Chemistry of Water Starter: The answer is ‘Water’ What was the question? In the BACK of your book, write at least 3 questions (or as many as you can think of), to which the answer would be ‘Water’

Sir What do I do if I’m stuck?

Chemistry of Water PGCE Science Booster Session Graham Clarke

Chemistry of Water Traffic light Activity Not too Sure Do not Know OK

Physical Properties of Water How the hardness of Water Occurs Difference Between Temporary and Permanent Hard Water Acids and Alkalis Traffic Light Activity: RED – Don’t know AMBER - Unsure GREEN - OK

A Strange Molecule Ubiquitous No Taste No Smell No Form Transparent WATER

Water is Everywhere 80% Potato 75% Bacterium 74% Cow 65% Human 1.3 billion Km 3

Water is so common we tend to overlook what an extraordinary molecule it is

Phases of Water ICE WATER STEAM

If you compare water with similar molecules: It should be a gas at room temperature It should contract and become more dense when it freezes

Why? Hydrogen bonding Bonds between water molecules are very strong

Hydrogen bonds: Surface tension Water is a liquid at room temperature

HARD and SOFT WATER:  Many compounds dissolve in water without chemical change but may have a variety of consequences!  Some of these dissolved substances make the water hard. This means the water does not readily give a good lather  Most hardness is due to water containing dissolved calcium or magnesium compounds.

Hard water can be made soft By: removing the dissolved calcium and magnesium ions. –If due to hydrogencarbonates it is removed by boiling The addition of sodium carbonate (as 'washing soda' crystals), which dissolves and precipitates out the calcium or magnesium ions as their insoluble carbonates

Practical 1 Testing for Hardness of Water

ACIDS Acids and Alkalis ACIDS 2. acids have a pH less than 7, and turn universal indicator: red (if strong) or yellow (if weak) 2. acids have a pH less than 7, and turn universal indicator: red (if strong) or yellow (if weak) 1.acids are substances that form hydrogen ions, H+ (aq), when added to water 1.acids are substances that form hydrogen ions, H+ (aq), when added to water

ALKALIS Acids and Alkalis ALKALIS 2. alkalis have a pH more than 7, and turn universal indicator dark blue (if strong) or blue (if weak) 2. alkalis have a pH more than 7, and turn universal indicator dark blue (if strong) or blue (if weak) 1.alkalis are substances that form hydroxide ions, OH– (aq), when added to water 1.alkalis are substances that form hydroxide ions, OH– (aq), when added to water

The Arrhenius definition of an acid and a base: Acids - substances that when dissolved in water release H+ ions Bases - substances that when dissolved in water release OH- ions ACIDS and BASES

HCl is an Arrhenius acid: When HCl dissolves in water it actually transfers a proton to a water molecule: HCl(g) + H 2 O(l) H 3 O + (aq) + Cl - (aq)

The Brønstead-Lowry definition of an acid and a base: Acids - a substance that can transfer a proton to another substance Base - a substance that can accept a proton from another substance These definitions emphasize proton transfer, and can include solvents other than water ACIDS and BASES

HCl(g) + H 2 O(l) H 3 O + (aq) + Cl - (aq) In the reaction of HCl with H 2 O, HCl is a Brønstead-Lowry acid (donates a proton to H 2 O), and the H 2 O (in this particular reaction) is a Brønstead-Lowry base (accepts a proton from the HCl)

The pH Scale

Practical 2 Chemical Remedy Investigation

11 The three key words this lesson were… They link together because…

22 Next, I think we will be learning how to…

33 Pass! Ask the teacher a question!

44 I think it’s important to understand… so we can…

55 The key idea today was… The key idea today was… The reasons for this are… The reasons for this are…

66 I wonder if… is also the reason we…

77 The main idea today was that… and this happens because…

88 The most difficult thing to understand this lesson was... Because...

99 One thing we need to understand more about is… because…

Chemistry of Water PGCE Science Booster Session Graham Clarke