The Chemistry of Life

Water & Mixtures

copyright cmassengale

Mixtures

• A mixture is a material composed of two or more elements or compounds that are physically mixed but not chemically combined.

Solutions & Solutions & SuspensionsSuspensions

• Water is usually part of a Water is usually part of a mixturemixture..

• Because so many things dissolve Because so many things dissolve in water, it is called the in water, it is called the Universal SolventUniversal Solvent

• There are 3 types of mixtures:There are 3 types of mixtures:– SolutionsSolutions– SuspensionsSuspensions– ColloidsColloids

copyright cmassengale

SolutionsSolutions

• A solution is a homogenous mixture in which 1 or more substances are uniformly distributed in another substance

Copyright Pearson Prentice Hall

Na+

Na+

Cl -

Cl -

WaterWater

When a crystal of table salt is placed in warm water, sodium and chloride ions are attracted to the polar water molecules.

Na+ ions will be attracted to WHAT END of the water molecule?

Properties of SolutionsProperties of Solutions

• Ionic compoundsIonic compounds disperse as disperse as ionsions in water (+ions & - in water (+ions & -ions spread out among polar water molecules)ions spread out among polar water molecules)

• SOLUTESOLUTE– Substance that is being dissolvedSubstance that is being dissolved– Substance dissolved in the solutionSubstance dissolved in the solution– Particles may be ions, atoms, or moleculesParticles may be ions, atoms, or molecules

• SOLVENTSOLVENT– Dissolving Substance for the soluteDissolving Substance for the solute– Substance in which the solute is dissolvedSubstance in which the solute is dissolved

copyright cmassengale

Remember that water is the Universal Solvent!

(Many things dissolve in it)

• Aqueous solution (water = solvent) are universally important to living things and are the most common type of solution in nature

• Tinctures are solution in which the solvent is alcohol is a tincture Ex: iodine tincture

Solutions

• Because solutions are so important for Biology, we will learn a little more about it in detail over the next few slides

copyright cmassengale

Ions and dissociation

•Ions are atoms with a positive or negative charge

Electrolytes

•Solutions that conduct electricity are electrolytes (sodium chloride and silver nitrate)

Non-electrolytes

•Non-electrolytes form solutions that do not conduct electricity (sugar, alcohol, benzene)

Review Questions

• What is a solution?• What are the two parts of a solution?• What are some properties of a

solution? • What’s the difference between an

aqueous solution and a tincture?

Effervescence (fizz)

•The escape of a gas from a liquid is effervescence (example: soda and alka seltzer)

Solubility

•The measure of how much solute can be dissolved in a solvent is solubility

What affects solubility?

•The three main factors that affect solubility are temperature, type and the amount of the solvent

Ways to increase dissolving rate

•In order to increase the rate in which a solution dissolves one could heat the solution, stir it, or crush the solute particles

Concentration

•Solutions can be composed of varying proportions of a given solute in a given solvent --- vary in concentration (measurement of the amount of solute)

• Concentration of a solution is the amount of solute that is dissolved in a solvent

Concentrated vs. dilute

•A solution with a lot of solute dissolved is concentrated

•A solution with a little solute dissolved is dilute

Types of solutions

•A saturated solution contains all the solute it can possibly hold

•An unsaturated solution contains less solute that is possible

Supersaturated solution

•A supersaturated solution can be made to hold more solute than is normal

Review Questions

• Compare a saturated, unsaturated, and a supersaturated solution

• What is solubility and what are the three factors that affect it?

• What are three ways to increase the rate in which a solute dissolves?

copyright cmassengale

Freezing point depression

•Lowering the freezing point of a solution as a result of the dissolved solute (freezing point depression) Ex: antifreeze in water

Boiling point elevation

•Raising the boiling point of a substance by adding solute (salt in water)

Polar vs. non-polar

•A polar molecule has oppositely charged ends (+ and -)

•Non-polar molecules have the same charges on its ends (even electrical distribution)

Rule for dissolving solutes in a solvent

•Like solutes dissolve in like solvents (polar in polar, non-polar in non-polar)

Water

•Water is the universal solvent

•A substance that cannot dissolve in water is usually called insoluble

Hard water vs. soft water

•Hard water contains dissolved metal ions

•Soft water does not contain dissolved metal ions

Review Questions

• What is the difference between polar and non-polar molecules?

• What is the general rule for dissolving solutes?

• What is the difference between hard and soft water?

• How does a solute affect the freezing point and the boiling point?

29

Water-soluble protein

SuspensionsSuspensions

• Some materials do not dissolve when placed in water but separate into pieces so small that they do not settle out easily.

SuspensionsSuspensions

• A suspension is a heterogeneous mixture in which the solute particles are large enough to be seen (solute is suspended)

• Substances that Substances that don’t don’t dissolve but separate dissolve but separate into tiny pieces.into tiny pieces.

• Water Water keeps the keeps the pieces suspendedpieces suspended so so they don’t settle out.they don’t settle out.

• Blood & CytoplasmBlood & Cytoplasm are are suspensionssuspensions copyright cmassengale

Colloid

•A colloid is a homogeneous mixture that is not a true solution (does not separate, solute remains suspended)

Interactions with Non-polar Molecules

• Water Organizes nonpolar molecules.• Nonpolar molecules are hydrophobic (repelled by

H2O)

• Repulsion forces these molecules into particular arrangements.

• Example is the lipid bilayer found in cellular membranes.