The wonderful solvent water

lovinggudgeonMechanics

Feb 22, 2014 (3 years and 3 months ago)

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5

T
h
e wonderful solvent


water

Mastering Science



© Oxford University Press 2010

-

1

-


Short notes for revision

1





Importance of water

1

We need water to survive and to carry out daily activities.




Making water safe to drink

1

Natural water

contains different types of

imp
urities
:

a

soluble impurities
;

b

insoluble
impurities
;

c

micro
-
organisms
.


2

T
wo common micro
-
organisms found in natural water
:




E
. coli

(x19 000)




A
moeba

(x160)


3

M
ethods of water purification
:

a
Sedimentation




Large and heavy solids settle at the
bottom

of the water. The
layer of impurities
settled
is called

sediment
.




5

The wonderful solvent


water


5
.
1

5
.
2



5

T
h
e wonderful solvent


water

Mastering Science



© Oxford University Press 2010

-

2

-


Short notes for revision

1














Adding
a
lum

can help remove the fine solid impurities suspending in water.



b
Filtration




Can
remove
solid impurities in water
.



Cannot remove micro
-
organisms and
soluble

impur
ities.



Filter columns

and
filter papers
are
filters

commonly used in the laboratory
.



The
liquid
that
passes through the filter is called

filtrate
.



The
solid
s

that

remain

in the filter is called
residue
.




















sediment





fine solids
suspending in
water




fine solids floating
on water


pond water



f
ine

sand

coarse sand

rock chips

small

stones

cotton

filtrate



Using f
ilt
er colu
mn

pond water



filter

paper


filter

funnel


filtrate





Using f
ilter paper



5

T
h
e wonderful solvent


water

Mastering Science



© Oxford University Press 2010

-

3

-


Short notes for revision

1


c
Distillation



C
an
remove all th
e
soluble
impurities
, insoluble impurities and micro
-
organisms

in

water
.






4

S
ummary of
the

impurities removed by different methods of water purification:

Method of
water
purification

Types of impurities removed


Insoluble impurities


Soluble

impurities

Micro
-
organisms

Large and heavy solids

Fine solids

Sedimentation









Filtration









Distillation










5

Other methods for killing micro
-
organisms in water:

a

Chlorination

b

Adding
ozone

c

Using
ultra
-
violet light

d

Boiling




pond

water


round
-
bottom flask


thermometer


condenser

water

in



W
a瑥t
楳⁢潩汥搠瑯

steam
. Impurities
are left behind in the flask.



S
瑥t洠
灡獳敳⁴桲潵g栠瑨h⁣潮摥湳n爬r
潯汳⁤潷渠o湤⁣潮o湳n猠瑯

汩煵楤q
睡瑥t
.



周T
汩煵楤扴a楮敤⁩猠ia汬搠
distillate

or

distilled water
.

water

out



C
hlorine water is corrosive



A

drinking fountain using ultra
-
violet
light to sterilize water



5

T
h
e wonderful solvent


water

Mastering Science



© Oxford University Press 2010

-

4

-


Short notes for revision

1



6

In Hong Kong, fresh water comes from the

Dong Jiang

and from

rainwater
.


7

In Hong K
ong,
t
he

water

treatment

process

involve
s

sedimentation
,
filtration
,
chlorination

and
fluoridation
.


8

The
treatment process

in water treatment works:





9

All the w
ater treatment works
in Hong Kong
are
run by the
Water Supplies Department
.




The water cycle


1

When

water

particles absorb enough heat energy, they move more quickly. They finally
escape from the water surface to become water vapour. This process is called
evaporation
.


2

When

the water vapour cools down
, the water particles move more slowly. They stick
together to form water droplets. This process is called
condensation
.

5
.
3

natural

water


screen to remove

large solids


alum

and

lime added


rapid

mix chamber


flocculation

tank:
sedimentation
takes place here


filtration

tank

chlorine

added to

kill micro
-
organisms

fluoride

add
ed
to help prevent
tooth decay

clean

water chamber

water

pumping

station

distribution

system

sediment

disposal



5

T
h
e wonderful solvent


water

Mastering Science



© Oxford University Press 2010

-

5

-


Short notes for revision

1


3

The main processes in the
water cycle
:




4

T h e

r
a t e o f e v a p o r a t i o n

o f w a t e r i s

h i g h e r

w h e n
:



a

t h e s p e e d o f a i r i s h i
g h e r
;


b

t h e t e m p e r a t u r e i s h i g h e r
;



c

t h e
s u r f a c e a r e a o f t h e o bje c t e xp o s e d t o a i r i s
l a r g e r
;


d

t h e
h u m i d i t y i s l o w e r
.



