Halo all students preparing for your O Level exams,
Do try out the following Chemistry Question from the Top 5 Sec Schools in Singapore during their Preliminary Examinations:
Question:
The number of atoms in 25g of Butane is:
A. 3 X 10^23
B. 3.6 x 10^24
C. 4.2 x 10^23
D. 4.2 x 10^24
Do try and send me your answers, probably by the email or leave a comment below the “COMMENT” section.
All the Best
Sean
Master Trainer =)
Err, how do you even do this question in the first place? =/
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sean Reply:
April 24th, 2009 at 4:27 pm
Have you covered Mole Calculations in school?
Regards,
Sean Chua=)
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MR(C4H10)= 4(12) +8 =58
no. of moles of C4H10=25/58
no. of molecules=(25/58)x(6×10^23)
no. of atoms=(25/58)(6×10^23)(14)=3.621×10^24
hence answer should be B.
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Well Done Lijun. This is a Cedar Girl O level Prelim MCQ and understand that couple of classes were tricked.
For Anonymous, hope you understand what Lijun has done to get the answer. The tricky part is to multiple by 14. Avogadro’s number is formally defined as the number of PARTICLES in 1 mole of substance. Do note that PARTICLES can refer to molecules, ions or atoms.
No. of molecules=(25/58)mole x(6×10^23)molecules/mole
No. of atoms=(25/58)(6×10^23)molecules x number of atoms in C4H10(14atoms)=3.621×10^24 atoms
Hope this helps. Let me know if you need more help in this.
Rgds,
Sean
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GOODEVENING SIR, PLEASE I HAVE BEEN ENCANTERING DIFFICULTIES WHEN SOLVING MOLE CONCEPT QUESTIONS, PLEASE, ADVICE ME ON WHAT TO DO. THANKS, SAMUEL FROM NIGERIA.
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sean Reply:
April 24th, 2009 at 4:23 pm
Hi Samuel,
Thanks for your comment.
For Mole Calculations, it requires you to be proficient with mathematical manipulations. You should have been taught the necessary mole calculations mathematics formulae required. All is required is to know how to apply them.
I have posted quite a number of questions (and suggested solutions) previously regarding Mole Calculations.
Go to the “SEARCH” field on the right hand side of this webpage and key in “Mole Calculations”. You will be directed to another page on the archive blogposts related to Mole Calculations.
Hope this information is useful to you.
Drop me a line or two. I would love to hear your success.
To Your Academic Success in Chemistry,
Sean Chua
Master Trainer & Author
WINNERS Education Group
“Experience Learning with A Difference”
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ravivenkatakrishna Reply:
March 2nd, 2011 at 3:52 pm
3*10 to the power of 23
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Goodmorning sir,am having difficulties about mole conceptions,am unable to understand a thing
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hi sir i m hving problems in mole concept pls give some tricks
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sean Reply:
April 28th, 2011 at 10:24 pm
Hi,
You can do a keyword search for “Mole Calculations” on the top right-hand corner of this website.
From there you can find more discussions on mole calculations.
Rgds,
Sean Chua
Reply
GMM of C4H10=4*12+1*10
=48+10
=58gm
58gm 0f C4H10=1 mole
hence, 25gm of C4H10= 25/58 moles
1 mole=6.023*10^23 molecules
hence, no.of atoms=(25/58*6.023*10^23)*14 atoms
=3.634*10^24 atoms to be exact.
and so according to the options present, the answer should be B.
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