revision form 5-hari galas =chem presentation in the main hall

2. hydrophilichydrophobic
Hydrophilic:
Dissolve in
water
Hydrophobic:
Dissolve in
grease

3. c) State 2 advantages of soap over
detergents
d) How does soap cleanse grease?
-Biodegradable
- do not harm aquatic life
-Soap dissolves in water and lowers surface
tension of water making the clothes wet
-The hydrophibic part dissolve in grease,
the hydrophilic part dissolve in water
-Movement of water helps to loosen the
grease into small droplets

4. -The droplets do not coagulate due to the
repulsion between the negative charges
on their surface.
-Rinsing washes away these droplets and
leave the surface clean
7) State 2 advantages of detergents
-Effective in hard water and soft water
- effective in acidic water

5. 8) Why does bronze harder than copper?
The presence of tin atoms disturb the
orderly arrangement of copper atoms.
When force is given, the layers of atoms
do not slide easily

6. 9) Heating copper(II) carbonate
a)Write the chemical equation
b) State 2 observations
c) If copper(II) nitrate is heated, the chem.
equation
-limewater becomes milky
-black powder formed
23 COCuOCuCO +→
2223 42)(2 ONOCuONOCu ++→

7. 10) Heating of naphthalene
a)Melting point of naphthalene
b)What is the function of bath tub?
c)What precautions to be taken to obtain
a good graph?
Give uniform heating for naphthalene
80o
C
Naphthalene must be stirred continously
during heating

8. 11) To determine heat of combustion of
methanol
a)State 3 precaution to obtain a good
reading?
-water in copper can must be stirred
continously
-the spirit lamp must be closed
immediately with cap after heating to
avoid hot alcohol from evaporating
- Wooden block must be used to make sure
the wick touch the bottom of copper can

9. 12) To determine the empirical formula
of copper(II) oxide
a)Chemical equation
a)State 2 precautions
-Hydrogen gas must be allowed to pass
through combustion tube for a few minutes
before CuO is heated
-Flow of hydrogen gas must be continued
throughout heating
OHCuHCuO 22 +→+

10. To determine the empirical formula
magnesium oxide
Chemical equation
State 2 precautions
agnesium ribbon must be cleaned using
andpaper
e crucible lid must be open from time to
me to allow oxygen react with
agnesium
MgOOMg 22 2 →+

11. Electrolysis of copper(II) sulphate soltn
Half equation at cathode
Half equation at anode
Observation at cathode
own solid deposited
Observation at anode
ervescence occur
eOHOOH
CueCu
424
2
22
2
++→
→+
−
+

12. Simple voltaic cell
Half equation at –ve electrode
half equation at +ve electrode
Observation at –ve electrode
agnesium electrode becomes thinner
Observation at +ve electrode
ervescence occur
2
2
22
2
HeH
eMgMg
→+
+→
+
+

13. Experiment to show transfer of electron
a distance
Half equation at +ve electrode
half equation at -ve electrode
Observation at +ve electrode
own solution turns to colourless
observation at -ve electrode
our changes from colourless to brown
eII
BreBr
22
22
2
2
+→
→+
−
−

14. Preparation of soap in laboratory
Name of reaction: Saponification
What is the function of concentrated
alkali? To hydrolyse the oil
Observation:
hite precipitate that formed foam when
aken with water
Salt is added to the mixture during exp.
Why?
precipitated the soap produced

15. ) Energy level diagram for an exothermic
action
4 informations can be obtained:
1 mole of NaOH react with 1 mole HCl to
rmed 1 mole of NaCl and 1 mole of H2O
Energy level for reactant is higher than
nergy level for product
An exothermic reaction
Heat of reaction = -54kJmol-1

16. Relationship between:
Volume of gas against time
te of reaction decreases with time
oncentration of sodium thiosulphate
against time
hen the concentration of sodium
osulphate increases, the shorter the
me taken for reaction to occur

17. iii)Concentration of sodium thiosulphate
against 1/time
Concentration of sodium thiosulphate
is directly proportional to 1/time
iv) Temperature of solution against time
When temperature of solution increases,
the shorter time taken for reaction to
occur
v) Temperature of solution against 1/time
Temperature of solution increased
proportionally with 1/time