### 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

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