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### Calculating amount of molecules

Posted: Thu Jun 27, 2019 12:58 pm
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
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
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
There most likely was a typo in the textbook question