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Covers more than 75% of the Earth’s surface Most important inorganic compound for living organisms Most cellular activities take place in water solutions, cells themselves are about 70% - 95% water. Properties of Water. Properties of Water.
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Covers more than 75% of the Earth’s surface • Most important inorganic compound for living organisms • Most cellular activities take place in water solutions, cells themselves are about 70% - 95% water. Properties of Water
Properties of Water • 4 properties of water that facilitate an environment for life: 1. Cohesive behavior 2. Ability to moderate temperature 3. Expansion upon freezing 4. Versatility as a solvent
1. Cohesive Behavior • Water is a polarmolecule - molecule has slight charge (+ or -) on each end due to uneven distribution of electrons.
Oxygen pulls hydrogen’s electrons closer to it therefore the oxygen atom is slightly negative and the hydrogen becomes slightly positive. • This is the most important property of water! • Allows a strong attraction between water molecules or between water and other polar molecules!
Water clings to itself & other molecules -Cohesion– Intermolecular force of attraction between like molecules. • Water molecules cling to other WATER molecules (hydrogen bonding) • – Beading of water on a smooth surface • -helps the transport of water against gravity in plants • Adhesion – Intermolecular force of attraction between different molecules. • Water molecules cling to other molecules – Meniscus in a graduated cylinder.
2. Moderation of Temperature • Water has a high specific heat-can absorb or release a great deal of heat energy before changing temperature. • Protects organisms from overheating and freezing.
3. Expansion Upon Freezing Freezing point- the temperature at which a liquid changes state to a solid Temperature- a measure of the average kinetic energy (energy of motion) of particles in a sample of matter. -can determine the rate at which chemical reactions occur -measured in oC (degrees Celsius)
-Ice floats in liquid water • -hydroen bonds in ice are more “ordered”, making ice less dense • -If ice sank, all bodies of water would eventually freeze solid, making life impossible on Earth.
4. Versatility as a solvent: Water is good at forming mixtures • Due to slight charge of water molecules. • Mixture- substance composed of two or more elements or compounds that are mixed together but not chemically combined (are not linked by chemical bonds). • Examples: salt and pepper stirred together; atmosphere. • Two types of mixtures: Solutions & Suspensions
Water’s role in suspensions • Suspension– a mixture where the solute does not fully dissolve. • Solute will settle out. • Example blood (plasma and blood cells).
Water’s role in solutions • Solution– small particles are dispersed in mixture, all components are evenly distributed. • Solute the substance that is dissolved. • Solventthe substance that does the dissolving. • Water acts as a solvent to dissolve solutes (ex. sugar) forming solutions. • Aqueous solution- solution in which water is the solvent
Water’s role in solutions -water is a versatile solvent due to its polarity, which allows it to form hydrogen bonds easily. -water can dissolve ionic compounds, and nonionic polar molecules. -large polar molecules (such as proteins) can dissolve in water if they have ionic and polar regions. Hydrophilic substance- has an affinity to water -”water loving” Hydrophobic substance- does not have an affinity to water -”water hating”
