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BIG PICTURE

What is the most expensive natural commodity?

Lear

ning

Obj

ectiv

es Content• Identify how water becomes hard• Start to compare and contrast soft water and

permanent or temporary hard water• Start to evaluate the advantages and

disadvantages of soft and hard waterSkill• Observation and measuring skillsBenefit• Explain why you will need more shampoo when

you go to London!• How some hard water maybe good for your health

Beco

min

g ha

rd!

Water as part of the water cycle is slightly acidic (CO2 from atmosphere forming carbonic acid, H2CO3(aq) and naturally comes into contact with rocks ...

Compounds of the rock then dissolve into the water.

Beco

min

g ha

rd!

limestone

So what is in limestone?

So what is in dolomite?dolomiteCaCO3

MgCO3 and CaCO3

These metals ions (what are these?) are what causes the hardness in water.

Describe how hard water is formed and what is found in hard water (D)

Sulfates (SO4)in rocks as well as carbonates

Becoming hard!So what would the reaction be for limestone?

EXTENSIONSo what would the reaction be for dolomite?

What are the reactants? Don’t forget

state symbols!

H2CO3(aq) + CaCO3(s) → Ca(HCO3)2(aq)

carbonic acid + calcium carbonate → calcium hydrogencarbonate

Start with word equation

Forms - calcium hydrogencarbonate

Obs

erva

tion

skill

!• Work in fours, on your table – number

yourselves; 1, 2, 3 and 4• 1s – collect tubes (HP, SW, HT, BT) & rack• 2s – collect syringe/pipette and liquid soap• 3s – get a ruler or borrow one• 4s – copy out quick table of results

• Each add EXACTLY TWO DROPS (why exact?)• Replace the bung

Water Type HP SW HT BT

Foam height (cm3)

SHAKE IT OFF!• For 1 minute of Taylor – vigorously

shake your tubes!• 1s & 4s – Write an observed conclusion • 2s & 3s – measure the height of foam and fill

in table

• 1s/4s – soap / pipette back• 2s/3s – ruler

and tube/rack back

What are the different water types?

• HP – Hard permanent SW – Soft water• TP – Temporary hard BT – Boiled temporary

What is the difference between temporary and permanent?

• Temporary contains hydrogencarbonate ions (HCO3-), which when heated decompose into carbonate ions (CO3

2-), which then go and react with soluble Mg and Ca, forming ......

Removing Temporary Hardness

Explain how hardness can be removed from temporary and permanent hard water (A/B)

Why can't we use this method to remove hardness on a large scale?

Form insoluble metal carbonates (limescale), but removing metal ions!

Permanent hard water contain sulfates which do not decompose when heated, so metal ions remain

What are the implications of different water types?

Soap lather with soft water

Soap lather with hard waterI can explain some

disadvantages of hard water (C)

Hard water makes it difficult to lather soap for washing bodies , dishes and clothes. A lot more soap has to be used with hard water – costing more!

I can explain some advantages of hard water (C)

Water from the south west

Water from the south

east – tastier?

What is the difference between these 2 glasses of

water?

Limescale means the heating of water is not as efficient - costing more!

I can explain some disadvantages of hard water (C)

There is also evidence that heart disease is reduced

Promotes healthy teeth and bones

Explain some advantages of hard water (C)

Hard water leaves soap scum in baths /sinks/tiles

and screens.

It is formed when the soap reacts with the ions

in the hard water.

Explain some disadvantages of hard water (C)

sodium stearate + Ca2+ calcium stearate + Na+

soap + hardwater scum + soluble ions

Evaluate hard and soft water ......

Soft PermanentHard

Temporary Hard

STUCK???

Minerals involved?

Advantages of this water?

Made by?

REALLY STUCKOR CHECK IF YOU HAVE GOT ...

Limescale made by …..

Sulfates not carbonates …..

Exam Question Review?

Can you complete the question?

How would you make the best bubble/s?

So back to bubbles .....