Solutions

Water’s Unique Properties

• There are strong forces of attraction between molecules of water. Hydrogen bonds

• Water is a polar molecule• Water is amphoteric (can act as both acid &

base)• Water exists as a liquid over a wide temp range. • Liquid water changes temperature slowly. High

specific heat• Liquid water can dissolve a variety of

compounds.• Water expands when it freezes.

Attraction Between Molecules• There are strong forces of attraction

between molecules of water.• Hydrogen bonds• Result in many distinctive properties

Liquid state

Exists in liquid state over wide range of temperatures:

32° F to 212° F

This is important because most biological processes require liquid water.

Unique Role of Water in Biological Systems

It makes up about 70% of the human body

It takes up about 71% of the Earth’s surface.

• Water is critical to virtually all cellular function– Metabolism– Diffusion– Osmosis– Transport– Reproduction– Lubricant– Volume – Cellular respiration: C6H12O6 + O2 → CO2 + H2O + energy

– Photosynthesis: CO2 + H2O + sunlight → C6H12O6 + O2

Key Role in Biological Systems

High Heat Capacity

• Water warms & cools slower than surrounding land

• Helps moderate earth’s climate

Universal Solvent: • Water can dissolve many

substances.• Carry nutrients• flush wastes• distribute particles• facilitate other cycles• Unfortunately, it can

become polluted by water-soluble wastes & transport wastes thru ecosystem

                                                                    

Expands When Frozen• Ice has a lower density than liquid

water. Thus, ice floats on water.• One of the only exceptions to

thermal expansion

Surface tension• Surface behaves like

an elastic membrane• Cohesion – water

molecules stick to each other

Capillary actionLong narrow columns of

water rise through roots to leaves

Adhesion – watermolecules stickto other surface

What are solutions?• Homogeneous mixtures

containing 2 or more substances called the solute and the solvent.

Solute

• When you look at a solution it is impossible to tell the solute from the solvent

Solvent

Solutions

• Solute- what is being dissolved• Solvent- the dissolving medium (causes the

dissolving)• Solution- the resulting homogeneous mixture• Aqueous Solution - water is solvent• Dilution – adding more solvent = less concentrated

Universal Solvent• Water is the most

common solvent among liquid solutions

• H2O is polar, having a slightly positive charge on the hydrogen end and negative charge on the oxygen end.

• Because water is polar it dissolve other polar and ionic compounds

Dissolution or Solvation of Solid Solute = Dissolving

Happens only on the surfaceWater molecules surround, attract, and pull ions or

molecules into solution

Like dissolves Like• Polar substances dissolve polar • Nonpolar substances dissolve nonpolar

• Water is polar…which of the above will dissolve in H2O

GlucoseMineral OilIsopropyl Alcohol

Solubility• Solubility is maximum amount of solute that

will dissolve in solvent at a set of condition• Soluble - A substance that dissolves in a

solvent ex. Salt and water

• Insoluble - A substance that does not dissolve ex. Sand and water

• Miscible – 2 liquids that are soluble• Ex. Alcohol and water

• Immiscible – 2 liquids that aren’t soluble

• Oil and Water

Factors Affecting Solubility&

Rate of Dissolution (Dissolving)

1. Nature of Solute / Solvent. - Like dissolves like Polar dissolves polar; nonpolar dissolves nonpolar

2. Temperature - affects velocity of particles

3. Pressure4. Agitation = Stirring – disperses particles

5. Surface Area: crushing increases surface area on which dissolving can occur

Sugar cubes vs

Granulated sugar

Factors Affecting Solubility&

Rate of Dissolution (Dissolving)Solid Solute in Liquid solvent

Gas Solute in Liquid solvent

Ex. Sugar in Tea Ex. CO2 bubbles in soda

Temperature ↑

Pressure ↑

Agitation – ↑ Stirring

Surface Area – ↑ Crush

↑ ↓N/A ↑

↑ ↓

↑ N/A – can’t crush a gas!

General Solubility Rules• Use STAAR

Chart to determine Which Ionic compounds are soluble and insoluble

• NaNO3

• AgCl• Be3(PO4)2

• Na3PO4soluble

insoluble

soluble

insoluble

Types of Solutions

1. Electrolytes – ionic compounds dissolve into ionsconducts electric currentthe more ions → stronger current

2. Nonelectrolytes – molecular compounds: stay molecules in solutionno ions → do not conduct current

Nonelectrolyte Weak electrolyte Strong electrolyte

Electrolytes in the Body

Carry messages to and from the brain as electrical signals

Maintain cellular function with the correct concentrations

electrolytes

Types of Solutions1. Saturated Solution: Full2. Unsaturated Solution: not full3. Supersaturated Solution: overly Full, crystals

will form when disturbed

Saturated Solution• Contains the maximum amount of

dissolved solute for a given amount of solute at at specific temperature

• No more will dissolve• Will be a point on the line of a Solubility

Graph

Ex. NaClO3 at 40°

Unsaturated solution• contains less dissolved solute for a given

temperature and pressure than a saturated solution

• More can be dissolved• Will be a point under the line on graph

Ex. NaClO3 at 40°

Supersaturated solution• contains more dissolved solute than a

saturated solution at the same temperature

• Contains more than it should• Will precipitate if disturbed• Will be a point above the line

Ex. NaClO3 at 40°

Saturated solution to supersaturated solution

• http://www.youtube.com/watch?NR=1&v=1y3bKIOkcmk&feature=fvwp

Solubility Graph

Determine type of solution:

30 grams of NaCl at 10°C Unsaturated30 grams of K2Cr2O7 at50°C Saturated50 grams of KCl at 40°C Supersaturated

Concentration of SoluteConcentration of Solute

The amount of solute in a solution is given by its concentration.

Molarity (M) = moles soluteLiters of solution

EX: A liter of solution containing 0.1 mole of solute is a 0.1 M solution

A 100.5ml intravenous, IV, solution contains 5.10g of glucose (C6H12O6). What is the molarity of this solution?

Mass of solute = 5.10g C6H12O6

Volume of solution = 100.5mlMolarity = ?

1st – calculate the # of moles

180.16g C6H12O6

2nd – convert milliliters into liters (1000 ml = 1 L)

100.5ml = ______________L0.1005

3rd – use formula to solve

Molarity = Moles of solute =

Liters of solution

0.0283

.1005= 0.282M

= 0.0283 mol C6H12O65.10g C6H12O61 mole C6H12O6

V1M1 = V2M2

Because total # of moles of solute does not change during dilution:

moles in stock solution = moles after dilution, so: Molarity decreases as Volume increases

DilutionQuite often, however, solutions are prepared by diluting a more concentrated solution. For example, if you needed a one molar solution you could start with a six molar solution and dilute it. The number of moles of solute stays the same. You have simply increased the amount of solvent in the solution

What volume of a 3.0 M KI stock solution would you use to make a 0.50 L of a 1.5M KI solution???

1st : Make a listM1 = 3.0 MV1 = ?V2 = 0.50 LM2 = 1.5 M

Then plug into formula: V1M1 = V2M2

V1 (3.0) = 0.50(1.5)

And solve for V1 = 0.50(1.5) 3.0

= 0.25 L