2.2 Properties of Water
Do Now
• Describe and draw a picture of a ionic bond• Describe and draw a picture of a covalent bond
2.2 Properties of Water
OHH
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Life depends on hydrogen bonds in water.
• Water is a polar molecule.– Polar molecules have slightly charged regions, due to
uneven pull on electrons.
– Nonpolar molecules do not have charged regions.– Hydrogen bonds form between slightly positive hydrogen atoms and slightly negative atoms.
2.2 Properties of Water
• Hydrogen bonds are responsible for three important properties of water.
– high specific heat– cohesion– adhesion
2.2 Properties of Water
Properties of water related to hydrogen bonds
• High Specific Heat - Large amount of energy needed to produce an increase in temperature.– Important in regulating temperature of cells
• Cohesion - water molecules “stick” to each other– Beads of water– Surface tension
• Adhesion - water molecules “stick” to other substances– Helps transport water from roots to leaves in plants
2.2 Properties of Water
Many compounds dissolve in water.
• A solution is formed when one substance dissolves in another.– A solution is a homogeneous mixture.– Solvents dissolve other substances (greater
concentration).– Solutes dissolve in a solvent (lower concentration).
solution
2.2 Properties of Water
• “Like dissolves like.”
– Polar solvents dissolve polar solutes.– Nonpolar solvents dissolve nonpolar solutes.– Polar substances and nonpolar substances generally
remain separate.– Oil and Water
2.2 Properties of Water
Acids and Bases
• Acids taste sour, are corrosive to metals, change litmus (a dye extracted from lichens) red, and become less acidic when mixed with bases.
• Bases feel slippery, change litmus blue, and become less basic when mixed with acids.
2.2 Properties of Water
Some compounds form acids or bases.
• An acid releases a hydrogen ion when it dissolves in water.– high H+ concentration– pH less than 7
more acidic
stomach acid pH between 1 and 3
2.2 Properties of Water
• A base removes hydrogen ions from a solution.
– low H+ concentration– pH greater than 7
bile pH between 8 and 9
more basic
2.2 Properties of Water
How do Acids and Bases work?
• Water can dissolve compounds into their individual ions
• Acids– Compounds that contain hydrogen and release a
hydrogen ion when put in an aqueous (water) solution• Bases
– Substances that dissolve in water and release hydroxide ions (OH-) into solution.
• Neutralization– acids release H+ into solution and bases release OH-.
If we were to mix an acid and base together, the H+ ion would combine with the OH- ion to make the molecule H2O, or plain water
- Always produces water and a salt
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