Water H2O What do the students think of when they see this picture? Where do we find water? Rivers/Lakes/Oceans/Streams etc.

Test for Water Cobalt Chloride Cobalt Chloride Paper Paper Click on slide to drop water onto blue cobalt chloride paper and it turns pink.

3 States Solid 0˚C Room Temperature 100˚C Liquid Gas Water exists in all three states (phases). Ask the students if they know at what temperature water is present in it’s solid/liquid/gas phase. i.e. question them to see if they know the freezing point and boiling points of water. Click on the slide to reveal the names. A further click shows up the temperatures at which the water exists in these phases. Solid 0˚C Room Temperature Liquid Gas 100˚C

Properties of Water Water is the only liquid that expands when it freezes Ice is less dense than water Ice floats on top Water is an excellent solvent Ask question why does ice float on top? What would you expect a solid to do? Click to add picture of ice Can the students name a solute that is not soluble in water? i.e. oil non-polar substances. Oil in water forms an immiscible solution. = NaCl + Solvent Solution

Water, Water Everywhere! Covers 70% of Earth’s surface Human body is 2/3 water Click to add man

70% of the earth is covered in water but only a small percentage~ 3% is accessible. Water is essential for life! Click on the page to reveal the pie charts.

Water Cycle Water is recycled - Constant supply Evaporation =Turning a liquid into a gas Transpiration = Loss of water from the stomata of a leaf Click on page to reveal definitions. Stomata

Water Cycle

Water as a solvent Tap water contains : - dissolved gases - dissolved solids - suspended (floating) solids How do fish breathe underwater? Dissolved oxygen

To Show that Water Contains Dissolved Solids Water sample Clock glass Water Wire gauze Water is such a good solvent it contains many dissolved solids. Test various water samples using the apparatus as pictured above to determine what dissolved solids they may contain. Test a sample of hard water, soft water, rain water, a stream sample etc. Click on the green question box and it will link to assessment 1. Bunsen burner Tripod

Water Hardness Hard Water Soft Water Scum Bubbles Soft water forms bubbles easily with soap Hard water does not form bubbles easily with soap Ask students as to what type of water is in their area? If they live near a limescale area e.g. Burren they will have hard water. Scum Bubbles

What causes water hardness? Calcium ions dissolved in the water Calcium Carbonate + Rainwater Calcium ions in solution CaCO3 H2CO3 Ca(HCO3)2 (insoluble) (carbonic acid) (soluble) Burren Calcium carbonate is present in limestone areas. Water that contains dissolved Carbon dioxide gas forms carbonic acid The acid dissolves the calcium carbonate to form calcium hydrogen carbonate which dissolves in the water. Students should know the reaction of an acid and a carbonate .

What causes water hardness? Soluble compounds of calcium and magnesium Calcium Hydrogen Carbonate = Ca(HCO3)2 Magnesium Hydrogen Carbonate = Mg(HCO3)2 Calcium Sulphate = CaSO4 Magnesium Sulphate = MgSO4 Click on page to reveal the soluble compounds

To test various water samples for hardness Soap Solution Using the apparatus above add a little soap solution to various water samples in order to determine how easily they form bubbles. A B C D

2 Types of Water Hardness 1. Temporary Hardness Can be removed by boiling Caused by : Ca(HCO3)2 Mg(HCO3)2 2. Permanent Hardness Cannot be removed by boiling Caused by : CaSO4 MgSO4 Click to reveal the compounds that cause temporary and permanent hardness.

Temporary Hardness Boil Removed by boiling Problem: CaCO3 Ca(HCO3)2 The problem with boiling the water is that while the temporary hardness is removed the CaCO3 formed precipitates out of the solution to leave a scale on pipes and kettles. CaCO3 Ca(HCO3)2 Boil Insoluble (Limescale)

Permanent Hardness X Cannot be removed by boiling Can be removed by adding softeners Can be removed by passing water through an ion exchange resin ion exchange resin

Water Softeners Easy method NaCO3 + CaSO4 CaCO3 + NaSO4 Bath salts - Add Sodium Carbonate (Washing Soda) NaCO3 NaCO3 + CaSO4 CaCO3 + NaSO4 does not make water hard insoluble Click to reveal a picture of bath salts Bath salts coloured NaCO3

Ion Exchange Hard tap water ion exchange resin glass wool plug Apparatus required to deionise hard water. Click on black square to reveal movie of ion exchange Soft water

