Chemical Reactions Properties of Water Solutions Acids, Bases, and pH

PROPERTIES OF WATER The water molecule is a great example of the uneven sharing of electrons The preceding creates some of the unique properties of water like…

PROPERTIES OF WATER Water molecules are unique because… Surface tension High boiling point and low freezing point Density of ice vs. water

PROPERTIES OF WATER HYDROGEN BONDING A force of attraction between molecules Instead of atoms attracting other atoms or molecules, the molecule attracts neighboring molecules Always involves hydrogen attracted to Fluorine Oxygen Nitrogen http://programs.northlandcollege.edu/biology/Biology1111/animations/hydrogenbonds.html

PROPERTIES OF WATER Adhesion and Cohesion Water is attracted to other water. This is called cohesion. Water can also be attracted to other materials. This is called adhesion. The oxygen end of water has a negative charge and the hydrogen end has a positive charge. The hydrogens of one water molecule are attracted to the oxygen from other water molecules. This attractive force is what gives water its cohesive and adhesive properties.

SOLUTIONS Solution - a homogenous mixture. Homogenous - a mixture that is completely uniform in composition; its components are not readily distinguished. Is a dispersion of ultimate-sized (molecules, atoms, ions) particles of solute in solvent.

SOLUTIONS Cannot be separated into solute and solvent by filtration. Is clear (transparent), but may be colorless or colored. Acts as though it is in a single phase.

SOLUTIONS Solute – dissolved particles in solution. Solvent – the dissolving medium in a solution.

SOLUTIONS The solute is the substance, which is being dispersed by the dispersing agent, the solvent. The solute is generally in smaller quantity but in solid/liquid solutions, the solid is generally considered to be the solute regardless of quantities.

SOLUTIONS Both solute and solvent may be solid, liquid, or gas. They may be paired a variety of combinations. Types of solutions Example Solute Solvent solid in liquid salt water salt water gas in liquid ammonia water ammonia gas in gas air oxygen nitrogen solid in solid brass alloy Zinc copper liquid in liquid alcohol solution alcohol

SOLUTIONS In order for a solute and solvent to disperse in one another there must be attractive forces, which are similar to in strength to those, which existed between the solute particles and also between the solvent particles. For this reason ionic (NaCl) or polar solutes (hydrogen Chloride) will dissolve readily in water, a polar solvent. Non-polar solutes such as iodine and hydrocarbon compounds dissolve much more readily in each other than in water. Solubility is a term used to describe the maximum amount of solute, which can dissolve in a given amount of a specific solvent at a given temperature and pressure.

SOLUTIONS “Likes Dissolve Likes.” Useful method for describing the combinations of solutes/solvents which will dissolve readily. -Miscible - describes liquids that dissolve in each other. -Immiscible – describes liquids that are insoluble in one another: oil and water are immiscible.

SOLUTIONS Often water will not mix with molecular liquids like oil. We say that the two liquids are not miscible. They do not mix together or dissolve - they form two separate layers. They have to be shaken up to get them to mix for just a short time. Picture: Oil and water don't mix. They are immiscible. They form two separate layers. Shaking them will mix them for a short time.

SOLUTIONS Saturation amount (solubility) is related to solvent and solute, (polar, non-polar, ionic) temperature, and (in cases where the solute is a gas) pressure. -Dilute – a solution that contains a small amount of solute. -Concentrated – a solution containing a large amount of solute.

SOLUTIONS Unsaturated - a solution that contains less solute than a saturated solution at a given temperature and pressure. Saturated – a solution containing the maximum amount of solute for a given amount of solvent at constant temperature and pressure; an equilibrium exists between undissolved solute and ions in solution. Supersaturated - a solution that contains more solute that it can theoretically hold at a given temperature; excess solute precipitates if a seed crystal is added.

SOLUTIONS Colligative Property – a property of a solution that depends only on the number of solute particles; boiling point elevation, freezing-point depression, and vapor pressure lowering are colligative properties.

Acids and Bases Water dissociates into hydrogen ions (H+) and hydroxide ions (OH-). They ions then re-associate back into water: it’s a constant back-and-forth process, with an equilibrium between the H2O form and the H+ and OH- forms. Acids produce H+ ions when dissolved in water Bases absorb H+ ions when dissolved in water. Water is neutral, neither acid nor base, because it always has equal numbers of H+ ions and OH- ions. Both conditions can speed up various chemical reactions; acids and bases cause most of the chemical transformations that occur in living things. Much of the digestion that occurs in the stomach is due to strong acids (hydrochloric acid) there. ↑ http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/acid13.swf

Acids and Bases To create an acidic condition, dissolve an ionic substance in water that releases H+ ions but not OH-. Similarly, an ionic substance that releases OH- but not H+ is a base. The OH- absorbs the H+ ions already present in the water. An example is lye: sodium hydroxide: NaOH, which dissociates into Na+ and OH-. Bases are also called alkaline. Ammonia and other compounds that contain NH2 also work as bases.

pH Scale Acidity is measured on the pH scale, which indicates the amount of H+ ions present. The scale runs from 0 (very acidic) to 14 (very basic). Water, which is neutral, has a pH of 7 Acids have lower pHs: the hydrochloric acid in your stomach has a pH of about 2. Eating food stimulates your stomach to secrete more acid. Antacids (like Tums or Rolaids) neutralize some of this acid. Bases have a higher pH: the lye in over cleaner has a pH of about 14. Body fluids are slightly basic, pH 7.4 http://www.johnkyrk.com/pH.html

Buffer http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/buffer12.swf