Water The Universal Solvent

Predict the % water in the following foods

88% water 94% water 94% water 85% water 85% water 86% water

What is Water? Each hydrogen is covalently bonded to oxygenEach hydrogen is covalently bonded to oxygen polar covalentpolar covalent

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 Intermolecular force of attraction between water molecules due to its polarity.Intermolecular force of attraction between 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 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 Inward pull or forces due to hydrogen bonds.Inward pull or forces due to 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 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

Adhesion, Cohesion Cohesion causes water to form drops, surface tension causes them to be nearly spherical, and adhesion keeps the drops in placeCohesion causes water to form drops, surface tension causes them to be nearly spherical, and adhesion keeps the drops in placeCohesion surface tensionCohesion 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.

Meniscus In Glass In Plastic

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. 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 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.

Universal Solvent Why is water the universal solvent?Why is water the universal solvent?