ACID RAIN

Rain water is naturally acidic because it contains dissolved carbon dioxide.The combustion of fossil fuels produces oxides of nitrogen and sulphur.These oxides dissolve in rain water and increase its acidity above natural levels.
Acid rain is rain that is artificially more acidic than normal.
The control of acidity is vital to living organisms, which have in-built systems for keeping the acidity of their tissues constant.
Acid rain also leaches metals from soil and rocks into streams and lakes.

WHAT ARE SUPERCRITICAL FLUIDS?

A modern method of making decaffeinated coffee depends on the properties of carbon dioxide above its critical temperature(31 degree celcius).This supercritical fluid (SCF) can dissolve caffeine from raw coffee beans , without dissolving most of the substances responsible for coffee's taste and flavour.After pumping away the solution of caffeine in SCF, carbon dioxide , the coffee beans are free of caffeine: any residual carbon dioxide disperses away.

And there you have it ... decaffeinated coffee

HOLIDAY HOMEWORK -FORM 4/ 2009

1
Diagram 1 shows the chemical symbols which represent four elements W, X, Y and Z.
Rajah 1 menunjukkan simbol yang mewakili empat unsur iaitu unsur W, X, Y dan Z.

12
W
6

7
X
3

14
Y
6

40
Z
18




Diagram 1
Rajah 1


(a)
State the number of electrons and neutrons in atom Z.
Nyatakan bilangan elektron dan neutron dalam atom Z.

Number of electrons: ……………. Number of neutrons: ………
Bilangan elektron : Bilangan neutron:
[2 marks]
[2 markah]


(b)
(i )
Define nucleon number.
Takrifkan nombor nukleon.

………………....………………………………………………………………...

..………………………………………………………………………………….
[1 mark]
[1 markah]



(ii)
State the nucleon number of atom Z.
Nyatakan nombor nukleon bagi atom Z.

........…………………………………………………………...............................
[1 mark]
[1 markah]



(c)
(i)
Write the electron arrangement of atom X.
Tuliskan susunan elektron bagi atom X.

…………………………………………………………………………………...
[1 mark]
[1 markah]



(ii)
Draw the electron arrangement of atom X to show the position of protons, neutrons and electrons in the atom.
Lukis susunan elektron bagi atom X untuk menunjukkan kedudukan proton, neutron dan elektron dalam atom.









[2 marks]
[2 markah]


(d)
(i)
Which two elements are isotopes?
Dua unsur yang manakah merupakan isotop?

…………………………………………………………………….......................
[1 mark]
[1 markah]



(ii)
Explain why isotopes of an element have the same chemical properties.
Terangkan mengapa isotop sesuatu unsur mempunyai sifat kimia yang sama.

…………….……………………………………..………………………………
[1 mark]
[1 markah]



(iii)
Give one usage of the isotope mentioned in (d) (i).
Beri satu kegunaan isotop yang dinyatakan dalam jawapan (d) (i).

…………………………………………………………………………………..
[1 mark]
[1 markah]



2(a)
What is the meaning of chemical formula?
Apakah maksud formula kimia?

...………….………………………………………………………………………………......... [1 mark]




b)
Table 2 shows the results of an experiment carried out by a student.Jadual 2 menunjukkan keputusan eksperimen yang dilakukan oleh pelajar.

Mass of combustion tube + porcelain dish
Jisim tiub pembakaran + mangkuk porselin
30.24g
Mass of combustion tube + porcelain dish + copper (II) oxide
Jisim tiub pembakaran + mangkuk porselin + kuprum(II) oksida
32.26g
Mass of combustion tube + porcelain dish + copper
Jisim tiub pembakaran + mangkuk porselin + kuprum
31.86g

Table 2
Jadual 2




(i)
Calculate the number of moles of copper in this reaction.[Relative atomic mass : Cu = 64]Kirakan bilangan mol kuprum dalam tindak balas ini. [Jisim atom relatif :i Cu= 64]







[1 mark]
[1 markah]




(ii)
Calculate the number of moles of oxygen in this reaction.[Relative atomic mass : O = 16]Kirakan bilangan mol kuprum dalam tindak balas ini.[Jisim atom relative: O= 16]





[1 mark]
[1 markah]



(iii)
Determine the empirical formula of copper (II) oxide.Tentukan formula empirik kuprum (II) oksida.

HOLIDAY HOMEWORK -LOWER 6 SCIENCE 2009

1. a) i Define relative atomic mass.
ii. The relative atomic mass of X is 30.97. How many
times is an atom of X heavier than a carbon-12 atom?
iii. Sulphur exists naturally as a mixture of four isotopes
with relative abundance given below.

Relative atomic mass
Relative abundance(%)
31.97
95.02
32.97
0.75
33.96
4.21
35.96
0.02
Calculate the relative atomic mass of sulphur.
(6m)
b) An element Y is a gas at ordinary conditions. The density of
Y is 1.11 gdm-3 at temperature 25°C and pressure 86.1 kPa.
i) Starting with the Ideal Gas Equation, calculate the relative molecular mass of Y and identify the gas. ( 3m)
c) A mixture of gas contains two isotopes of hydrogen:
Hydrogen-1 and Hydrogen-2
20 dm3 (at s.t.p) of the gas mixture has a mass of 1.80g.
Calculate the percentage of Hydrogen-1 in the mixture. (3m)

2. An organic compound, A , has the following composition by mass:
C:17.8% , H:1.5% , Cl: 52.6%, F:28.1%0
The mass spectrum of the compound shows a peak with the highest m/e
value at 138.

a) Calculate the empirical formula of A.
b) Determine the molecular formula of A. ( 4)

3. An element X has 2 isotopes, 36X and 38X .The mass spectrum of X shows two groups of lines as given in the table below:
Group
m/e value
Relative abundance
A
36
38
0.7
0.3
B
72
74
76
x
y
z







a)Identify the ions responsible for each of the lines.
b) Calculate the values of x, y and z. (10)


tigs2009L6Sc@suhaila

A+ CHEMISTRY TIPS

1.SET A GOAL
2.WORK TOWARDS YOUR GOAL
3.LISTEN ATTENTIVELY
4.UNDERSTAND CONCEPTS CORRECTLY
5.ASK WHEN NECESSARY
6.TAKE DOWN NOTES DILIGENTLY
7.ATTEMPT QUESTIONS FREQUENTLY
8.REVISE AND RECALL DILIGENTLY
9.MEMORISE EVERYTHING NECESSARY
10.DO CALCULATIONS METHODOLOGICALLY
11.REPAET AND RETEST WEEKLY
12.TRACK YOUR PROGRESS PERIODICALLY
13.HAVE FAITH AND BELIEVE IN YOURSELF

"PLAN YOUR WORK ... AND WORK YOUR PLAN "

THE GREAT TEACHER

THE GREAT TEACHER IS NOT THE ONE WHO SUPPLIES THE MOST FACTS,
BUT THE ONE WHOSE PRESENCE WE BECAME DIFFERENT PEOPLE !!

-RALPH WALDO EMERSON