3 Water Is essential to life. Covers 70% of earth’s crust, but only 1% is drinkable.In ocean, atmosphere and on land.Found naturally as gas, liquid or solid.67% of our body.
4 What do you know already about Physical properties?Structure and bonding?
5 Physical Properties Colourless,odourless liquid at 25oC Relatively high melting(0oC) and boiling temperature(100oC)High heat capacity - Requires a lot of energy to heat it upHigh latent heatWater expands when frozenDensity of ice less than waterNon-conductorGood solvent for polar compounds
10 Melting and Boiling Temperatures Are higher than similar substances.This is because of the relatively high hydrogen bonding forces.
11 Specific Heat Capacity = energy needed to raise the temperature of 1g of the substance by 1oC.It takes 4.19 J to raise the temperature of 1g water by 1oC.Water requires a large amount of heat to increase its temperature because energy is needed to overcome the H-bonds.
12 Latent Heat Amount of heat needed to change the state of a substance. E.g. When heating ice the temperature remains constant until the ice is melted.Water has a high latent heat because of the hydrogen bonding holding the molecules together.
13 Latent Heat Latent heat of fusion. Energy needed to melt a substance. Latent heat of vaporisation.Energy needed to vaporize a substance.
14 Expansion on FreezingThe regular arrangement of water molecules in ice takes up more space than the irregular arrangement in liquids.Density of ice < density of water.
16 Water As a Solvent Water will dissolve many substances Solutions in water are aqueous solutions (aq).
17 Solution Chemistry In order for substance to dissolve: The particles of the solute are separated from each other.The particles of the solvent are separated from each other.The solvent and solute particles attract each other.
18 Substances That Dissolve 1. Molecular compounds thatA) form hydrogen bondsB) ionise2. Ionic compounds that dissociate
19 Molecular Substances 1A.Those that can form hydrogen bonds with water.E.G. EthanolBoth water and ethanol are polar molecules. They are able to mix freely forming hydrogen bonding between the molecules
20 water hydrogen bonding ethanol Animation (long):hydrogen bondingethanol
22 Molecular Substances 2B.Those that ionise in water. E.g. hydrogen chlorideHCl has a highly polarised bond which breaks in water.This is due to the force of attraction of the water molecules.Two ions are formed
23 Ionisation This process is known as IONISATION. The ions are said to be hydrated.HCl(g) + H20(l) H30+(aq) + Cl –(aq)Hydroniumion
24 Ionic Compounds E.g. NaCl The water molecules are attracted to the ions. They pull the sodium and chloride ions into the surrounding solution.
26 Dissolving Salt H2O is a polar molecule. The charged regions are attracted to ions with the opposite charge.Hence, the positively charged regions of water molecules are attracted to Cl- ions, and the negatively charged regions of water molecules are attracted to Na+ ions.
29 When several water molecules surround an ion in the crystal, the sum of the attractive forces between the water molecules and the ion may become strong enough to overcome the attractive forces between the cations and anions in the NaCl crystal.
37 SolubilityThe maximum amount of a solute that will dissolve in a given quantity of solvent at a particular temperature.Usually measured as mass of solute in 100 g of water.A solution in which no more solute will dissolve is called a saturated solution.
38 Solubility CurvesThe relationship between solubility and temperature can be represented by a solubility curve.Each point on the curve represents as saturated solution. No more solute can be dissolved at that temperature.Saturated solution animationDemo