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Chapter 4-1

Chapter 4-1. Water. Properties of Water. All cells contain water. About two thirds of the molecules in our body are water. Water provides a medium in which other molecules can interact. Water exists as all three states/phases of matter. Water expands when it freezes. Water is Polar.

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Chapter 4-1

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  1. Chapter 4-1 Water

  2. Properties of Water • All cells contain water. • About two thirds of the molecules in our body are water. • Water provides a medium in which other molecules can interact. • Water exists as all three states/phases of matter. • Water expands when it freezes.

  3. Water is Polar • 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!

  4. 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. • Adhesion – Intermolecular force of attraction between different molecules. • Water molecules cling to other molecules – Meniscus in a graduated cylinder.

  5. 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

  6. 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).

  7. Water’s role in solutions • Solution– small particles are dispersed in mixture, all components are evenly distributed. • Solute the substance that is dissolved. • Solvent the substance that does the dissolving. • Water acts as a solvent to dissolve solutes (ex. sugar) forming solutions.

  8. Water’s role in solutions • Water dissociates - breaks down forming charged particles called ions (H+ and OH-) when its bonds are broken. H2O ----- H+ + OH- • Other compounds also dissociate (break down into their individual ions) when dissolved in water. Ex. NaCl ------> Na+ + Cl-

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