY CALCULATIONS
(CONTINUED)
• HOW MANY MILLILITERS OF A 0.40 M SOLUTION
ARE NEEDED TO OBTAIN 45.0 GRAMS OF GLUCOSE ?
• MOLARITY = MOLES / LITERS
• LITERS = MOLES / MOLARITY
• 45.0 GRAMS / 180 GRAMS PER MOLE = 0.25 MOLES
• LITERS = 0.25 MOLES / 0.40 M = 0.625 LITERS
• 0.625 LITERS = 625 MILLILITERS
SOLUTIONS AND DILUTION
• WHAT DOES DILUTION MEAN ?
• DILUTE MEANS LESS CONCENTRATED
• HOW CAN A SOLUTION BE DILUTED?
• BY THE ADDITION OF MORE SOLVENT (MOST
OFTEN WATER)
• WHAT HAPPENS TO THE ORIGINAL
CONCENTRATION OF THE SOLUTION ?
• IT IS REDUCED !
FINAL
VOLUME
V2
(ORIGINAL
VOLUME
PLUS ADDED
WATER)
M1V1 = M2V2
STARTING
VOLUME
V1
STARTING
MOLARITY
M1
FINAL
MOLARITY
M2
DILUTION CALCULATIONS
• THE DILUTION FORMULA:
• M1V1 = M2V2
•
•
•
•
M1
V1
M2
V2
= ORIGINAL CONCENTRATION OF SOLUTION
= ORIGINAL VOLUME OF SOLUTION (ML OR L)
= CONCENTRATION AFTER DILUTION
= VOLUME OF SOLUTION OF AFTER DILUTION (ML OR L)
(ORIGINAL VOLUME + VOLUME OF WATER ADDED)
DILUTION CALCULATIONS
• WHAT IS THE CONCENTRATION OF 200 ML OF A 0.50 M SUGAR
SOLUTION AFTER 100 ML OF WATER HAVE BEEN ADDED?
• M1 = 0.50 M , V1 = 200 ML
• V2 = 200 ML + 100 ML = 300 ML, M2 = ?
• M1V1 = M2V2
• (0.50) x (200) = M2 x (300)
• M2 = 0.33 M
DILUTION CALCULATIONS
(continued)
• HOW MUCH WATER MUCH BE ADDED TO 500 ML OF A 2.0 M SOLUTION
OF GLUCOSE TO DILUTE IT TO A CONCENTRATION OF 0.50 M ?
•
•
M1 = 2.0 M ,
V2 = ?
,
V1 = 500 ML
M2 = 0.50 M
• M1V1 = M2V2
•
•
•
•
(2.0) x (500) = (0.50) x V2
V2 = 2000 ML
NEW VOL OF SOLUTION – ORIGINAL VOL = VOL OF WATER ADDED
2000 ML - 500 ML = 1500 ML ADDED