Ion exchange Positive Ca2+ ions in the water swapped for H+1 ions in the resin Negative ions in water replaced by OH- ions in the resin H+ ions and OH- ions Water (H2O) Deionised water Click on page to allow movement of ions between the resin and the water. Ion exchange resins are specially prepared plastic beads. Ca2+ H+ HCO3- OH- Hard water Resin

Advantages of Hard Water Disadvantages of Hard Water 1. Good for brewing Ca needed for healthy teeth and bones Tastes better Blocks pipes and leaves a scale on kettles and boilers Wastes Soap Makes scum with soap Click on page to reveal the advantages and disadvantages one by one.

Advantages of Hard Water Disadvantages of Hard Water Ca for healthy teeth and bones 1. Limescale -blocks pipes and leaves a scale on kettles. 2. Good for Brewing 2. Wastes soap 3. Tastes better 3. Scum produced with soap As before.

Pure Water Distilled water Chemical experiments Car batteries Wash Bottle Click on the green square to reveal assessment questions.

To obtain pure water from seawater Water out Liebig condenser Ask the students if they can list what type of dissolved substances seawater may contain? Click on the green button to reveal assessment questions Water in Seawater Pure water Bunsen

Would you drink this water? Why would the students not drink this water? The colour is off-putting. There may be suspended solids floating in the water. Bacteria and diseases such as typhoid. Would the students drink the water in the second picture? Why is this water more appealing?

6 Steps in Water Treatment Screening Sedimentation Filtration Chlorination Fluoridation pH adjustment Click to reveal the 6 steps Note in the picture the difference between the two water samples

Water Treatment Process

1. Screening 2. Sedimentation Water is stored in large settling tanks. Removal of large pieces of dirt and rubbish.

3. Sedimentation 4. Filtration Flocculating agent added e.g. Alum that forces small dirt particles to clump together. Very small particles are removed when water is passed through the filtration beds.

4. Chlorination 5. Fluoridation Cl2 F2 Note: The students have heard about chlorine at the swimming pool. The students know that fluoride is added to toothpaste. Chlorine gas is added to kill any bacteria. Fluorine compounds are added to help prevent tooth decay.

6. pH adjustment Lime Lime is basic and so it raises the pH of the water Lime is added to acidic water to increase the pH.

H2O H H Bonds join the H atoms to the O atom O

Breaking Bonds Electrolysis Cannot break the H20 molecules by heating Have to break the bonds joining the oxygen and the hydrogen atoms to free the atoms Electrolysis H2O H+ + OH-

Electrolysis of Water Electrolysis is the production of a chemical reaction by electricity An electrolyte is a solution that conducts electricity by the movement of ions Sulphuric acid (H2SO4) is added to the water to help it to conduct electricity Breakdown water into it’s elements

Electrolysis of Water Hoffmann Voltammeter Acidified water Oxygen Hydrogen Cathode Anode Battery

Electrolysis of Water -Test for oxygen gas? H2 collects at the negative electrode (cathode) -Test for hydrogen gas? O2 collects at the positive electrode (anode) -Test for oxygen gas? Result: Twice as much hydrogen as oxygen is produced Conclusion: H2O molecule 2 hydrogen atoms for every 1 oxygen atom

H20 Molecule 1Oxygen atom 1 Hydrogen atom 1Hydrogen atom H H O Click on the page to form the water molecule 1 Hydrogen atom 1Hydrogen atom 1Oxygen atom

Assessment for lesson 1 What is the test for water? What is the freezing point of water? Describe an experiment to investigate dissolved solids in a water sample. Outline an experiment to determine the amount of hardness in a water sample.

Assessment for lesson 2 What is hard water? What causes water hardness? Name the two types of water hardness? How are they removed? What happens when hard water is passed through an ion exchange resin?

Assessment for lesson 3 What might you find dissolved in a sample of sea water? Outline an experiment to obtain a sample of pure water from sea water. Label diagram

Assessment for lesson 4 Why do we treat our drinking water? List the six steps in water treatment? Why is chlorine added to our the water? Where else have you seen chlorine added to water? Why is fluorine added to our drinking water? Where else have you seen fluorine added?

Assessment for lesson 5 What is electrolysis? Name the apparatus used to electrolyse water? What are the anode and the cathode? What are the results of the electrolysis experiment? What does the electrolysis experiment prove?