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 -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 "