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

• SOLUTIONS

• (1) TRANSPARENT• (2) HOMOGENOUS• (3) WILL NOT SETTLE OUT• (4) CANNOT BE FILTERED

• SUSPENSIONS

• (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 SolubilityNote 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 !

STARTINGVOLUME

V1

STARTINGMOLARITY

M1

FINALVOLUME

V2

(ORIGINALVOLUME

PLUS ADDEDWATER)

FINAL MOLARITY

M2M1V1 = M2V2

DILUTION CALCULATIONS

• THE DILUTION FORMULA:• M1V1 = M2V2

• M1 = ORIGINAL CONCENTRATION OF SOLUTION

• V1 = ORIGINAL VOLUME OF SOLUTION (ML OR L)

• M2 = CONCENTRATION AFTER DILUTION

• V2 = 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 , V1 = 500 ML

• V2 = ? , 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