Chapter 7: Solutions and Colloids

Suggested Problems:

4, 16, 20-28, 46, 48, 52-56, 64, 66,

72, 74, 92

What is a Solution?• A solution is a homogeneous mixture comprised

of one or more solutes dispersed at an atomic, ionic or molecular level uniformly throughout a medium called the solvent

• Solvent: Is the most abundant substance in a solution

• Solute: Are all of the other components that comprise the solution– Notice I did not say dissolved in the solvent

Importance of Solutions

• Most medicines are given as solutions• Most chemistry occurs in solution, rather

than in a pure state• Focus of this chapter

– Solution concentrations– Properties of solutions

Describing Solutes• Solubility: The maximum amount of solute than

can be dissolved in a specific amount of solvent under specific conditions of temperature and pressure

• Soluble Substance: is a substance that dissolves to a significant extent in the solvent

• Insoluble Substance: A substance that does not dissolve to a significant extent in a solvent

• Immiscible: A term used to describe liquids that are insoluble in each other

Describing Solutions

• Saturated: A solution that has the maximum amount of solute dissolved in a given amount of solvent

• Super Saturated: A solution that has a solute dissolved at a greater amount than the solubility of that solute

Process of Solution Formation• Ionic Solutes: Need Polar solvent • IMF’s between solute/solvent > solute/solute

Process of Solution Formation

• Molecular Solutes: Need proper solventPolar if Polar solute Non-polar if Non-polar solute

Dissolved gases: O2, N2

Solution Concentrations: Percent Definitions

100%solution of mLsolute grams %(w/v)

100% olumesolution v

volumesolute %(v/v)

100%masssolution

mass solute %(w/w)

100 x totalpart %

solvent mass solute mass masssolution

100% masssolution

mass solute (w/w) %

• Beware of question wording– If solute is added to enough solvent to make a

solution of a certain volume• This volume is the volume of solution

– If problem states a volume of solute is added to a volume of solvent• Then you need to add the two volumes to get

volume of solution

solvent of volume solute of volumesolution of volume

100% solution of volumesolute of volume (v/v) %

• Remember that percentages are best used if based out of a total of 100– This is true whether it be mass or volume

• For example a 5 % (w/v) solution– This is the same as saying:

100% solution of mL

solute of mass (w/v) %

solution mL 100solute grams 5

Percent Example

• What is the percent (w/v) concentration of a solution prepared by dissolving 45 grams of glucose in enough water to give 300.0 mL of solution?

Percent Example

• Normal saline is 0.89% (w/v) NaCl in water. What volume of normal saline is required to deliver 45 grams of NaCl?

Percent Example

• D-5-W is 5.0% (w/v) dextrose in water. How many grams of dextrose are contained in 1500.0 mL D-5-W?

Solution Concentrations: Molarity

• Useful unit in dealing with chemicals in solution

solution Lsolute molesM

Molarity Example• What is the molarity of a solution prepared by

dissolving 58.5 grams of Cu(NO3)2 in enough water to give a total volume of 500.0 mL?

Molarity Example

• How many moles of HCl are contained in 750.0 mL of a 2.5 M solution?

Titration• A titration is a chemical analysis

that uses volume and molarity• In simple acid-base titrations, you

can use this equation*:MacidVacid= MbaseVbase

• *must be a 1:1 stoichiometric reaction or else this equation does not work

Titration Example• A 25 mL sample of vinegar (which

contains acetic acid) is titrated with 0.100 M NaOH. If 6.75 mL of NaOH are required, what is the molarity of the acetic acid in vinegar?

25 mL of vinegar

0.100 M NaOH

Dilutions• Many reagents and medicines are

available as “stock” solutions that must be diluted prior to use

• In any dilution, you can always use this equation:

C1V1=C2V2

C = concentration V = volume

Example

• If 8.33 mL of 12 M HCl are diluted with water to give a new volume of 1000.0 mL, what is the molarity of the resulting solution?

Example

• How many mL of 5.0% NaCl solution are needed to prepare 5.0 Liters of normal saline?

Electrolytes• Strong electrolytes dissolve 100% in water

to afford solutions that conduct electricity

– Soluble ionic compounds– Strong acids (HCl, H2SO4, HNO3)

Weak Electrolytes

• Weak electrolytes dissociate less than 100% into ions when dissolved in water and produce solutions with varying ability to conduct electricity

– Weak Acids (H3PO4, HF, H2S)

Non-Electrolytes

• When molecular compounds (covalently bonded compounds) dissolve in water, no ions are produced, so the solution does not conduct electricity

Colligative Properties of Solutions

• Colligative properties are those properties that depend on the concentration of the solute, not the identity of the solute

• Examples:– Electrical Conductivity– Vapor Pressure– Boiling Point– Freezing Point

Freezing Point Depression• The freezing point of a solution goes down as the

concentration of solute increase

• Should use molality solution ofMolarity M

solventgiven afor constant Kmoles ofnumber n

solution andsolvent pure ofpoint freezingin difference t

MnKt

f

f

ff

Freezing Point Depression Example

• Calculate the freezing point of a solution comprised of 171 g of C12H22O11 dissolved in enough water to have a final volume of 1.00 L.

Boiling Point Elevation• The boiling point of a solution increases as the

concentration of solute increases

• Should use molalitysolution ofMolarity M

solventgiven afor constant Kmoles ofnumber n

solution andsolvent pure ofpoint boilingin difference t

MnKt

b

f

bb

Boiling Point Elevation Example

• If 13.4 g of NH4Cl is dissolved in water to form a 500.0 mL solution, what is the new boiling point of this solution, assuming that water boils at 100 oC?

Osmotic Pressure

• The osmotic pressure of a solution increases as the concentration of solute increases

Diffusion• Diffusion is the movement of a substance

from an area of high concentration to an area of low concentration

Osmosis• Osmosis is diffusion of water through a

semipermeable membrane• Solute particles are too big (or too polar) to

make it across the membrane• This is how water gets moved around cells

Hydrostatic Pressure

– As the water level rises so does the hydrostatic pressure against the membrane, until a pressure is reached that causes the net movement of water to equilibrate and the volume levels of the two sides become constant

Osmotic Pressure• Osmotic Pressure () is the hydrostatic pressure

required to stop the flow of a solvent from low concentration to high concentration

=nMRT

n = moles of particles obtained when one mole of solute dissolvesM= molarity of the solutionR = is the ideal gas constantT = the temperature in KelvinnM = Osmolarity, a term used in biology and medicine

Tonicity

• Isotonic solutions have equal concentrations of solute particles

• A hypertonic solution has a greater concentration of solute

• A hypotonic solution is a lower concentration of solute

Example

Na+

H2O

Cl-

Hypertonic solutionLess water

Na+

H2O

Cl-

Hypotonic solutionMore water

Direction of osmosis

SPMWhich direction will the water diffuse?

Question• What will happen to a red blood cell when

it is placed into pure water? Cells are isotonic with normal saline (0.89% NaCl). Hint: think about the flow of H2O.

• Hemolysis

Question

• What will happen to a red blood cell when it is placed into 10% aqueous sodium chloride? Cells are isotonic with normal saline (0.89% NaCl)