Water The Universal Solvent

What is Water? Water – H 2 O – 2 hydrogens, 1 oxygenWater – H 2 O – 2 hydrogens, 1 oxygen Each hydrogen is covalently bonded to oxygenEach hydrogen is covalently bonded to oxygen Pure covalent or polar covalent?Pure covalent or polar covalent? Polar!Polar!

Water Water makes up 66% of the human body by massWater makes up 66% of the human body by mass We lose it by breathing, perspiration and in our wasteWe lose it by breathing, perspiration and in our waste If you are inactive you probably lose 25 – 100 ml/hourIf you are inactive you probably lose 25 – 100 ml/hour This increases to 3000 ml/hour if you are exercising!This increases to 3000 ml/hour if you are exercising! Therefore, you need to replenish your water often when exercising to prevent dehydrationTherefore, you need to replenish your water often when exercising to prevent dehydration

The Water Cycle

Hydrogen Bonding Leads to a higher boiling pointLeads to a higher boiling point Higher melting pointHigher melting point High specific heat capacityHigh specific heat capacity Surface TensionSurface Tension

Surface Tension liquid water acts like it has a skin.liquid water acts like it has a skin. Water forms round drops.Water forms round drops. All because water hydrogen bonds.All because water hydrogen bonds.

Surface Tension One water molecule H bonds to another.One water molecule H bonds to another. Can H bond to molecules all around.Can H bond to molecules all around. H H O ++ ++ -- H H O ++ --

Surface Tension Ever noticed that you can fill a glass so that the liquid bulges above the rim?Ever noticed that you can fill a glass so that the liquid bulges above the rim? Insects can walk on water as if it has a skin, but a needle will break through water immediately and sink?Insects can walk on water as if it has a skin, but a needle will break through water immediately and sink? These are examples of surface tensionThese are examples of surface tension

Surface Tension Three different drops of liquid Pure water – drops are spherical, surface tension means water wants minimum surface area Water + Green Dye – No real effect on surface tension, drops still spherical Water + dish Soap – Hydrogen bonds broken, less surface tension, flat drops

Surface Tension A water molecule in the middle of solution is pulled in all directions.A water molecule in the middle of solution is pulled in all directions.

Surface Tension Not true at the surface.Not true at the surface. Only pulled down and to each side.Only pulled down and to each side. Holds the molecules together.Holds the molecules together. Causes surface tension.Causes surface tension.

Surface Tension Water drops are round because all the molecules on the edge are pulled to the middle.Water drops are round because all the molecules on the edge are pulled to the middle.

Surface Tension Glass has polar molecules.Glass has polar molecules. Glass can hydrogen bond.Glass can hydrogen bond. Attracts the water molecules.Attracts the water molecules. Some of the pull is up.Some of the pull is up.

Meniscus Water curves up along the side.Water curves up along the side. This makes the meniscus.This makes the meniscus.

Meniscus In Glass In Plastic

Heat Capacity Water has a high heat capacity (same as specific heat).Water has a high heat capacity (same as specific heat). It absorbs 4.18 J/g ºC while iron absorbs only J/g ºC.It absorbs 4.18 J/g ºC while iron absorbs only J/g ºC. Remember SH = heat Mass x  TRemember SH = heat Mass x  T Calculate the heat need to raise the temperature of 1g of both iron and water by 75ºC.Calculate the heat need to raise the temperature of 1g of both iron and water by 75ºC.

Heat of vaporization Because of the strong hydrogen bonds it takes a large amount of energy to change water from a liquid to a solid.Because of the strong hydrogen bonds it takes a large amount of energy to change water from a liquid to a solid. 226 J/g is the heat of vaporization.226 J/g is the heat of vaporization. It takes this much energy to boil water.It takes this much energy to boil water. You get this much energy back when it condenses.You get this much energy back when it condenses.

Ice Most liquids contract (get smaller) as they are cooled.Most liquids contract (get smaller) as they are cooled. They get more dense.They get more dense. When they change to solid they are more dense than the liquid.When they change to solid they are more dense than the liquid. Solid metals sink in liquid metal.Solid metals sink in liquid metal. Ice floats in water.Ice floats in water. Why?Why?

Ice Water becomes more dense as it cools until it reaches 4ºC.Water becomes more dense as it cools until it reaches 4ºC. Then it becomes less dense.Then it becomes less dense. As the molecules slow down they arrange themselves into honeycomb shaped crystals.As the molecules slow down they arrange themselves into honeycomb shaped crystals. These are held together by H-bonds.These are held together by H-bonds.

H H O H H O H H O H H O H H O H H O H H O H H O H H O H H O H H O H H O Liquid Solid

Ice 10% less dense than water.10% less dense than water. Water freezes from the top down.Water freezes from the top down. It takes a great deal of energy to turn solid water to liquid water.It takes a great deal of energy to turn solid water to liquid water. Heat of fusion is 334 J/g.Heat of fusion is 334 J/g.