My lousy Chemistry

Cham lor~ cham lor~ I've just realized my Chemistry very lousy.

I'm in the library now, doing my Chemstry ILT 1.

ILT stands for 'Independant Learning Task'. They're multiple choice questions that you answer then submit your score. It accounts for a part of our results. We have to complete these before the deadlines.

Look at these questions!! *shock* :

Question 12
The average atomic mass of Re is 186.207 amu. It is calculated from the two naturally occurring isotopes 185Re and 187Re. If the isotopic abundance of 185Re is 37.4% and the isotopic mass of 185Re is 184.953 amu calculate the mass of 187Re.
A. 187.001 amu
B. 186.956 amu
C. 186.998 amu
D. 187.113 amu
E. none of the above

Question 13
An alkali metal (Group 1) chloride contains 70.7% metal by mass. The alkali metal is:
A. Na
B. Li
C. Rb
D. K
E. Cs

Question 18
A compound that contains only carbon, nitrogen and hydrogen is 26.1% C and 13.1% H by mass. What is the empirical formula for this compound?
A. C3H3N
B. CN2H6
C. C2NH3
D. CN2H8
E. CH5N

Question 20
If the process below is only 80% efficient, determine the mass of SiO2 required to produce 11 .00 g of P4.

A. 31.87 g
B. 1.396 g
C. 25.49 g
D. 1.955 g
E. 135.4 g

Question 22
A 12 kg sample containing a mixture of CaO and CaCO3 is heated and 1.8 kg of carbon dioxide is released. Determine the % by weight of the CaCO3 in the original mixture.
A. 36 %
B. 39 %
C. 27 %
D. 23 %
E. 44 %

Out of 22, I can only do 13. Foong Ing (MSN) help me do another 2.

CHAM liao la me! Help! It's due Wednesday (18/3/2009). I've only got two days left. Haih... Give up. I go home first liao. Tomorrow baru worry again. If anyone knows how to do, teach me!!