E v a p o r a t i o n




C o n d e n s a t i o n



T r a n s p o r t a t i o n



R a i n i n g

W a r m a i r c a r r i e s w a t e r
v a p o u r u p t o t h e s k y



T h e

s u n h e a t s u p t h e
s e a s, r i v e r s a n d l a n d.


W a t e r g a t h e r s i n r i v e r s
a n d r e t u r n s t o
the

sea


Some water becomes
underground

water


hot

water

hot

water

plastic

wrap


Е

T
he water cycle











closed
container



5

T
h
e wonderful solvent


water

Mastering Science



© Oxford University Press 2010

-

6

-


Short notes for revision

1



Water conservation and pollution

1

Fresh water is a precious resource. We must
conserve

water
.

2

W
ays
of

sav
ing

water at home:

a

Take a shower instead of a bath.

b

Wash vegetables in a basin of water. Do not rinse vegetables under a running tap.

c

Fix dripping taps immediately.

d

Turn off the tap while brushing

teeth.

e

Follow the 3

R
s

principle

of waste ma
nagement
,

i.e.

reduce, reuse and recycle.




3

Causes and effect
s

of
water pollution
:

Cause

Effect on human and environment

a

S
ewage

from homes

and

restaurants

contains
detergents



P
hosphates

in detergents promote
the

growth of algae and
may lead to
a
red tid
e
.

b

S
ewage from
farms
contains
fertilizers



P
hosphates in fertilizers promote the growth of
algae
.

c

S
ewage

from
homes

and
farms

contains
human
and animal waste



T
he waste may carry harmful micro
-
organisms. Eating
seafood contaminated with these micro
-
organis
ms can
cause
food poisoning
.

d

S
ewage

from factories

contains
toxic chemicals



T
he toxic chemicals may contaminate seafood and cause
food poisoning
.

e

S
olid waste



S
ea animals die when they eat

the waste or get trapped in it
.

f

O
il from spills



O
il floats on wat
er and blocks air from going into the
water
. F
ish and other sea anim
als die due to a lack of
oxygen
.



S
eabirds die of hunger as their feathers
are stuck by oil and
cannot fly
.

5
.
4



R
ecycling bins



5

T
h
e wonderful solvent


water

Mastering Science



© Oxford University Press 2010

-

7

-


Short notes for revision

1


4

The Hong Kong government controls water pollution by
:

a

treat
ing

the sewage in
se
wage treatment works

run

by
the
Drainage Services
Department
;

b

introduc
ing

the
Sewage
Services C
harging
S
cheme

under the
Polluter
P
ays Principle
;

c


treating waste water that contains harmful chemicals

in
the
chemical

waste treatment
plant
;

d

passing

laws

to co
ntrol discharge of sewage
.





Dissolving


1

When a
solute

dissolves

in a
solvent
, a
solution

is formed.




2

Water is a good solvent but it cannot dissolve everything.


3

When no more solute can dissolve in a solv
ent, a
saturated

solution
is formed.


4

Different
substances
have different
solubilit
ies

in a solvent.
.


5

The

r
ate of dissolving

of
a solute
is
higher

when
:

a

the temperature of the solvent is higher
;

b

the solute

pieces are smaller in size
;

c

the solution is sti
rre
d
.



dissolving


5
.5

wat er (sol vent )


sal t
sol ut i on



Е


Е


Е

salt (solute)



5

T
h
e wonderful solvent


water

Mastering Science



© Oxford University Press 2010

-

8

-


Short notes for revision

1



Growing crystals


1

Crystals
can be formed by cooling down a hot saturated solution
. The formation of crystals
in a solution is called
crystallization
.


2

Crystals have
regular shapes

and
smooth surfaces
.



Crystals of the
same kind may have

different sizes but their shapes are the same.




Crystals of different substances may have

different colours and shape
s.


3


Method of growing crystal

The crystal formed

Size

Shape



C
ooling down a hot
saturated solution
quickly







Smaller

Same



C
ooling down a hot
saturated

solution
slowly







Larger



Solvent
s

other than water


1

Oils are insoluble in water but they are soluble in other

solvents
like

alcohol, nail varnish
remover,

thinner and

dry
-
cleaning liquid.


2

We
must
take p
recautions when handling

solvents other than water
.


5
.
6

5
.
7


Е


Е


Е


Е


Е


a well
-
shaped

crystal as seed



hot saturated
solution


hot

saturated
copper sulphate

solution


cavity

sli
de

Alcohol



Flammable



Read the hazard warning labels
before using solvents