pH and Water Lab Read pages 13-17 in lab manual disassociation Water molecule Hydroxide ion Hydrogen ion

UNIQUE PROPERTIES OF WATER 2/3 of Earth is covered with water Sometimes occurs in all 3 states Liquid, solid, gas

Heats & cools slowly = high _____________ Amount of energy required to heat up ‘Moderates’ Earth’s environments ‘Solvent of life’ Dissolves & carries molecules within organisms Solvent = liquid portion of a mixture Solute = what is dissolved in the solvent

- + Water is a ____ molecule Has opposing charges on each end Result of a polar _______________ O has greater _________________ than H Pulls electrons toward it Shared electrons hover closer to oxygen Polar molecules mix best with other polar molecules Lipids are non-polar e.g., water and ___ do not mix well

Water molecules attach to each other with __________ bonds Weak, short-lived, ______________ Hydrogen bond

Water’s hydrogen bonds at different temperatures: Room temp.: constantly break and reform = _____ Below 32oF: stable & _________ = ice Above 212oF: break entirely = ___ (vapor/steam)

Cohesion When ___ molecules cling together E.g., Surface tension The membrane-like surface of liquids

Adhesion When _______ molecules cling E.g, Capillary action Water ‘wicks’ to sides of containers A ________ is caused by both cohesion & adhesion

Water disassociates into charged ions (H2O) Hydroxide ion (OH-) Hydrogen ion (H+) Solutions can have an abundance of free OH- or H+ Measured as ___

pH: the relative _______ of OH- & H+ Measured on a scale of 0 to 14, __ = “neutral”

Lab Procedures pH of common household solutions Test the pH of various solutions Assign several to each group member No single person should test all solutions Litmus paper will change color according to pH Dip litmus paper into solution using forceps Do not touch the paper with your hands Hand salts will bias your results Record results within 5-6 seconds

Buffers Buffers “tie-up” excess free ions Many biological fluids are “buffered” Why? Compare buffering ability of milk to water Rinse beakers before filling Measure initial pH of each Add 5 drops of dilute acid to each Stir Return dropper to correct vile Measure and record new pH Add 10 drops of dilute base

The energy required to change temperature Specific Heat: The energy required to change temperature Compare specific heat of water and alcohol: 1) Bring water and alcohol to equally low temperature Record that temperature 2) Heat water and alcohol in hot water bath Record changes in temperature over time 3) Cool water and alcohol in ice bath water alcohol

“Mystery” movement of liquids up a tube Capillary action “Mystery” movement of liquids up a tube Compare capillary action of water and alcohol Compare different liquids with one tube diameter Compare different tube diameters in one liquid