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6.2 Explaining Solutions. Intramolecular Bonds – A specific attraction within a molecule (i.e. covalent bonds ) Intermolecular Bonds – Force of attraction between molecules. Water and Its Properties Water is a liquid at room temperature due to strong intermolecular forces
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Intramolecular Bonds – A specific attraction within a molecule (i.e. covalent bonds) Intermolecular Bonds – Force of attraction between molecules
Water and Its Properties Water is a liquid at room temperature due to strong intermolecular forces It is a very successful solvent because it is small in size, highly polar, and capacity for hydrogen bonding These properties are very significant for life on Earth
High Melting and boiling point permits water to exist as a liquid at room temperature Keeps body fluids liquid over a large range of temperatures
Expansion when cooling from 4 °C to 0 °C Causes ice to float Causes water to freeze from the top down, allowing life to continue below it
High surface tension Pulls water into round droplets Allows small insects to “walk on water”
Ability to exchange thermal energy with little change in temperature Has a moderating effect on temperature changes in organisms and the environment
Inability to mix with non-polar compounds Enables organisms to retain water because of a waterproof coating (wax on leaves) Allows organisms to store non-polar substances (e.g. fats, oils)
Dissolving Ionic Compounds Dissociation – the separation of ions that occurs when an ionic compound dissolves 1. As a water molecule approaches the crystal, they reorient themselves because the negative end of each water molecule is attracted to the positive charge in the ionic solid
Next water-ion attractions pull ions away from the crystal while ionic bonds are holding the ions together a) If the attraction between the water and the ionic solid are stronger than the ionic bonds within the ionic solid it will dissolve If not, the crystal remains as an undissolved solid
As the ions from the ionic solid leave the crystal, they become surrounded by a sphere of water molecules so that they cannot attract each other again
Dissolving Molecular Compounds Molecular compounds vary in how easily they dissolve in water Molecular compounds with many hydrogen bonds usually dissolve better
Many substances such as hydrocarbons do not dissolve in water Many hydrocarbons are large, have covalent bonds and are non-polar molecules There are almost no attractive forces between water and hydrocarbons so they do not dissolve
Other non-polar substances are soluble in hydrocarbons L-D forces loosely attract the solute molecules to the hydrocarbon allowing it to dissolve
Like Dissolve Like Solutes dissolve when the attractive forces between solute and solvent are stronger than the attractive forces within either the solute or solvent Polar substances dissolve polar substances and non-polar substances dissolve non-polar substances