WaterThe Universal SolventThe Universal Solvent

Predict the % water in the following foods

Predict the % water in the following foods

88% water88% water

94% water94% water

85% water85% water

86% water86% water

What is Water?•Each hydrogen is covalently Each hydrogen is covalently

bonded to oxygenbonded to oxygen

•polar covalentpolar covalent

Water• Water makes up 66% of the human body by Water makes up 66% of the human body by

massmass• We lose it by breathing, perspiration and in We lose it by breathing, perspiration and in

our wasteour waste• If you are inactive you probably lose 25 – 100 If you are inactive you probably lose 25 – 100

ml/hourml/hour• This increases to 3000 ml/hour if you are This increases to 3000 ml/hour if you are

exercising!exercising!• Therefore, you need to replenish your water Therefore, you need to replenish your water

often when exercising to prevent dehydrationoften when exercising to prevent dehydration

The Water Cycle

Hydrogen Bonding

• Intermolecular force of attraction between Intermolecular force of attraction between water molecules due to its polarity.water molecules due to its polarity.

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• Solid less dense than liquid.Solid less dense than liquid.

Surface Tension• Ever noticed that you can fill a glass Ever noticed that you can fill a glass

so that the liquid bulges above the so that the liquid bulges above the rim?rim?

• Insects can walk on water as if it has Insects can walk on water as if it has a skin, but a needle will break a skin, but a needle will break through water immediately and sink?through water immediately and sink?

• These are examples of surface These are examples of surface tensiontension

Surface Tension

• Inward pull or forces due to Inward pull or forces due to hydrogen bonds.hydrogen bonds.

• liquid water acts like it has a skin.liquid water acts like it has a skin.• Water forms round drops.Water forms round drops.

Surface TensionThree 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

Adhesion, Cohesion

• CohesionCohesion causes water to form drops, causes water to form drops, surface tensionsurface tension causes them to be causes them to be nearly spherical, and nearly spherical, and adhesionadhesion keeps keeps the drops in placethe drops in place

Surface Tension

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

MeniscusIn Glass

In Plastic

Ice

• Most liquids contract (get smaller) Most liquids contract (get smaller) as they are cooled.as they are cooled.

• They get more dense.They get more dense.• Ice floats in water.Ice floats in water.• 10% less dense than water.10% less dense than water.• Water freezes from the top down.Water freezes from the top down.

Ice• Water becomes more dense as it Water becomes more dense as it

cools until it reaches 4ºC. cools until it reaches 4ºC. • Then it becomes less denseThen it becomes less dense..• As the molecules slow down they As the molecules slow down they

arrange themselves into arrange themselves into honeycomb shaped crystals.honeycomb shaped crystals.

• These are held together by H-These are held together by H-bonds.bonds.

Universal Solvent

• Why is water the universal Why is water the universal solvent?solvent?