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Calculating amount of molecules

Posted: Thu Jun 27, 2019 12:58 pm
by Blanca Cervantes
Can anybody explain how they went about solving the following problem?:

Calculate the amount of urea molecules, OC(NH2)2, in 2.3 x 10^5g of urea, which is used in facial creams and, on a bigger scale, as an agricultural fertilizer.

The correct answer is 3.8 x 10^3, but I keep getting a different number. I solved this problem by first dividing the total mass of the sample by the molar mass and then multiplying my result by Avogadro's constant.

My steps:
Finding molar mass:
m(O) + m(C) + m2(N) + m4(H) = 60.055

Dividing mass sample by molar mass:
(2.3 x 10^5)/ 60.05526= 3829.80

Multiplying the amount (in moles) by Avogadro's constant
N= 3829.80 x 6.022x10^23= 2.306 x 10^27

Re: Calculating amount of molecules

Posted: Fri Jun 28, 2019 10:47 am
by George_Zhu
Comparing with the correct answer and your answer, the goal of this question is to calculate amount of the substance in unit mol, instead of the number of the particle.

Re: Calculating amount of molecules

Posted: Fri Jun 28, 2019 2:06 pm
by Kevin To 1B
Blanca Cervantes wrote:Dividing mass sample by molar mass:
(2.3 x 10^5)/ 60.05526= 3829.80


That right there is 3.8 x10^3 moles, as indicated by your answer. Is there any chance the question asks for the amount in moles instead of molecules? (as a typo)

Re: Calculating amount of molecules

Posted: Sun Jun 30, 2019 7:29 pm
by Blanca Cervantes
There most likely was a typo in the textbook question