2.2 Properties of Water

Pages 40 - 43

Goal 1:Explain the polarity of water

molecules

• Polar molecule

– A molecule with slightly charged “poles”

– One end is slightly positive

– Other end slightly negative

– Due to uneven distribution of electrons

• Oxygen end – Many protons has stronger hold on electrons– Slight Negative charge

• Hydrogen ends + “naked” protons+ Slight Positive charge Image: PD on wikipedia

http://commons.wikimedia.org/wiki/Image:H2O_(water_molecule).jpg

• Polarity results in Hydrogen bonds forming

– Type of Van der Waals force

– Weak attraction

– Between hydrogen and a negative atom

Image credit: Qwerter, Michal Manas on Wikipedia commons http://en.wikipedia.org/wiki/Image:3D_model_hydrogen_bonds_in_water.jpg

• Hydrogen bonding between water molecules

Image credit: placbo on Flickr

• Cohesion– Attraction

between SAME molecules

– i.e. water & water

Image credit: Mr. Greenjeans on Flickr

http://www.flickr.com/photos/gaylon/298648625/

• Adhesion

– Attraction between different molecules

– Plants use adhesion and capillary

action in Xylem for water transport

Image credit: ShutterSparks on Flickr

http://www.flickr.com/photos/shuttersparks/1413258875/

Image credit: Luc Viatour on wikipedia commons

http://en.wikipedia.org/wiki/Image:Dew_on_a_Equisetum_fluviatile_Luc_Viatour.jpg

• An excellent example of cohesion and adhesion

• Capillary action– Cohesion– Adhesion– (evaporation)

Image credits: http://www.sciencebuddies.org/science-fair-projects/project_ideas/PlantBio_p033.shtml

Goal 2:Distinguish between a solution

and a suspension

Solution

• Solute = substance that dissolves

• Solvent = substance in which solute dissolves

Image credit: Chris 73 on wikipedia

http://en.wikipedia.org/wiki/Image:SaltInWaterSolutionLiquid.jpg

• Solution characteristics– Dissolving– Compounds

separate– Solute does NOT

settle out

Image credit: hundrednorth on Flickr

http://www.flickr.com/photos/100n30th/4821481/

• Suspension– No dissolving /

separation of compounds

– Settling occurs

Image credit: consumatron on Flickr

http://www.flickr.com/photos/consumatron/2514611795/

Goal 3:Explain acidic and basic

solutions

• Hydrogen Ions and hydroxide ions

– Water molecule will separate to form ions

– pH scale measures H+ ion presence

– Copy equation on pg 42 to see why a water molecule forms one of each ion.

• Hydrogen (H+) ions are associated with acids– Recognize acids by the “H” found in the

compound (often found at beginning or end of chemical formula)

H2SO4

HNO3

H3PO4 HCl

• Hydroxide ions (OH-) are associated with bases– Recognize some bases by the “OH” found in

the compound (other bases steal a “H+” from water and leave behind an “OH-” group)

KOH

Ba(OH)2

NaOH

Ca(OH)2

• Acids– Release hydrogen

ions H+ in solution– Concentration of H+

is high– pH 0 – 7– acidic

Image credit: Lou FCD on Flickr

http://www.flickr.com/photos/loufcd/2870399185/

• Bases– Produces OH- in

solution– Less H+ ions than

pure water– pH 7- 14– basic

Image credit: Lou FCD on Flickr

http://www.flickr.com/photos/loufcd/2870399185/

Concentration of H+ ions changes by

powers of 10

pH =1 has 10x more than pH = 2

pH = 1 has 100x more than pH = 3

More Less

1 2 3 4 5 6 7 8 9 10 11 12 13 14

• Buffers

– Weak acid or base

– Neutralizes strong acids or bases

– Prevents sudden changes in pH