Ch-10 Hard and Soft WaterScience 7th grade

Introduction• .

What is Water Hardness?

Video: https://www.youtube.com/watch?v=emFJltOAfTo

Topic

• .

Groundwater dissolves rocks and minerals releasing calcium, magnesium, and other ions that cause water to be hard. These dissolved

ions give hard water its characteristics.

Hard WaterHard Water

• What do you think the term “hard water” What do you think the term “hard water” means?means?

Note: Note: Water where you live might be hard or soft – this Water where you live might be hard or soft – this depends on the rocks the water meets on its way to you…depends on the rocks the water meets on its way to you…

Hard WaterHard Water

• Hardness refers to the Hardness refers to the presence of calcium and presence of calcium and magnesium ions in water magnesium ions in water (and sometimes iron).(and sometimes iron).

• Ions come from dissolved Ions come from dissolved rock the water has passed rock the water has passed through.through.

• Affects properties of tap Affects properties of tap waterwater

Hard WaterHard Water• Minerals in hard water Minerals in hard water

interact with soap.interact with soap.• Interferes with soap’s Interferes with soap’s

ability to lather.ability to lather.

Topic

• .

Hardness levels vary in different geographic regions.

Topic

• .

So, what’s the big deal?Why is hardness bad?

Module Objectives

It costs youMONEY !!

• Calcium and iron deposits can build up in appliances and on faucets:– Washing machine – Dish washer– Steam iron

• Shortens their life span and adds to landfill problem!

• Hard Water causes damage to the hair.

Hardness minerals precipitate out of the water and form energy robbing

scale.

Wastage of EnergyWastage of Energy

• Most people agree that it tastes better.• It is thought to reduce the number of heart

illnesses.• It provides useful calcium ions for the healthy

growth of bones and teeth.• The formation of lime scale in pipes (see below)

causes the inside of the pipe to be covered with insoluble bicarbonates. This layer prevents the hot water from coming in contact with the surface of the pipe.

• This prevents corrosion of metal and also from dissolving of harmful metals in water.

Positive effects of Hard waterPositive effects of Hard water

Lab activity: Testing for Hard Lab activity: Testing for Hard WaterWater

• Three samples of water– Hard water– Tap water (?)– Distilled water

• Your job is to find out which sample is which!

• 1 beaker• 3 test tubes• Marker• Eyedropper

• Label test tubes with marker and tape:• A B C

• Place 10ml of water in each corresponding test tube

• Observe your 3 samples• Can you tell by observing and touching which

one is hardest?

• Water hardness affects a soap’s ability to lather: the harder the water the fewer soap suds will form.

• How can this fact help you determine which sample is the hardest?

Lab activity: Testing for Hard Lab activity: Testing for Hard WaterWater

• Three samples of water– Hard water– Tap water (?)– Distilled water

• Your job is to find out which sample is which!

Soft WaterSoft Water

• Water with very low concentrations of minerals.• Soap lathers easily and is sometimes difficult to rinse

off.

Distilled WaterDistilled Water

• Water that has been purified through evaporation and condensation so remove minerals such as calcium.

• Is distilled water soft water?Is distilled water soft water?

http://wiki.answers.com/Q/http://wiki.answers.com/Q/How_is_distilled_water_soft_or_hard?#slide=1How_is_distilled_water_soft_or_hard?#slide=1

• Water is hard both temporarily and permanently…

• Temporary hardness if caused by hydrogencarbonate ions (HCO3

-) in Ca(HCO3)2

• Permanent hardness is caused by, amongst other things, dissolved calcium sulfate

Types of Hard WaterTypes of Hard Water

Temporary Hardness

• Temporary hardness is removed by boiling – the Ca(HCO3)2 decomposes forming calcium carbonate which is insoluble (“limescale”)

Ca(HCO3)2(aq) CaCO3(s) + H2O(l) + CO2(g)

Temporary & Permanent Hardness

• Temporary and permanent hardness can be softened by adding washing soda (Na2CO3)

• The carbonate ions react with the calcium ions and magnesium ions making an insoluble precipitate of calcium carbonate and magnesium carbonate

• As the calcium ions and magnesium ions are no longer dissolved in the water they cannot make it hard

Ca+2(aq) + CO3

-2(aq) CaCO3(s)

Temporary & Permanent Hardness

• Temporary and permanent hardness can be softened by running the water through an ion exchange column which contain sodium ions or hydrogen ions which exchange them for calcium ions and magnesium ions

Na2Resin(s) + Ca+2(aq) CaResin(s) + 2Na+

(aq)

• *Resin is a large insoluble resin molecule

Hard water, loaded with Calcium, Magnesium, and many other ions, enters the water softener and contacts millions of special resin beads which hold billions of sodium ions. The Calcium, Magnesium, and other ions trade places with the Sodium ions, creating softened water.

How Water Softeners Work

How Water Softeners WorkSOFTENING CYCLE

Softened water containing

sodium ions

Regeneration with salt brine now required

Partially exhausted, but still delivering 100% soft water

Sodium charged ion

exchange resin

Water Softener

Hard water enters

Many gallons later

Capacity to soften water now ending

How Water Softeners WorkREGENERATION CYCLE

15 to 20 minutes later

Ready for ion exchange softening

Regeneration almost completed

Salt brine, most economical

source of sodium

Waste water containing hardness in

exchange for sodium

Softener still discharging waste water

Excess salt brine also removed

Regeneration complete

Typical Water Softener

Water Softeners Remove Other Contaminants

Nearly any positively charged cation can be captured by a typical water softener using standard cation exchange resin, i.e. Iron, Manganese, Lead, Aluminum, Barium, Cadmium, Copper, Potassium, Radium, Silver, Strontium, Uranium (depending on valence).

This is not a comprehensive list, and specific water chemistry may affect removal rates.

Ever heard of Heavy Water ??

• Heavy water is water that contains heavy hydrogen or deuterium.

• Deuterium differs from the hydrogen usually found in water, Protium, in that each atom of deuterium contains a proton and a neutron.

• Heavy water may be deuterium oxide, D2O or it may be deuterium protium oxide, DHO.

• Heavy water occurs naturally, although it is much less common than regular water.

• Approximately one water molecule per twenty million water molecules are heavy water.

Heavy Water

Conclusion

• Why is distilled water the softest?

• Which water sample is most likely to contribute to water pollution? Explain